Expert Strategies: Skull Base Reconstruction—Global Perspectives, Insights, and Algorithms through a Mixed Methods Approach

ABSTRACT

Objective

There is limited consensus on endoscopic skull base surgery (ESBS) reconstruction principles. This study aims to generate comprehensive themes regarding ESBS reconstruction by pooling the experiences of ESBS experts, with comparison to a literature review of current published evidence.

Methods

Structured qualitative interviews of ESBS experts regarding postoperative management and reconstruction of various defect locations were conducted.

Results

A total of 68 experts comprising 40 academic teams across 13 countries with an average of 18 years of ESBS experience were included. We propose 10 stepwise algorithms for common skull base reconstruction scenarios based on these expert interviews. When available, the nasoseptal flap is used for all high_flow cerebrospinal leak defects. Multilayered reconstruction is favored at all anatomical subsites with increasing number of layers for increasing defect size and complexity. Heterogeneity exists in terms of inlay technique and materials, free grafting versus various pedicled flap options for low‐flow defects or in the absence of a nasal septum, nasal packing, tissue sealant, lumbar drain use, and postoperative management. Commonalities and discrepancies between experts were summarized.

Conclusion

Skull base reconstruction and post‐ESBS management is highly complex with a wide variety of practice patterns and expert strategies. Further research of higher quality evidence is warranted to identify optimal management patterns, though the current work aims to inform surgeons on these controversial areas by drawing from numerous experiences.

1. Introduction

Endoscopic skull base surgery (ESBS) has undergone significant evolution and expansion in recent years. As such, diseases that were previously only addressed with open surgical approaches can now be approached endoscopically in a less invasive manner. Given the comparable and generally favorable outcomes, decreased morbidity, and less invasive nature, ESBS as a technique, and the number of centers providing these procedures, is on the rise [1, 2, 3, 4, 5]. A unique requisite of many cases of intradural ESBS is the creation of skull base defects with continuity between the sinonasal and intracranial cavities, with subsequent cerebrospinal fluid (CSF) leak. Skull base reconstruction (SBR) following ESBS is critical to prevent consequences of persistent CSF leaks (e.g., meningitis, pneumocephalus) [6, 7]. Despite increasing adoption, there are limitations and sequelae from SBR. There are also still major discrepancies in technical and postoperative management protocols following ESBS and SBR. Examples where no consensus currently exists include choice of reconstructive materials and layers (e.g., autologous or synthetic grafts versus vascularized flaps); indications for use of lumbar drains (LD), tissue sealants, and nasal packing; and timing and duration of postoperative activity precautions and interventions [8].

Several societal membership survey‐based studies have aimed to address these gaps by reporting on the practice patterns of skull base surgeons, but there remain important unanswered questions and inconsistencies that require further investigation [9, 10, 11, 12, 13, 14]. This is hindered by the lack of objective and granular data, and the many nuances regarding SBR. Accordingly, an untapped resource for elucidating broad, unifying themes in areas of controversy is via qualitative research techniques [15]. Such methodology can elucidate practice patterns from the expertise of a representative group, which can provide crucial clarity in clinical situations for which there is otherwise little evidence.

The complexity of ESBS continues to require a high degree of experience, technical capability, and perioperative planning with multidisciplinary counterparts in a team‐based fashion. A relatively steep learning curve exists when performing team‐based ESBS, and with time, one's team becomes more proficient at managing progressively more complex scenarios. While practice patterns are initially largely based on individual surgeons’ training backgrounds, they are continuously adapted based on surgical evolution, research, and personal experience. Both the International Consensus Statement on Endoscopic Skull Base Surgery (ICSB) and the first evidence‐based review study regarding postoperative protocols following ESBS have highlighted the heterogenous, scarce, and low‐quality nature of the available data. Thus, there is an urgent need for higher quality studies based on the known research gaps [5, 8]. As such, the primary aim of this study is to consolidate the accrued experiences and techniques of ESBS experts utilizing a mixed methods qualitative interview‐based analysis in an effort to provide a comprehensive framework for SBR and postoperative management, as they relate to defects in various locations ranging from straightforward to the rare, challenging, and unresearched scenarios. The ultimate goals of this study are to highlight key surgical techniques in relation to published evidence (especially for early career surgeons), form the basis for the future development of ESBS protocols, and improve patient outcomes while minimizing risks, costs, and adverse events.

2. Methods

Given no risk (Part I—interviews) and its deidentified, voluntary participatory nature, this work met the exemption criteria by Institutional Review Boards at all investigators’ institutions.

2.1. Part I: Expert Interviews

A steering committee consisting of a multidisciplinary team of endoscopic skull base surgeons across multiple institutions with a common interest in SBR was formed. This group initially brainstormed key topics in SBR and created a list of questions (Figure S1) in interview format. The committee then generated a multidisciplinary, international, and multi‐institutional list of expert skull base surgeons and teams based on one or more of the following criteria: first/senior author peer‐reviewed publications on SBR and/or CSF leak repair; known high‐volume intracranial skull base and/or sinonasal malignancy practice; and/or frequently invited speaker or panelist on SBR and/or CSF leak topics at national and international conferences. These experts were also drawn from the membership of one or more academic societies (American Rhinologic Society [ARS], North American Skull Base Society [NASBS], American Head and Neck Society [AHNS], European Rhinologic Society [ERS]). Although many institutions have several ESBS experts meeting the inclusion criteria, the opinions and interview results of experts from a single institution were only weighted once (not individually) in order to foster balanced representation, avoid redundancy, and minimize bias of the overall results. Specifically, an identified team with multiple surgeons was invited to interview together as a group to report their shared strategies that were collated into a single set of answers. If practice patterns for experts at the same institution varied for any question, all utilized management styles or reconstructive techniques were recorded and reported as “option A or B is used by this expert group.” This is partially why the sum of percentages for certain answers are larger than 100%. Each expert team was asked to answer these questions by the members of the steering committee through face‐to‐face interviews, video conferencing software, and/or in written form. If all team members were unable to participate during the interview, the team representative provided answers on behalf of the team and the compiled answers were subsequently shared with the team members not present at the interview for additional edits, review, and approval.

2.2. Part II: Definitions

All defects were assumed to have an active CSF leak (i.e., there were no questions on strategies for reconstruction in the absence of a CSF leak). For each defect location, the experts were asked to consider the largest possible size (i.e., anatomical limits) when providing their opinion on reconstruction technique. Experts were also asked to provide reconstructive algorithms when a nasoseptal flap (NSF) was not available for use. Inlay (underlay) materials were those placed deep to the dura (subdural) and/or bone of the skull base (epidural; between dura and bone), and experts were asked to specify the anatomic space within which each inlay layer was placed. Onlay (overlay) materials refer to those placed over the bone of the skull base, or dura when there are no bony skull base edges available for inlay placement. Of note, inlay and onlay usage are reported separately to promote clear granularity of data and in order for different layers of reconstruction to be analyzed independently.

Experts were also asked to specify the locations from which they would derive free grafts and vascularized flaps. Autologous materials referred to those derived from the patient (e.g., fat, fascia lata [FL]), while synthetic (nonautologous) materials referred to xenografts that do not require harvest via a donor site (e.g., commercially available products). Synthetic materials were further divided into collagen matrix (e.g., Duragen [Integra Lifesciences, Princeton, NJ], Duramatrix [Stryker, Portage, MI]), extracellular matrix (ECM)‐based scaffolds (e.g., Biodesign [Cook Biotech, West Lafeyette, IN], Alloderm [AbbVie Inc., Chicago, IL]), and hemostatic materials (e.g., gelatin). The term free nonmucosal graft referred to nonvascularized tissue other than mucosa used as onlays and could be either autologous (e.g., FL) or synthetic (e.g., Biodesign graft). The weeping CSF leak following sellar surgery referred to a subtle defect but obvious egress of CSF from the edges of the sella or exposed diaphragma, akin to Esposito grade 1 leaks [16]. For sellar defects, a subdural graft was defined as being placed deep to the sellar dura (anterior wall and floor), but not the diaphragma sella (which is typically largely intact in this scenario). Refractory leaks were defined as postoperative CSF leaks that persisted despite two or more repair attempts. Answers to interviews were then recorded and analyzed by the steering committee, with conflicts in interpretation resolved by the senior author (E. C. K.).

2.3. Part III: Description of Mixed Methods Approach and Data Analysis

We utilized a mixed methods technique involving qualitative and quantitative analysis of the collected data. For the qualitative portion, a grounded theory methodology was employed to generate common expert viewpoints for each topic; these themes were iteratively reviewed and presented back to experts for approval in order to create central codes capturing the crux of multiple and common expert recommendations [15]. Interviews were continued until data saturation and then 10 additional interviews were conducted to ensure complete content capture. Furthermore, care was taken to capture the complete breadth and depth of topics as experts from different training backgrounds within SBR across different years of expertise were interviewed. Experts’ answers were reported back to them after data aggregation, and any corrections were incorporated for consistency and accuracy of data analysis.

During data analysis, we encountered expected heterogeneity among responses. Nevertheless, themes emerged within the collected data, which were then compiled into technical algorithms for step‐by‐step reconstruction of specific defects. These data were further analyzed using quantitative methods, with descriptive data reported for specific reconstructive materials, scenarios, and postoperative precautions.

3. Results

3.1. Profiles of Experts and Definitions of High‐Flow Leak

The interview consortium consisted of 40 expert groups with 68 individual experts representing 13 countries. On average, experts had 18 years of experience with SBR (range 5–40). Additionally, their definitions of high‐flow leak varied; the majority of experts (80%) mentioned defect communication with a subarachnoid cistern or ventricle, roughly half (47.5%) required intraoperative visualization of a “gush” of CSF or a “large” dural defect without specific size criteria, 17.5% had specific size criteria of 1–1.5 cm² or greater dural defect, and 10% considered factors such as obesity and elevated intracranial pressure (ICP) of any cause.

3.2. SBR Techniques and Algorithms

The following data are a summary of reconstructive techniques and types of graft materials used for skull base defects from the perspective of interviewed experts. The end products are proposed algorithms for reconstructing various ventral skull base defects derived from the most common expert practices.

3.2.1. Algorithm 1: Sellar Defect With Weeping Leak

Figure 1 depicts the interviewed expert algorithm for closure of a sellar defect with a weeping leak. The majority of experts utilized one (60%) inlay and one (87.5%) onlay layer, although roughly a quarter of experts used two or more inlay layers (27.5%).

FIGURE 1.

Expert reconstruction algorithm for a sellar defect with a “weeping” leak. ECM, extracellular matrix; FMG, free mucosal graft; INF, intranasal flap (excluding nasoseptal flap); NSF, nasoseptal flap. Italicized rows indicate most common response among experts for specific inlay/onlay.

The most frequently used inlay subdural layer is subdural collagen matrix, followed by fat. An epidural inlay was less frequently utilized, but when used, the most frequent materials were collagen matrix and FL. Additionally, 12.5% utilized rigid reconstruction. The most frequently used onlay reconstruction was the free mucosal graft (FMG) for both intact nasal septum (57.5%) and non‐intact septum (85%). The NSF was the preferred reconstructive method for 35% of experts when the nasal septum is intact, and other intranasal flaps were utilized by 10% of experts when the NSF was not available.

3.2.2. Algorithm 2: Sellar Defect With Visible Hole in Diaphragma

Figure 2 summarizes the reconstructive practices of experts when facing sellar defects with a visible hole in the diaphragma with arachnoid violation. Sixty percent of experts recommend at least two inlay layers although 40% used only one. Fat was the most common inlay material followed by hemostatic materials and collagen matrix, usually in the subdural space. Of note, 17.5% of experts consider a rigid inlay reconstruction. In terms of onlay materials, 97.5% of experts use one layer with the majority favoring a vascularized reconstruction. As a single layer, onlay reconstruction involves a NSF if the septum is present or a FMG or non‐NSF intranasal flap (i.e., lateral nasal wall flap [LNWF]) if the septum is absent.

FIGURE 2.

Expert reconstruction algorithm for a sellar defect with a visible hole in the diaphragm. ECM, extracellular matrix; FMG, free mucosal graft; INF, intranasal flap (excluding nasoseptal flap); NSF, nasoseptal flap. Italicized rows indicate most common response among experts for specific inlay/onlay.

3.2.3. Algorithm 3: Suprasellar Defect

Principles for suprasellar reconstruction are summarized in Figure 3. The majority of experts (62.5%) use two or more inlay layers while 35% use a single inlay layer. For onlays, 75% of experts use a single layer and 25% use two or more layers. Overall, the most common method of suprasellar (SS) reconstruction was two inlay layers consisting of subdural fat and/or FL and epidural FL with a single onlay layer. If the septum is intact, all experts utilize a NSF. However, onlay options are heterogeneous when the septum is not available, and many experts consider alternative vascularized options, with LNWF or extranasal pedicled flaps being the most frequently utilized (e.g., pericranium or temporoparietal fascia flap [TPFF]).

FIGURE 3.

Expert reconstruction algorithm for suprasellar (transtuberculum/transplanum) defects. ECM, extracellular matrix; ENF, extranasal flap; FL, fascia lata; FMG, free mucosal graft; INF, intranasal flap (excluding nasoseptal flap); NSF, nasoseptal flap. Italicized rows indicate most common response among experts for specific inlay/onlay.

3.2.4. Algorithm 4: Anterior Cranial Fossa or Transcribriform Defect

Figure 4 depicts varied practices of interviewed experts for reconstruction of large anterior cranial fossa (ACF) defects. Most experts (65%) prefer two or more inlay layers with 35% preferring a single inlay. With respect to the onlay, 67.5% prefer a single layer while 30% use two or more layers. Generally, inlay reconstruction of ACF defects involves two layers consisting of subdural collagen matrix, FL, and/or fat along with epidural FL. Onlay reconstruction is most commonly one layer and a NSF is ubiquitously the first choice when available. However, when the septum is unavailable, the most frequently harvested tissue is a pericranial flap, although the LNWF, free nonmucosal graft, and FMG are used by some teams.

FIGURE 4.

Expert reconstruction algorithm for anterior cranial fossa (transcribriform/transethmoid) defects. ACF, anterior cranial fossa; ECM, extracellular matrix; FL, fascia lata; INF, intranasal flap (excluding nasoseptal flap); NSF, nasoseptal flap. Italicized rows indicate most common response among experts for specific inlay/onlay.

3.2.5. Algorithm 5: Posterior Cranial Fossa or Transclival Defect

Posterior cranial fossa (PCF) defect repair was highly heterogeneous among experts, especially for inlay reconstruction (Figure 5). Experts most often used at least two inlay layers (70%) and onlay layers (55%). For inlay reconstruction, subdural fat and epidural FL are most common, with many experts reporting use of the “epidural tuck” technique (sub/epidural placement of the central part of a watertight layer, such as FL or acellular dermal matrix, with the peripheral regions constituting an onlay over bone and dura, and placement of a fat graft over the central area as an onlay), much akin to a “gasket seal.” However, many other inlay materials are considered, including collagen matrix (15%). The most frequent onlay reconstruction was NSF (95%). If the NSF was not available, other intranasal flaps (LNWF, 52.5%), extranasal flaps (TPFF, 40%), and free FL were frequently utilized. Of note, two (5%) experts would consider upfront free tissue transfer with microvascular anastomosis when the septum is unavailable.

FIGURE 5.

Expert reconstruction algorithm for posterior cranial fossa (transclival and/or craniocervical junction) defects. ECM, extracellular matrix; ENF, extranasal flap; FL, fascia lata; INF, intranasal flap (excluding nasoseptal flap); NSF, nasoseptal flap; PCF, posterior cranial fossa. Italicized rows indicate most common response among experts for specific inlay/onlay.

3.2.6. Algorithm 6: Traumatic Cribriform/Ethmoid Defect Failing Conservative Management

For traumatic cribriform/ethmoid defects that undergo immediate repair or have failed conservative management (management varied), experts preferred no inlay (47%) or one inlay (47%) layer, and one onlay layer (91.2%). A single FMG onlay layer was the most frequent approach (82.4%). Almost half the experts do not use any inlay graft, but when performed, a single subdural plug of collagen matrix or fat is preferred (Figure 6).

FIGURE 6.

Expert reconstruction algorithm for traumatic ethmoid defects. ECM, extracellular matrix; FMG, free mucosal graft; NSF, nasoseptal flap. Italicized rows indicate most common response among experts for specific inlay/onlay.

3.2.7. Algorithm 7: Iatrogenic Cribriform/Ethmoid Defect

For iatrogenic cribriform/ethmoid leak repair, the majority of experts preferred a single inlay (55.9%) while roughly a third preferred no inlay. Almost all experts (88.2%) utilize a single onlay layer with FMG (91.2%), followed by NSF as the next most preferred option (35.3%). If performed, a single inlay most often involves a synthetic material placed in the subdural or epidural space (Figure 7).

FIGURE 7.

Expert reconstruction algorithm for iatrogenic ethmoid defects. ECM, extracellular matrix; FMG, free mucosal graft; NSF, nasoseptal flap. Italicized rows indicate most common response among experts for specific inlay/onlay.

3.2.8. Algorithm 8: Frontal Sinus Posterior Table Defect

For frontal sinus medial posterior table defects, experts all preferred a purely endoscopic approach with either Draf 2b, Draf 2c, or Draf 3 procedures. For a lateral posterior table defect, the majority of experts prefer a combination of endoscopic and open techniques; 75% of experts utilize an endoscopic approach (Draf 2b, Draf 2c, Draf 3, and/or periorbital suspension [17]), and in terms of open approaches, transorbital or direct brow (32.5%), trephination (27.5%), and osteoplastic flap (22.5%) approaches were most frequently utilized. Most experts favor a single inlay (70.6%) with subdural placement of collagen matrix, ECM‐based scaffolds, fat, or FL. Almost all experts prefer one onlay layer (97.1%) with a FMG or NSF (Figure 8).

FIGURE 8.

Expert reconstruction algorithm for frontal sinus posterior table defects. ECM, extracellular matrix; FMG, free mucosal graft; NSF, nasoseptal flap; PT FS, posterior table of frontal sinus. Italicized rows indicate most common response among experts for specific inlay/onlay.

3.2.9. Algorithm 9: Spontaneous Ethmoid CSF Leak/Meningoencephalocele

Experts prefer an endoscopic approach with either no inlay (41.2%) or a single inlay layer (58.8%) with one onlay layer (94.1%) for repair of spontaneous ethmoid CSF leaks or meningoencephaloceles. When performed, the inlay is usually subdural and consists of heterogeneous synthetic or autologous materials. As seen in Figure 9, a FMG and NSF were frequently utilized onlay materials (64 and 50%, respectively).

FIGURE 9.

Expert reconstruction algorithm for spontaneous ethmoid leaks and encephaloceles. ECM, extracellular matrix; FMG, free mucosal graft; NSF, nasoseptal flap. Italicized rows indicate most common response among experts for specific inlay/onlay.

3.2.10. Algorithm 10: Spontaneous Sphenoid CSF Leak/Meningoencephalocele

As summarized in Figure 10, for spontaneous sphenoid lateral recess (SSLR) CSF leaks or meningoencephaloceles, the majority of experts favor placing at least one inlay graft (79.4%) and almost all experts prefer one onlay layer (97.1%). The choice of inlay materials varies, and notably, 23.5% of experts also prefer rigid construction as inlay reconstruction. Onlay repair materials included a NSF (both contralateral and ipsilateral were mentioned) or FMG.

FIGURE 10.

Expert reconstruction algorithm for spontaneous sphenoid sinus lateral recess leaks and encephaloceles. ECM, extracellular matrix; FMG, free mucosal graft; NSF, nasoseptal flap. Italicized rows indicate most common response among experts for specific inlay/onlay.

3.3. Other Techniques

Of note, there were several unique techniques that have been reported by some of the experts for various defects, including:

• Elevation of sphenoid mucosal flaps and replacement over skull base defect

• Endoscopic clipping of a diaphragma sellar arachnoid defect

• Endoscopic dural suturing, either to existing edges or to interposition inlay graft materials

• Calcium hydroxyapatite to fill a bony sellar, SS, and/or clival defect

• Suturing of the sphenoid face mucosa over a PCF defect

3.4. Dural Sealants

Table 1 summarizes dural sealant usage amongst experts. Of 38 expert groups who commented, 50% always use a dural sealant, 24% endorsed usage in specific situations, such as when there is “large defect” or NSF placement, and 24% never use dural sealants. The most common dural sealant was fibrin glue (35%) followed by Duraseal (Integra LifeSciences, Princeton, NJ; 27.5%) and Adherus (Stryker, Kalamazoo, MI; 20%). Of the 13 experts who commented on the location of dural sealant placement, the majority (n = 11) placed the sealant over the onlay with two using fibrin glue over the inlay but underneath the onlay. No experts reported placing Duraseal or Adherus over the inlay and deep to the onlay.

TABLE 1.

Dural sealant use and indications among experts.

Characteristics	# Experts	% Experts
Indications
Always	19	50.0%
Intraoperative CSF leak, large defect, NSF usage	9	23.7%
Never	9	23.7%
Tissue sealant types
Fibrin glue	14	35.0%
Duraseal	11	27.5%
Adherus	8	20.0%
Layer of use
Over onlay	11	84.6%
Over inlay—fibrin glue only	2	15.4%

3.5. Nasal Packing

Table 2 reports the practice patterns for nonabsorbable and absorbable nasal packing by experts following SBR. Fifteen (37.5%) always use nonabsorbable packing, seven (17.5%) never use it, four (10%) use it in “rare unique situations,” and four (10%) use it for high‐flow leaks (any definition). Two experts recommended it specifically for SS defects, three for PCF defects, and two for “large defects” of locations not otherwise specified. Other answers included nasopharyngectomy defects and large ACF defects especially when extending anteriorly toward the posterior table. In terms of preferred packing type, 57.5% of experts use Merocel (hydroxylated polyvinyl acetate; Medtronic, Minneapolis, MN) sponges, 22.5% use Xeroform (petrolatum and bismuth tribromophenate; various companies) or other types of strip gauze, and 12.5% use a foley balloon. Epistaxis balloons and nasal trumpets were mentioned rarely. Roughly a third (34.4%) of interviewees remove nonabsorbable packing within 48–72 h while another third (34.4%) remove nonabsorbable packing in 3–7 days. Only 12.5% of experts leave nonabsorbable packing in place for up to 14 days, with no correlation to the type of nonabsorbable packing.

TABLE 2.

Type of nasal packing, dressings, and bolsters used by interviewed experts after reconstruction of skull base defects by interviewed experts.

Characteristics	# Experts	% Experts
Nasal packing
No nasal packing	7	17.5%
Dissolvable
Oxidized cellulose	10	25.0%
Gelatin sponge	11	25.0%
Hemostatic slurry (Surgiflo, Floseal)	2	5.0%
Nasopore or Hemopore	18	45.0%
Posisep	0	0
Spongostan	1	2.5%
Nondissolvable
Gloved Merocel	23	57.5%
Vaseline or Xeroform strip gauze	9	22.5%
Foley balloon	1	2.5%
Duration
2–3 days	11	34.4%
3–7 days	11	34.4%
7–14 days	6	18.8%
>14 days	4	12.5%

Absorbable packing was always utilized by the majority of experts (60%), while 20% never use it. Seven (17.5%) expert groups use it in specific scenarios, such as with high‐flow leaks, sellar/tuberculum defects, or when a FMG or pedicled intranasal flap is used. Nasopore (Stryker) was the most common type of dissolvable packing used (60%) followed by gelatin sponge (Gelfoam; 27.5%) and oxidized cellulose (Surgicel; 25.0%). However, it is important to note that during interviews, several experts did not specify which type of dissolvable packing is used.

3.6. Lumbar Drain Utilization

As seen in Table 3, 92.5% of experts reported frequently using an LD in specific situations related to SBR. Common indications for LD included high‐flow CSF leak (37.5%), PCF defects (35%), risk factors for postoperative CSF leak (25%) such as prior radiation, technically challenging reconstruction as deemed by the surgeon(s), obesity/idiopathic intracranial hypertension (IIH), or recurrent postoperative CSF leak (22.5%). A fifth of experts highlighted elevated ICP as an indication for LD use. Only one expert stated that they always use an LD, whereas 7.5% never use an LD. The majority of experts drain CSF at a rate of 5–10 mL per hour and remove the drain after 48–72 h.

TABLE 3.

Indications and usage of lumbar drains after reconstruction of skull base defects.

Characteristics	# Experts	% Experts
Indication
Posterior cranial fossa defect	14	35%
High‐flow CSF leak	13	32.5%
Post‐op CSF leak risk factors	10	25%
Recurrent CSF leak	9	22.5%
High ICP concern	8	20%
Suprasellar defect	5	12.5%
Never use drain	3	7.5%
Lumbar drain duration
No lumbar drain	3	7.5%
24–48 h	2	6.9%
48–72 h	18	62.1%
>72 h	9	31.0%
Lumbar drain rate
Clamped (open as needed)	0	0
<5 mL/h	3	11.5%
5–10 mL/h	19	73.1%
10 mL/h	4	15.4%

3.7. Impact of Chemotherapy and Radiotherapy on Reconstruction Technique

SBR techniques among experts varied in the setting of previous chemotherapy, previous skull base radiation, and anticipated need for adjuvant radiation (Table 4). For patients with history or current use of chemotherapy, most experts (77.5%) did not change their reconstructive technique, while the rest favored using vascularized flaps over free grafts. If patients had prior skull base radiation, 80% of experts favored vascularized flap or autologous grafts, and 10% specifically mentioned using an LD. If adjuvant radiation therapy is planned, 35% of experts do not change their practice while 62.5% would be more inclined to use vascularized flaps or autologous grafts.

TABLE 4.

Effect of neoadjuvant and adjuvant therapies on expert reconstruction technique.

Response	Previous RT	Future RT	Chemotherapy
No change in algorithm	6	14	31
Favor flap	32	22	9
Favor LD	4	1	0
Favor autologous tissues	1	3	0

3.8. Diagnosis and Management of Early Postoperative CSF leak

If a postoperative CSF leak is suspected, workup among experts often includes computed tomography (CT) scan to detect pneumocephalus (42.5%), provocative tilt test to assess for clear rhinorrhea (42.5%), assessing for concerning symptoms (25%), beta‐2‐transferrin/beta trace protein testing (22.5%), bedside endoscopy (20%), urgent endoscopy with exploration in the operating room (22.5%), and injection of intrathecal fluorescein (10%). Interventions for early postoperative CSF leak included urgent exploration and revision (77.5%) as well as LD placement and bedrest (32.5%). Most experts did not comment on the timing of intervention, although nine (22.5%) did mention intervening either immediately or on the same day. A full summary of postoperative CSF leak evaluation and management among experts is presented in Figure 11.

FIGURE 11.

Expert algorithm for workup of suspected early postoperative CSF leak, with frequencies of expert responses.

3.9. Reconstructive Options and Management of Refractory CSF leaks and Non‐NSF Reconstructive Techniques

Experts had various strategies for the management of refractory leaks, as well as varying indications for TPFF, pericranial flaps, and free flaps and permanent CSF diversion (i.e., shunting) were elicited.

Common indications for a TPFF include when the septum is not available or failure/necrosis of intranasal pedicled flaps, especially for PCF defects, as well as PCF defects with concurrent skull base osteoradionecrosis (ORN). Less common TPFF indications were following a failed pericranial flap, SS defects with no available septum or failure/necrosis of intranasal pedicled flap, previous irradiation, and far lateral ACF or SS defects.

The most common indication for a pericranial flap was when the septum is not available or failure/necrosis of pedicled intranasal flaps especially for ACF defects. Less common indications for pericranial flaps were frontal sinus posterior table and SS defects with no septal availability or failure/necrosis of intranasal pedicled flaps, as well as previous irradiation.

Free flaps were considered when intranasal and extranasal pedicled flaps (TPFF and pericranial flap) had failed or were not available (especially for PCF with or without prior irradiation), when there are severe radiation changes to the skull base, and when the defect is exceptionally large, eccentrically shaped, and complex (e.g., concurrent orbital exenteration). Less common indications for a free flap included irradiated ACF defects and leaks refractory to LD placement.

Finally, shunting was rarely considered overall, but was discussed when persistently elevated ICP or IIH is suspected, after two seemingly adequate repair attempts had failed (regardless of ICP), and if a multiply refractory leak resolved or decreased after LD placement.

3.10. Postoperative Precautions and Management after SBR

Postoperative care protocols after SBR are summarized in Table 5. The majority of the expert teams preferred either no or <24 h of bedrest (60%). 25% of expert teams preferred bedrest between 24 and 72 h, while 5% of expert teams preferred >72 h bedrest. The majority of US experts preferred immediate mobilization or <24 h of bedrest; whereas non‐US experts preferred longer duration of bedrest. Some experts also made decisions on timing of bedrest based on LD placement or CSF leak flow rate.

TABLE 5.

Postoperative precautions and protocols among experts.

Precaution/intervention	Duration	# Experts	% Experts
Bedrest	None	10	25.0%
	<24 h	14	35.0%
	24–48 h	3	7.5%
	48–72 h	7	17.5%
	>72 h	2	5.0%
	“Depends”	4	10.0%
Nasal precautions and/or activity restrictions	<2 weeks	5	12.5%
	2–4 weeks	5	12.5%
	>4 weeks	30	75.0%
Straw use	OK	37	92.5%
	Restrict	3	7.5%
Timing to restart CPAP	Immediately*	3	7.5%
	<2 weeks	5	12.5%
	2–4 weeks	21	52.5%
	>4 weeks	6	15.0%
	“Depends”	5	12.5%
Timing to resume air travel	None	2	5.0%
	<2 weeks	18	45.0%
	2–4 weeks	15	37.5%
	>4 weeks	5	12.5%
Peri‐ and postoperative antibiotic use	Perioperative only	7	20.6%
	Postoperative only	8	23.5%
	Both	19	55.9%
Timing of debridement	<2 weeks	16	43.2%
	2–4 weeks	21	56.8%
Timing of saline irrigations	<2 weeks	19	54.3%
	2–4 weeks	10	28.6%
	4+ weeks	2	5.7%
	“Depends”	4	11.4%

^*Depending on the severity of OSA and/or no extended approaches were performed.

All expert teams agreed on enforcing nasal precautions after SBR. These restrictions included those intended to prevent rapid ICP shifts (i.e., limiting Valsalva through limiting straining, heavy lifting, strenuous activities, and nose blowing; sneezing and coughing with mouth open; head elevation, and use of stool softeners). The majority of expert teams (92.5%) placed no restrictions on use of straws by patients postoperatively. Assuming the largest defect size, most expert teams (75%) preferred >4 weeks of activity restrictions (generally up to 6 weeks), whereas 12.5% of expert teams favored <2 weeks or 2–4 weeks of postoperative activity restrictions each, respectively.

Regarding management of patients with obstructive sleep apnea (OSA) following SBR, experts were asked regarding timing of continuous positive airway pressure (CPAP) resumption. Most expert teams prefer restarting CPAP anywhere between 2 and 4 weeks (52.5%), while 12.5% of expert teams restarted CPAP within 2 weeks after surgery, and 15% of expert teams restarted CPAP after 4 weeks. A few expert teams started CPAP immediately after reconstruction depending on the severity of OSA and/or no extended approaches were performed.

Five percent of experts placed no timing restrictions for postoperative air travel, 45% of expert teams reported allowing air travel within 2 weeks after hospital discharge, 37.5% expert teams permitted air travel between 2 and 4 weeks after surgery, and only 12.5% of experts limited air travel until >4 weeks after surgery.

Most expert teams preferred to prescribe antibiotics perioperatively or postoperatively after ESBS (89%). Out of these expert teams, 55.9% used both perioperative and postoperative antibiotics, 23.5% of expert teams utilized postoperative antibiotics only, and 20.6% of expert teams used perioperative antibiotics only. There was significant heterogeneity in duration of antibiotics, though a common theme was that patients remained on antibiotics until nonabsorbable packing was removed or until first postoperative debridement. Most experts preferred either intravenous first‐ or second‐generation cephalosporins, vancomycin, or ampicillin–sulbactam or oral amoxicillin–clavulanate or cephalexin.

The majority of expert teams performed the first debridement 2‐4 weeks after surgery (56.8%), while the remainder preferred debridement within 2 weeks of surgery. Most experts agreed to wait until the second or third postoperative visit for comprehensive debridement around the vicinity of the skull base.

Most expert teams do not initiate saline sprays or irrigation in the immediate postoperative period to prevent masking a CSF leak. Most of the experts started saline sprays after discharge and saline irrigations after the first debridement or splint/packing removal. The timing of starting saline irrigations therefore correlated with timing of debridements, with the majority of experts starting the saline irrigations within 2 weeks after surgery (54%).

4. Discussion

This international multi‐institutional, multidisciplinary study aims to understand practice patterns and major themes in SBR and post‐ESBS care as well as highlight areas of controversy and debate within ESBS. Due to the lack of high‐level evidence on SBR and postoperative management, we utilized a qualitative research methodology. Our steering committee interviewed experts in a structured yet open‐ended manner to elucidate aspects of SBR they believe to be particularly important. The expert strategies described here can provide a reference point for intraoperative and postoperative decision making and raise important points that may direct future research [5].

4.1. Overarching Trends in Reconstruction

The main commonalities and points of divergence between expert teams for various SBR techniques and perioperative care are highlighted in Table 6. Assuming a multilayer repair process, inlay materials are usually placed in the subdural and/or epidural spaces, while onlay materials are typically grafts and flaps placed over the extracranial bony surface. The present expert interviews afford clarity on specific layers for inlay reconstruction as summarized in the algorithms (Figures 1, 2, 3, 4, 5, 6, 7, 8, 9, 10). Figure 12 further distills the information from these algorithms to present anatomic and surgical schematics for specific inlay and onlay placement strategies.

TABLE 6.

Summary of common practices and areas of divergence between experts for skull base reconstruction.

Topic	Common Themes	Discrepancies
“Weeping” sellar defects	At least one subdural inlay and one onlay layer is preferred FMG is the preferred onlay material when the septum is unavailable	Choice of inlay material is highly varied When a NSF is available, 57% prefer FMGs and 35% NSFs A few experts do not use an onlay
Sellar defect with hole in diaphragma	Multilayered reconstruction is usually performed with at least one inlay and one onlay layer Collagen matrix and fat are the most commonly used synthetic and autologous inlay materials A vascularized flap is preferred; a NSF is used when available	Inlay: 40% use one layer and 60% use two+ layers When the septum is unavailable, experts use either FMG or a nonseptal intranasal flap 17% prefer a rigid reconstruction A small minority of experts consider sphenoid rostral mucosal flaps or calcium hydroxyapatite
Suprasellar (transtuberculum/transplanum) defect	Multilayered reconstruction is performed with at least one inlay and one onlay layer FL and fat are the most commonly used inlay materials; double‐layer FL button grafts are considered by some experts A vascularized flap is preferred; a NSF is used when available	35% of experts use a single inlay and 62% use multiple inlay layers When a NSF is unavailable, 75% will consider a intranasal flap (LNWF), whereas 35% will consider an extranasal flap (pericranium vs. TPFF) A significant minority (15%) prefer rigid reconstruction
Anterior cranial fossa (transethmoid/transcribriform) defect	Multilayered reconstruction is preferred with at least one inlay and one onlay layer A vascularized flap is preferred; NSF is used when available When the NSF is unavailable, the pericranial flap is the most common flap used, and free nonmucosal graft onlay with FL is the most common nonvascularized option	Choice of inlay material varies highly 65% prefer two inlay layers and 35% use one layer 67% use a single onlay layer and 30% use two or more layers A few experts would perform dural suturing for inlay repair
Posterior cranial fossa (transclival or craniocervical junction) defect	Multilayered reconstruction is preferred with at least two inlays and one–two onlays Fat and FL are the most common inlay materials; double‐layer FL button grafts are considered by some experts A vascularized flap is preferred; NSF is used when available.	Choice of inlay material varies highly 70% prefer two inlay layers and 30% use one layer 45% use a single onlay layer and 55% use two or more layers When the NSF is unavailable, LNWF, TPFF, or double layer of FL with or without fat is used. A few experts mentioned sphenoid rostral mucosal flaps or dural suturing
Traumatic/Iatrogenic cribriform defects	A single onlay layer with FMG is preferred	Equal preference for a single inlay versus no inlay Choice of inlay material varies 30% of experts will consider NSF for certain indications (e.g., comminuted skull base, high‐flow defects)
Frontal sinus posterior table defects	A single inlay and single onlay is preferred Experts manage medial defects with a purely endoscopic approach, whereas lateral defects are commonly addressed with a graduated endoscopic approach and/or combined open‐endoscopic approach	Choice of inlay material is varied. Equal preference for NSFs and FMGs for onlay reconstruction, depending on defect location Open approaches for lateral defects vary between transorbital techniques, trephination, and osteoplastic flaps
Spontaneous CSF leaks and encephaloceles (cribriform plate, ethmoid roof, SSLR)	A single onlay layer is preferred.	Choice of inlay material is varied, but there is a stronger preference for collagen matrix. 56% prefer one inlay layer versus no inlay Equal preference for NSFs and FMG for onlay repair
Pericranial flap	Pericranial flaps are most often considered for: ACF and suprasellar defects when intranasal flaps are devitalized or not available In the setting of prior irradiation for large ACF/suprasellar defects	A minority of experts will consider pericranial flaps for PCF defects when intranasal flaps are either lost or not available as well as in the setting of prior irradiation Experts diverge with respect to the use of nonmucosal free grafts (i.e., FL) or LNWF versus pericranial flaps for ACF defects with the septum is not available
TPFF	TPFF are most often considered for: PCF and suprasellar defects when intranasal flaps have necrosed or are not available In a previously irradiated field	Experts diverge with respect to the use of TPFF versus LNWF for refractory suprasellar and PCF defects where nonseptal tissue is still available intranasally
Free flap	Free flaps are considered for: Large complex defects PCF and ACF defects in setting of ORN Recurrent postoperative CSF leaks after multiple pedicled flap repair attempts Lack of available pedicled flap options (especially for PCF and craniocervical junction defects)	Free flap donor site varies based on surgeon experience, clinical scenario, and size and location of the defect A few expert teams very rarely, if ever, use a free flap while others have a low threshold for free tissue transfer for large ACF and PCF defects (even for primary reconstruction when other reconstructive options are scarce)
Shunting	Shunting overall is rarely used for surgically created skull base defects unless the patient has a multiply refractory CSF leak or in the setting of IIH for long‐term ICP control	Some experts will consider shunting for multiply refractory CSF leaks regardless of ICP
General principles related to repair techniques	Rigid reconstruction, including gasket seal techniques, is not common for reconstruction of surgically created defects When the septum is unavailable, a LNWF is often considered before using an extranasal flap Vascularized tissue is preferred for high‐flow surgical defects	Inlay materials are highly heterogeneous with FL, collagen matrices, and fat being the most common
Impact of adjuvant treatment on reconstruction	Vascularized flap reconstruction is preferred when there is a history of prior skull base irradiation or anticipated need for adjuvant radiation Chemotherapy generally does not impact the SBR technique	A few expert teams do not change their reconstructive algorithm for patients who may need adjuvant radiation
Lumbar drain	Common indications for LD are: PCF defects, high flow leaks (as defined by the expert team) Recurrent postoperative CSF leak Risk factors for increased ICP Suspected or diagnosed IIH LDs are usually open for 48‐72 h at 5–10 mL per hour	Some experts would also use an LD for large ACF and suprasellar defects A few experts never use an LD A minority of experts consider drainage at >10 mL per hour
Tissue sealants	The majority of experts use dural sealants either always or in specific intraoperative scenarios, such as when a NSF is used or there is a CSF leak Dural sealants are overwhelmingly placed over the final onlay layer	Preferred dural sealants varied between fibrin glue, Duraseal, and Adherus with fibrin glue being the most common Only a few experts prefer fibrin glue placement deep to the onlay
Nasal packing	Most experts use a form of packing Gloved Merocels are the most commonly used nonabsorbable packing, and they are usually removed within a week Nasopore, oxidized cellulose, and gelatin sponge are preferred nonabsorbable packing materials	Some experts will use Vaseline or Xeroform strip gauze instead of gloved Merocels Some experts will keep nonabsorbable packing in place for more than 1 week 17% of experts do not use packing No discernable patterns were elucidated about the impact of defect location on decision to use dissolvable or nondissolvable packing
Postoperative protocols	Nasal and activity precautions are recommended for >4 weeks by most experts 92% do not prohibit straw use 92% administer antibiotics at some time point The majority wait >2 weeks before resuming CPAP The majority of experts hold saline spray to avoid masking a CSF leak	Roughly half of experts use both perioperative and postoperative antibiotics while many other experts will only use them perioperatively or postoperatively Significant variation in timing of starting saline irrigation, the first debridement, initiating CPAP, and resuming air travel.

FIGURE 12.

Graphical depictions of inlay and onlay skull base reconstruction based on defect site, in accordance with the algorithms highlighted in Figures 1, 2, 3, 4, 5, 6, 7, 8, 9, 10. All are sagittal views unless noted otherwise. Original illustrations are adapted from the style of Snyderman et al. [34]. (A) Sellar defect with a “weeping” leak and sellar defect with a visible diaphragm defect with no septum. (B) Sellar defect with visible diaphragm defect with septum. (C) Suprasellar defect. (D) Traumatic or iatrogenic ethmoid defect and spontaneous ethmoid meningoencephalocele/CSF leak. (E) Posterior table of frontal sinus defect. (F) Spontaneous sphenoid (lateral recess) meningoencephalocele/CSF leak (coronal view). (G) Anterior cranial fossa defect with septum. (H) Anterior cranial fossa defect without septum. (I) Posterior cranial fossa defect. Abbreviations: ACF, anterior cranial fossa; ECM, extracellular matrix; ENF, extranasal flap; FL, fascia lata; FMG, free mucosal graft; INF, intranasal flap (excluding nasoseptal flap); NSF, nasoseptal flap; PCF, posterior cranial fossa; PT FS, posterior table of frontal sinus; SS, suprasellar.

The most common indications for choosing autologous reconstruction materials included high‐flow leaks from ACF, SS, and PCF defects. Despite possible donor site morbidity, autologous materials such as FL, fat, muscle, and mucosa are viable reconstructive choices due to their low cost and biocompatibility [18]. Bony autologous materials were used by the minority. In contrast, synthetic grafts are readily available but associated with notable costs, though they appear to have similar rates of reconstructive success and major complication rates compared with autologous grafts [19, 20, 21, 22, 23]. Thus, choice of graft material seems to be based largely on surgeon and institution preferences and availability. The ARS Expert Practice Statement (EPS) on SBR principles (Part 1) and a recent multi‐institutional case‐control analysis assessing high‐flow defects also identified that both autologous and synthetic materials appeared to have comparable outcomes, while donor site morbidity is overall acceptably low if autologous materials are used [23, 24].

In terms of specific inlay materials, collagen matrix is mostly used for “weeping” sellar, ACF, PCF defects, and spontaneous CSF leaks. The adoption of collagen matrix may partly be due to its low cost, availability, ease of use and handling, and avoids the need for a secondary harvest site [22]. Fat was also a popular inlay material as it obliterates dead space and can be easily harvested with low morbidity, but disadvantages can include shrinkage/breakdown, infection, or neurovascular compression [25, 26, 27]. FL is more commonly used as an inlay for large ACF, SS, and PCF defects and has the advantages of excellent wound healing potential, pliability, durability, potential for mucosalization in the nasal cavity, and acceptable donor site morbidity [28, 29]. Synthetic grafts were in the minority of utilized inlay materials, despite their excellent outcomes in the reported literature, which may be related to institutional preferences, availability, and cost considerations [20, 21, 30]. Finally, rigid reconstruction using bone grafts or synthetic plates appears to not be widely used by experts. Rigid reconstruction has known risks of displacement, infection, and injury to neurovascular structures, but has also been shown to be highly effective for inlay repair of high‐flow skull base defects [31, 32, 33]. These discrepancies call for further research to investigate its role.

There is a wide variety in preferences for inlay reconstructive options. There is a lack of consensus on the optimal methods of inlay reconstruction, including the best graft material, placement of graft relative to the dura, graft size relative to the dura, and number of layers. The heterogeneity in the inlay data is likely multifactorial and related to inherent limitations with ESBS research, such as the rarity of skull base pathology and inability to control major confounders like defect size, CSF flow rate, and anatomical limitations. Other factors may include graft material availability at any given center and nuances in defining the layer of graft placement in these complex multidimensional defects. For example, as described earlier, for PCF defects, a common strategy is to use the “epidural tuck” technique, which involves a large FL graft draped over exposed bone and the paraclival carotid arteries, with full coverage of the dural defect, while the edges of the center of the graft are tucked deep to the bone and/or dura and held in place by a fat graft, much like a “gasket seal.” [33, 34, 35] Experts may have interpreted this as an onlay, inlay, or both. It is also important to note that graft material type may not be a significant factor and any inlay material may be sufficient to act as a mechanical barrier for high‐flow defects.

The NSF, known to be reliable and versatile, was by far the most common choice for vascularized reconstruction among experts [36]. The NSF was the preferred option for all defects except weeping sellar and frontal sinus defects. This trend aligns with data showing FMGs and NSFs have similar efficacy in reconstructive outcomes for low‐flow defects, while NSFs have better efficacy for reconstruction of high‐flow defects [37, 38]. The ARS EPS (Part 1) recommended using the NSF as “primary reconstruction of large defects with high‐flow CSF leaks or patients with known risk factors for postoperative CSF leak.” [24] When clinically appropriate, FMGs are a popular onlay choice given low morbidity and ease with harvest, either from a resected middle turbinate or nasal floor [24, 39, 40, 41, 42, 43, 44, 45]. While the standard NSF reliably covers most high‐flow sellar and SS defects, it is critical to be able to rotate and advance the flap enough to cover the superior‐most extent of these detects. This can be achieved by making the anterior septal incision as far anteriorly as possible, and via maneuvers to extend the reach of the flap (e.g., mobilization of pedicle to the sphenopalatine foramen, drilling the sphenoid floor posteriorly, filling the clival recess of the sphenoid sinus with fat). The extended NSF, which also incorporates the nasal floor and inferolateral nasal wall (inferior meatus), is an important alternative especially for larger ACF and PCF defects [46, 47, 48]. Another technical modification brought up by some experts is the nasal floor flap based on the sphenopalatine artery, which effectively creates the substance of the flap using the posterior septum and nasal floor while minimizing the morbidity of denuding the anterior septum [49, 50].

Less commonly employed onlay reconstruction techniques included the middle turbinate flap and “gasket seal” technique. The middle turbinate pedicled flap, which is based off the middle turbinate branch of the sphenopalatine artery, was reportedly used by a few experts, but only for sellar defects with a visible diaphragm hole and SS defects. Overall, the low popularity of the middle turbinate flap is likely due to its small surface area, limited arc of rotation, tedious harvest, and thin mucosa; given these restraints, this flap is thought to be most applicable for cribriform, sellar, and small SS defects. The LNWF can be used in similar situations with the advantages of increased tissue bulk, easier harvest, and longer rotation arc [37, 46, 51, 52, 53, 54, 55, 56, 57, 58, 59]. Additionally, the “gasket seal” technique, which is a nonvascularized reconstruction, involves anchoring onlay placement over the central part of a larger graft with both sub/epidural inlay and peripheral onlay components. This can provide a reliable and long‐term watertight closure for cranial base defects [33, 60, 61].

An important trend to discuss is the increasing number of reconstructive layers as defects increase in size, complexity, and frequency of communication with a cistern or ventricle. The frequency of two or more onlay layers increased from 2.5% for sellar defects with visible diaphragm hole to 25% for SS defects, 30% for ACF defects, and 55% for PCF defects. Similarly, the frequency of two or more inlay layers increased from 60% for sellar defects with a visible diaphragm hole to 70% for PCF defects. Thus, most experts are using roughly four layers to reconstruct PCF defects, which highlights the difficult nature of PCF reconstruction and high risk of postoperative CSF leak [62, 63, 64, 65].

4.2. Sellar Defects

Sellar defects, primarily following surgical treatment of pituitary adenomas and Rathke cleft cysts, exist on a spectrum first classified by Esposito et al. [16]: no CSF leak with a descended diaphragma (grade 0); a “weeping” low‐flow defect without a visible diaphragma hole (grade 1); active CSF leak through a visible hole in the diaphragma (grade 2); and a large dural defect with possible communication with the third ventricle or SS cistern (grade 3). Table 6 summarizes common themes and the main points of divergence between expert teams for sellar reconstruction. For weeping sellar defects, experts predominantly utilize a single inlay and onlay, although a quarter of experts utilize two or more inlay layers. Inlay materials varied heavily and included both synthetic and autologous materials. These grafts were predominantly placed deep to the sellar dura, although a smaller number do place collagen matrix or FL in the epidural layer. Additionally, experts utilize a single FMG onlay (57.5%) more commonly than a NSF (35%). When the septum is unavailable, experts almost always prefer a FMG (85%) rather than another vascularized flap.

For larger sellar defects with a visible defect through the diaphragma, 60% of experts prefer two or more inlay layers while the other 40% use a single inlay. Experts again use a wide variety of materials for inlay reconstruction; fat and collagen matrix were most common, but ECM‐based/synthetic scaffolds, hemostatic materials, FL, and rigid buttresses are also used. In terms of onlay repair, experts prefer the NSF over FMG. In the absence of NSF availability, most experts would consider a FMG (75%) while 47.5% would also consider another intranasal flap such as the LNWF, and 12.5% would use a free nonmucosal graft like FL.

Endoscopic repair of sellar defects is understandably highly variable in the published literature; the number of layers and materials used may depend heavily on the size of the defect, presence or absence of a CSF leak, and institutional/surgeon preference. For weeping sellar defects, several successful techniques (<5% postoperative CSF leak rates) have been described including clipping of exposed diaphragma edges, sellar dural suturing, single inlay synthetic graft without an onlay, and multilayered repair with hemostatic materials and/or fat in the sella, subdural or epidural collagen matrix or FL, rigid buttresses, FMG or NSF onlay, and/or a dural sealant [5, 52, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76]. It is clear that most experts use at least one inlay and onlay layer for repair of weeping defects with only 12.5% not using an inlay and 7.5% not using an onlay. The inlay material is highly heterogeneous with fat, hemostatic materials, and collagen matrix being the most common. It is plausible that fat is common given its ability to obliterate the sellar dead space and apply gentle counterpressure against the diaphragma sella where the seepage occurs. Collagen matrix may be often used in addition to fat to prevent fat migration and further bolster the repair and may also be used in place of fat due to its low cost, availability, and to avoid donor site morbidity [22]. A recent simplified and theoretically less morbid algorithm for sellar reconstruction published by Chaskes et al. [52] showed a 1.7% postoperative CSF leak rate among 347 patients with weeping sellar defects who were reconstructed with a single subdural collagen matrix with dural sealant and without an onlay. This raises the question of how many layers are truly necessary for repairing weeping defects and if the added morbidity of harvesting autologous tissues outweigh their potential benefit for increasing reconstructive integrity [52]. At least one inlay layer is likely necessary for repair of weeping sellar defects, and the necessity of a mucosal onlay has been questioned [52]. However, almost all experts use an onlay FMG, and no study has systematically evaluated the efficacy of a single onlay without inlay repair.

An interesting phenomenon is the delayed postoperative CSF leak after a transsphenoidal surgery during which no intraoperative CSF leak was identified. A recent study by Kshirsagar et al. [77] describes rapid ICP shifts from straining, improper postoperative precautions or compliance, and rupture of or trauma to a thinned descended diaphragma as potential culprits. Some surgeons may consider prophylactic onlay coverage in cases which there was significant SS extension of tumor with a resultant thinned diaphragma or obliteration of the sellar with collagen matrix to protect the diaphragma from rough bony sellar edges even in the absence of a leak; however, this is counter to the goals of Rathke's cleft cyst surgery for which marsupialization is crucial [77].

For larger sellar defects with arachnoid violation and cistern or ventricle communication, the literature is more consistent in terms of the necessity for multilayered reconstruction that involves an onlay vascularized flap [37]. Yet again, the inlays used are heterogeneous and may have similar efficacy profiles [5, 52, 72, 74, 76, 78]. Interestingly, when the septum is absent, most experts (75%) would consider nonvascularized FMGs, likely due to sellar defects being relatively smaller in size, with generally favorable bony edges and contour for inlay and onlay placement. An important addition is that 47.5% of experts still consider a non‐NSF intranasal pedicled flap like the LNWF, presumably to maintain the principle of needing vascularized tissue. First described by Hao et al. in 2004, the LNWF has emerged as an important addition to the skull base surgeon's arsenal when the septum is unavailable and the added morbidity and time requirement for extranasal flaps may not be required [36, 56, 57, 58, 59, 79]. Lavigne et al. reported the successful use of the LNWFs for repair of six sellar/SS defects with only one requiring repositioning due to postoperative leak.58 Overall, the literature on non‐NSF intranasal flaps for sellar defects is scarce and the success rates vary [57, 58, 59]. Drawbacks of the LNWF include its relatively small surface area, limited arc of rotation, and the tissue memory of the conchal portion of the flap surface that could lead to failure and necessitate postoperative flap repositioning [37, 57, 58]. Extensions of the LNWF that incorporate additional mucosa from the nasal floor and anterior nasal septum can provide additional surface area and greater reach in special circumstances [56]. Experts seem to also defer using extranasal pedicled flaps like TPFF or pericranial flaps for these defects, presumably because their added benefit for augmenting reconstruction relative to free grafting may be outweighed by the added morbidity and effort of flap harvest and tunneling.

4.3. Sup/Transplanum/Transtuberculum Defect Reconstruction

SS defects in ESBS present several challenges for repair given the direct communication with the SS cistern and, oftentimes, the third ventricle: the need to address a large dead space while taking care to not compress the optic apparatus, superior hypophyseal arteries, or infundibulum; and technical skill required to place inlays anteriorly [5, 25, 29, 80, 81]. Roughly two‐thirds of experts use at least two inlay layers while the other third use a single inlay. Additionally, 75% of experts use a single onlay while a quarter use two or more layers. Table 6 summarizes common themes and the main points of divergence between the expert teams for SS reconstruction.

In terms of inlay technique, experts use heterogeneous materials in variable relation to the dura as is common in all SBR after tumor resection. Autologous tissues like FL and fat are more common than collagen matrix and other synthetic materials. While differences in FL versus collagen matrix usage may reflect surgeon preference or geographic trends, the common usage of subdural fat amongst experts is notable and may be related to the large dead space seen with SS defects. Other possibilities are that experts may have more easily accessible fat tissue from the same field given their frequent utilization of FL. Fat has been shown to be safe and effective as part of SS reconstructions, although not always necessary even with a large dead space [25, 29, 80, 82, 83, 84]. There is risk, however, of optic nerve/chiasm compression from too much fat placement. The high success rate is partly attributable to the “button graft” technique, which is used by 12.5% of experts. First described in 2010, button grafts are made by suturing two layers of FL or collagen matrix together in their centers such that the inner and outer layers are 25 and 5–10% larger than the dural defect, respectively. The button acts as a plug against CSF egress with a lower risk of subdural graft migration [82]. The inner and outer layers can be placed as inlays or both inlay and onlay. Other advantages of the button graft are the ability to avoid subarachnoid fat placement and LD placement [82]. Several retrospective series and case reports show that FL button grafts are effective at addressing high‐flow intraoperative CSF leaks with or without NSF [29, 80, 82, 83, 84]. Nevertheless, the main theme for inlay reconstruction seems to be at least two layers consisting of FL or collagen matrix, sometimes as a button graft, with or without subdural fat.

Onlay reconstruction for SS defects is similar to high‐flow sellar defects but with a greater emphasis on vascularized tissue. A NSF is used by all experts (100%), usually as a single layer, with a few teams considering FL or synthetic grafts deep to the NSF. This aligns with several studies showing low postoperative CSF leak rates with a NSF for SS defects as well as the ICSB, which recommends multilayered reconstruction (without specifying inlay materials) and pedicled flaps for SS defects [5, 60, 62, 65, 80, 83, 85, 86]. When the septum is not available, 75% of experts would consider a non‐NSF intranasal flap, with the LNWF being the most common (60%). Other options included extranasal vascularized flaps (35%) such as the TPFF (15%) and pericranial flap (20%), FL or other free nonmucosal grafts (30%), and FMGs (22.5%).

The preference for using LNWF to reconstruct SS defects when no NSF is available may be higher than predicted given a prior cadaveric study by Harvey et al. [37] showing that LNWFs are only able to cover 52–84% of ACF defects but can actually provide more mucosa than is necessary to cover PCF defects (i.e., more than 100%); however, the LNWF can be expanded to include the anterosuperior lateral nasal wall as well as the nasal floor and septum medially [37]. However, modifications to the LNWF have extended its reach since the time of this publication [57]. Retrospective series on using LNWFs for large dural defect repairs also predominantly have patients with clival or sellar pathology but few patients with SS defects [46, 57, 58, 59]. Given the high reported awareness of LNWF for SS defects among experts, this represents an opportunity for future cohort studies or a meta‐analysis as a potential way to reduce extranasal pedicled flap use and its associated morbidity for the appropriate SS defect [5, 87, 88].

The relatively high prevalence of FMG in the absence of NSFs is an important note given the preference of vascularized tissue over FMGs for high‐flow CSF leaks [38, 89]. It is possible that a FMG is used alongside another onlay layer, such as FL, in the absence of the NSF given that 25% of experts use two or more onlay layers. Thus, it appears that for onlay reconstruction of SS defects, experts consider a NSF; if the septum is unavailable, alternative options are non‐NSF intranasal flaps or extranasal pedicled flaps.

4.4. Anterior Cranial Fossa/Transcribriform Defect Reconstruction

ACF defects, which are commonly encountered from resection of primary sinonasal malignancies (e.g., olfactory neuroblastomas) or intracranial neoplasms (e.g., olfactory groove meningiomas), can be quite large and span from orbit to orbit and from the posterior table of the frontal sinus to the planum sphenoidale, which poses a reconstructive challenge due to the size of the defect [90]. This is especially true when placing inlays anterior to the defect along the contour of the vertically oriented posterior table as it transitions to the horizontally oriented ethmoid roof, as well as achieving enough anterior reach with the NSF. Accordingly, postoperative CSF leak rates after ESBS for olfactory groove meningiomas have been reportedly high [5, 65, 91, 92]. With larger tumors, the large intradural cavity remaining after tumor removal makes it difficult to anchor an intradural inlay graft. Many surgeons advocate for a low threshold for a transcranial approach, indications being large ACF tumor size, risk of frontal lobe sagging with ESBS, and high incidence of anosmia unless a unilateral, olfactory recess‐preserving, approach is used [93, 94, 95, 96]. However, ESBS for ACF pathology has the benefits of early devascularization of the tumor, improved visualization, and minimal frontal lobe retraction [5, 65, 80]. Recent series also report improved multilayered reconstructive techniques with postoperative CSF leak rates that rival the transcranial approach as well as minimal frontal lobe sagging [33, 61, 80, 91, 97]. Postoperative CSF leak rates for other ACF pathologies, namely, olfactory neuroblastomas, have been more favorable [98, 99, 100, 101].

Table 6 summarizes common themes and the main points of divergence between the expert teams for ACF reconstruction. For inlay reconstruction, two‐thirds of experts use two or more layers (65%) for ACF defects. Experts predominantly use collagen matrix (45% subdural, 17.5% epidural) and FL (35% subdural, 47.5% epidural). A minority of experts also place fat (25% subdural, 7.5% epidural) and ECM‐based scaffolds (10% subdural, 15% epidural). A recent multi‐institutional European analysis of 940 ESBS defect repairs highlighted that multilayered reconstruction with fewer than three layers may afford a higher postoperative CSF leak rate [102]. Eloy et al. reported a series of 10 patients who underwent three‐layer repair of transcribriform defects using a subdural FL inlay, combination inlay‐onlay acellular dermal allograft that is placed within the epidural space using gelatin sponge and then draped over exposed bone, followed by a pedicled NSF, with no postoperative CSF leaks [20, 80, 103]. Mattavelli et al. [101] published a retrospective series of 186 patients, the largest to date, who underwent triple‐layer FL repair of ACF defects with a postoperative CSF leak rate of 5.8% and overall complication rate of 9.7%. While the NSF onlay undoubtedly contributed to successful repair, a multilayered inlay repair with careful attention to full dural defect coverage and creation of a “water tight” seal is likely important. The optimal material, namely collagen matrix or FL with or without inlay fat, is highly debated. Although retrospective series exist that compare or advocate for either material, no direct comparisons have been made [28, 29, 30, 91]. Fat is beneficial for eliminating dead space and preventing pooling of a large CSF reservoir although there is a risk of fat herniation through the repair as the compressed bran re‐expands. Future studies will help answer whether the added cost of synthetic materials is justified when considering the low donor site morbidity and limited increase in surgical time seen with FL [19, 28, 29, 104].

Most experts (67.5%) use a single layer while 30% use two or more layers for onlay reconstruction. When the septum is available, experts most often use a NSF (92.5%). It is notable that 22.5% of experts would also consider a free nonmucosal graft onlay (i.e., FL). This is likely a separate onlay layer used deep to the NSF when FL is already harvested for the inlay, or a combo inlay‐onlay layer as described previously [20, 80]. When the septum is unavailable, the outcomes were more heterogeneous, with most experts utilizing a pericranial flap (60%), non‐NSF intranasal flap (27.5% overall, 20% LNWF), or FL (27.5%). Pericranial flaps are a workhorse for ACF reconstruction in the absence of intranasal vascularized tissue given its robust tissue bulk, excellent anterior coverage with reach as posterior as the clivus in certain cases, and ability to tunnel the flap through the nasion or frontal sinus posterior table entirely extracranially via a Draf 3 approach [87, 88, 105, 106, 107, 108]. FL onlay may be used for ACF defects when no vascularized options are available, and its larger size and excellent healing potential is beneficial with such defects; however, given the size and complexity of ACF defects, it is clear that most experts prefer vascularized tissue first‐line when available [29, 109]. The relative low frequency of non‐NSF intranasal flaps is likely due to their limited ability to extend anterior enough to cover the posterior table or anterior ethmoid roof or provide adequate coverage of large defects, as is true even with extended NSFs [47]. The minority of experts who do use a LNWF may combine them with other flaps such as the septal flip flap supplied by the anterior ethmoid artery or anteriorly‐based inferior turbinate flap [110, 111, 112].

Thus, overall, the most endorsed repair technique for ACF defects is a multilayered reconstruction: FL or collagen matrix for the inlay as well as a NSF, pericranial flap (if the septum is unavailable), or FL for the onlay, albeit the number of layers may vary.

4.5. Clival/Posterior Cranial Fossa Defect Reconstruction

Repair of PCF defects varied the most among experts relative to all other defect locations. This may not be entirely surprising given the technically challenging nature of reconstruction in this location attributable to an anatomically narrow corridor limited laterally by the carotid arteries, high‐flow CSF from the prepontine cistern, frequent lack of bony edges and dura for inlay placement, and interdural course of the abducens nerve [62, 65]. Less experience with repairing this defect type and gross total resection of chordomas with intradural dissection, relative to subtotal resection, may afford higher postoperative CSF leak rates [5, 65].

Accordingly, Table 6 summarizes common themes and the main points of divergence between expert teams for PCF reconstruction. Seventy percent of experts in this study used at least two inlay layers to repair PCF defects, which is the highest rate of any defect location. Inlay material type was again highly heterogeneous among experts. Common inlay materials used by were fat, (55% subdural vs. 20% epidural), collagen matrix (15.0% epidural vs. 37.5% subdural), and FL (12.5% subdural vs. 37.5% epidural). Ten percent of experts use subdural‐onlay FL button grafts. ECM‐based scaffolds (7.5–12.5%) and rigid inlay repair (15%) were less common. Therefore, fat was the most common material used, and this is an important distinction that may highlight a focus for further research, as fat can help eliminate dead space, promote scar formation, provide a platform for additional inlay or onlay graft placement, and prevent postoperative pontine encephaloceles [65, 113]. Additionally, the heterogeneity in inlay graft types used by experts may allude to possibly similar efficacies for CSF leak repair and may be explained by the lack of consensus or high quality evidence comparing inlay materials for high‐flow defects as discussed previously. As discussed above, the “epidural tuck” technique is commonly utilized to reconstruct these challenging defects, with the epidural/onlay layer consisting of both autologous (e.g., FL) or synthetic (e.g., acellular dermal matrix) grafts. In this area, the abducens nerve may be released from Dorello's canal or the basilar plexus and exposed due to tumor bony erosion and/or resection, and care must be undertaken to avoid injury while placing layers of reconstruction.

Many authors advocate for a low threshold to use a NSF onlay given its long arc of pedicle rotation if needed (i.e., for clival defects that are typically deep), adaptability in size with option to extend onto the nasal floor and inferior meatus, and superior efficacy over free grafts for high‐flow CSF leaks [5, 37, 59, 86]. Consistent with this, 95% of experts reported a preference using a NSF for onlay repair of PCF defects. It is also notable that 20% of experts use an additional layer of FL under the NSF. Despite the diversity in inlay repair, onlay reconstruction seems to be uniform among experts. In contrast, a largely unstudied scenario, however, is how to repair defects in this location when the septum is no longer available due to oncologic resection or prior surgery. This is showcased by the significant heterogeneity in interview answers for onlay repair with no available septum. A majority of experts (65%) considered another intranasal pedicled flap (i.e., LNWF) and 55% considered an extranasal pedicled flap (i.e., TPFF). Currently, there are no studies comparing extranasal versus intranasal pedicled flaps for repair of PCF defects and no strong recommendation about one over the other can be made from the expert data. Utilization of either option may be due to surgeon preference, concern for prior or anticipated radiation, defect size, and availability of sinonasal tissue after resection [114]. However, recent literature suggests prior radiation may not impact reconstructive success when vascularized local flaps are used [115]. Interestingly, 12.5% of experts would still consider a FMG and 27.5% endorsed free FL. Soudry et al. [86] reported a success rate of 60% for preventing postoperative CSF leak with free grafts compared with 75–100% success with vascularized flaps for clival defects. Although a small number of experts consider free grafting when the septum is unavailable, it is notable that 55% of interviewees advocate for at least two onlay layers, which is the highest rate among all defects. Few experts likely use a single free graft onlay for repair of high‐flow PCF defects; rather, free grafts are likely an adjunct to a pedicled flap especially when the defect size does not allow for full coverage solely with a non‐NSF intranasal flap (“supercharging”) [116]. In a last resort scenario, free grafts may be considered by experts in isolation if the multilayered inlay repair is felt to be highly effective at creating a “watertight” closure without further visualized egress of CSF, other intranasal flap options are not available, and extranasal pedicled flaps do not reach to fully cover the defect.

4.6. Reconstruction Options for Refractory CSF Leaks

Reconstruction of surgically created CSF leaks that have failed multiple prior repairs poses a highly challenging problem for surgeons. Outcomes may depend on surgeon experience, reconstructive options, exposure of critical neurovascular structures (e.g., internal carotid artery, optic nerve), comorbidities that impact wound healing (e.g., nutritional status, uncontrolled diabetes, immunosuppression, smoking), available autologous tissues, elevated ICP, patient characteristics like body‐mass index (BMI) and poor compliance with postoperative instructions and precautions, tumor histopathology, defect size and location, history of irradiation, and anticipated need for adjuvant treatment [5, 24, 62, 63, 87, 117]. Intranasal pedicled flaps like the NSF and LNWF are first‐ and second‐line options for onlay reconstruction but may not be available or large enough due to tumor involvement of the donor tissue, defect size and location, or flap necrosis/failure. In such situations, pedicled extranasal flaps, such as the pericranial flap and TPFF, along with free flaps to a lesser extent, are employed with high success rates at preventing postoperative CSF leak even in previously irradiated fields [46, 63, 87, 88, 118]. Pericranial flaps are traditionally utilized for ACF and SS defects, whereas the TPFF is more often used for sellar and PCF defects; this is likely related to each flap's arc of rotation (i.e., pericranial flap from anterior to posterior with more reach to superior defects; TPFF from lateral to medial and more reach to clivus) [34, 87]. Additional length can be achieved for the pericranial flap by raising it to the occiput, which requires back elevation of the scalp. However, there is limited consensus or high‐quality evidence comparing the efficacy of each extranasal flap for sealing refractory leaks. The present study pools the experiences of experts in hopes of achieving a general framework for approaching these challenging defects with refractory postoperative CSF leaks. Table 6 summarizes common themes and the main points of divergence between expert teams for use of pericranial flaps, TPFFs, free flaps, and shunting for multiply refractory postoperative leaks.

Overall, experts recommended pericranial flaps after lack of availability or loss of intranasal pedicled flaps especially for ACF and SS defects and previously irradiated fields. This highlights experts’ beliefs that vascularized tissue for large dural defects with active CSF leak are likely more effective than free grafts like FL that could still be harvested in this situation. Several retrospective studies have highlighted the success of pericranial flaps for reconstruction of ACF and SS defects, and this vascularized flap will serve as a crucial option in surgeons’ armamentarium when intranasal tissues are unusable [46, 88, 106]. Notably, no experts explicitly mentioned refractory PCF defect repair with pericranial flaps when asked the open‐ended question about management of refractory leaks (Figure S1), but 10% of experts did report using pericranial flaps when asked specifically about PCF defects (Figure 5). Gode et al. described their experience with pericranial flaps for seven refractory PCF defects with exposed critical neurovascular structures; four patients had immediate success with sealing the CSF leak while the other three patients had delayed resolution of leakage with conservative measures with no patients requiring further reconstruction.87 Patel et al. and Torres‐Bayona et al. also reported success with the pericranial flap for clival reconstruction [63, 88]. The pericranial flap may be an underutilized and potentially advantageous resource for difficult clival defects despite some concerns that its length may not reach the inferior clivus, especially since the pericranial flap is easily raised through a coronal incision and has been modified to be tunneled extracranially [87, 88, 119]. However, PCF repairs with pericranial flaps are technically very challenging and require significant surgeon experience with a higher risk of distal flap necrosis given a flap length requirement of up to 18–20 cm, with occipital scalp back elevation permitted for extension of the flap length [88].

Experts recommended TPFFs when intranasal flaps have necrosed or are not available, especially for PCF and SS defects and in a previously irradiated field. The TPFF was first described for endoscopic skull base applications in 2007 and requires tunneling through the infratemporal fossa (ITF) and pterygopalatine fossa (PPF) into the nasal cavity, namely for middle cranial fossa and PCF fossa defects [56, 120, 121]. Figure 5 shows that 40% of experts would use TPFF if a NSF was not available. Interestingly, three experts would only use a TPFF if a pericranial flap was unavailable, highlighting relative preferences for these two robust extracranial flaps and perhaps slower adoption of the TPFF for ESBS. This may be due to the fact that the TPFF was more recently introduced to ESBS, carries technical demand and requires meticulous harvest with dissection through the ITF, and necessitates extra external incisions [56, 88, 122]. Despite the drawbacks of TPFF, its vascular caliber is larger than the pericranial flap and its pedicle length is up to 17 cm [123, 124]. A cadaveric study by Siu et al. [122] showed TPFF can reliably cover the entire clivus as well as the cribriform plate or planum sphenoidale when at least 12 cm long. Notable modern adaptations of this flap involve a supraorbital “side door” tunnel via a pterional craniotomy for coverage of ACF defects with supraorbital extension that reduces the risk of pedicle kinking through the PPF as well as inclusion of deep temporalis fascia, pericranium, and a strip of temporalis muscle for more robust coverage [118, 120, 123, 124, 125]. Small retrospective series have also highlighted its ability to repair large dural defects of the ACF and PCF [118, 123]. Accordingly, TPFF is a versatile flap with the ability to cover heterogeneous complex defects in variable locations, and most experts currently utilize them in a more traditional fashion for the PCF and SS areas with an increased predilection for usage in a previously irradiated field.

In rare challenging situations, over half of experts also consider free tissue transfer from various donor sites. The most common indications included large complex defects (concurrent orbital exenteration or maxillectomy), PCF and ACF defects due to ORN, recurrent postoperative CSF leaks after multiple intranasal or extranasal pedicled flap repair attempts, and lack of available pedicled flap options due to oncologic resection (especially for the PCF and craniocervical junction, and less commonly ACF). Several studies have highlighted the advantages of free tissue transfer for SBR, including a robust vascular supply especially in previously irradiated fields, plentiful tissue bulk that can withstand adjuvant radiation, heterogeneous tissue type availability including skin, muscle, fascia, fat, and bone, and lack of exposure to prior surgical trauma or radiation [126, 127, 128, 129, 130, 131, 132]. While free flaps for SBR traditionally involved large open approaches, several novel techniques for endoscopic pedicle tunneling and local pedicle options are now described to limit operative morbidity [128, 131, 132, 133]. On the other hand, free tissue transfer is technically challenging especially in the narrow operative corridor of the anterior skull base with endoscopic approaches, introduces donor site morbidity, has a small but significant risk of vascular thrombosis with flap loss, and may make postoperative imaging surveillance more difficult [128, 134].

Despite these challenges, several case reports and small retrospective cohorts have demonstrated the feasibility and relatively low complication rates associated with free flap reconstruction of ACF and PCF defects [127, 129, 134, 135]. PCF defects were the most common subsite reconstructed with free flaps by experts likely due to the high risk nature of prepontine cistern communication, posteroinferior extension into pharyngeal mucosa, exposure of critical neurovascular structures, lack of bony edges for proper multilayered reconstruction, lack of pedicled flap bulk to prevent gravity‐dependent CSF seepage, and inability of pedicled flaps to span the entire defect. ORN defects are perhaps the most challenging defects to repair given the lack of healthy surrounding vascularized tissue, large defect size, and concurrent infection. Flaps incorporating muscle, such as vastus lateralis or serratus anterior flaps, may provide needed tissue bulk in these situations but at times may be too large to tunnel into the defect [132]. After failure of multimodality therapy with serial debridements, medical therapy, and/or hyperbaric oxygen, anterolateral thigh and radial forearm free flaps have been shown to successfully and longitudinally address expansive osteoradionecrotic skull base defects to prevent dangerous neurologic sequelae when even large extranasal pedicled flaps like the pericranial flap fail. Some authors advocate for a low threshold to consider free tissue transfer in the setting of extensive skull base ORN [126, 127, 129, 132, 135, 136, 137].

Finally, shunting was considered by only five (12.5%) expert teams for multiply refractory CSF leaks independent of ICP. However, over half of expert teams consider shunting when persistently elevated ICP or IIH is suspected as a contributor to refractory postoperative leaks. These findings suggest that shunting for all refractory skull base defects related to tumor resection has fallen out of favor over time. The role of permanent CSF diversion may be more crucial for preoperative hydrocephalus, IIH, and spontaneous skull base defects, for which the risk of postoperative CSF leak is higher and additional spontaneous defects may occur in the future [109, 138, 139, 140]. Shunting is also a formidable option if patients are unable to tolerate long‐term medical therapy with acetazolamide or medications that reduce CSF production and the risk of postoperative spontaneous CSF leak [109, 141, 142, 143]. Nevertheless, it was likely not common to use shunts for refractory skull base defect leaks in the absence of elevated ICP given there is limited evidence to suggest its benefit in this situation when ICP is normal. Although CSF flow through the surgically created fistula can be reduced, the defect remains unclosed and the risk of ascending meningitis and pneumocephalus persist. Additionally, permanent CSF diversion is associated with relatively high rates of major and minor complications and obstruction requiring shunt revision, with some patients requesting shunt removal after resolution of the leak [142].

4.7. Specific Reconstruction Techniques

Although the following techniques were only utilized by a few experts, the qualitative interviews highlighted several unique techniques and adjuncts to multilayered SBR. Based on numerous reports, preservation, elevation, and replacement of sphenoid mucosal flaps over sellar defects for low‐flow leaks can achieve a balance of improved wound healing and favorable reconstructive outcomes [144, 145, 146]. Endoscopic clipping of diaphragma sellar arachnoid defects has also been described previously [66, 147]. Generally, this technique involves careful preservation and identification of diaphragma edges during transsphenoidal pituitary surgery, gentle grasping of one diaphragma edge with a suction or grasping forcep in the nondominant hand so as to oppose it against the other free diaphragma edge, and finally clipping the opposing diaphragma edges together using a nonpenetrating manually‐applied clip. Sun et al. [147] and Kim et al. [66] described series of 21 and 144 patients, respectively, who underwent primary clipping of diaphragma defects with grades 1–3 CSF leaks during transsphenoidal pituitary surgery and reported very low postoperative CSF leak rates (4.7 and 2.8%, respectively). No studies to date have directly compared these techniques to various other repair methods for endoscopic pituitary surgery, although many published reconstructive methodologies demonstrate high success rates (see above discussion on sellar defects).

Similarly, several techniques and apparatuses have been adapted to perform endoscopic dural suturing, either for primary dural closure when opposing edges are present or an interposition synthetic or autologous inlay graft [67, 68, 69, 70, 71, 148]. The main advantage is the ability to bridge a large defect and reduce it down to a natural suture line, which tends to require a much smaller surface for healing. This technique is associated with outstanding outcomes and has been adapted for numerous defect types, although it is highly technical and may require the use of specialized sutures [149]. A similar technique involving suture closure of the rostral mucosa following surgery of the PCF has also been reported [146, 150].

Surgeons have also employed hydroxyapatite cement as a rigid onlay to seal skull base defects, and this technique has been reported with excellent outcomes for high‐flow CSF leak repair [151, 152, 153, 154]. A recent study of 97 Esposito grades 2 and 3 intraoperative CSF leaks were uniformly repaired with no postoperative CSF leaks using this technique, which included a NSF onlay on top of the hydroxyapatite cement [153]. Despite being a foreign material, the published studies reported no allergic reactions or infections related to hydroxyapatite use [154]. One drawback about this technique, however, is the cement can be challenging to remove if revision surgery is required.

4.8. Effect of Radiation Therapy and Chemotherapy on Reconstruction Technique

Radiation treatment is recognized to produce mucosal inflammation and prolong wound healing, thereby increasing the risk of reconstructive failure. Although most experts reported escalating their reconstructive strategy (e.g., utilizing a vascularized flap in a postradiated case when a free graft may be appropriate for primary cases) in order to compensate for this risk, recent evidence appears to suggest that the overall impact of postirradiated tissues on SBR outcomes is limited [90, 115]. Furthermore, timing of adjuvant radiation therapy before or after the 6 week postoperative mark also does not appear to compromise reconstructive outcomes [155], though many experts would likewise “step up” the reconstructive algorithm in anticipation of possible radiation‐induced effects. On the other hand, the presence of radiation necrosis of the skull base represents the most severe of cases, which may indeed require the most aggressive of reconstructive options given poor blood supply at the wound bed. There are currently no studies dedicated to the effect of chemotherapy on wound healing of the skull base, which may explain why it is generally not a factor for changes in reconstructive algorithm.

4.9. Diagnosis and Management of Early Postoperative CSF Leaks

Identification of a postoperative CSF leak can be challenging and often requires a high degree of suspicion with acknowledgement of risk factors, attention to the patient's clinical course and risk factors, and thorough diagnostic evaluation [62, 90, 117, 156]. To evaluate for postoperative CSF leaks, interviewed experts most commonly employed CT imaging to detect increasing pneumocephalus or localize a skull base defect as well as provocative tilt testing to observe clear rhinorrhea (Figure 11). Roughly a quarter of experts also consider patient symptoms, beta‐2 transferrin/beta‐trace protein testing, bedside endoscopy, or urgent exploration in the operating room (20–25%). Intrathecal fluorescein use was not as common at 10%, which may be secondary to many patients not having a LD postoperatively.

Imaging is likely not necessary on a routine basis [157, 158], but in patients with suspicious symptoms, it offers a formidable sensitivity and can correlate pathologic or evolving pneumocephalus with true postoperative CSF leakage [157, 158, 159]. An emerging body of literature demonstrates that common signs and symptoms of CSF rhinorrhea, such as clear rhinorrhea, nausea/vomiting, “halo” sign, or headache, have poor positive and negative predictive values for CSF leak and must be supplemented with objective evaluation techniques [117, 160]. Naturally, the presence of meningitis is more concerning and predictive [161]. Provocative tilt testing, especially when negative, also has a poor association with true postoperative CSF leakage [90]. A lack of response to ipratropium bromide nasal spray may be a novel method of discerning patients with true CSF rhinorrhea in the preoperative setting [162], although its applicability to postoperative skull base patients is unknown. A minority of experts use beta‐2 transferrin/beta‐trace protein testing in the postoperative setting, which may be due to limited access to point of care testing, extended time needed for test results, and the fact that beta‐trace protein is only available in Europe. Additionally, beta‐2 transferrin testing may not impact clinical care for a highly suspicious true postoperative leak that typically requires more urgent intervention [163]. The amount of fluid necessary for adequate beta‐2 transferrin testing may also be difficult to collect [164, 165, 166, 167]. Conversely, beta‐trace protein testing is quite sensitive, only requiring 5 µL of CSF in 1 mL of nasal secretions, and can result in less than 1 h with an affordable cost [168, 169, 170]. Currently, there are limited data assessing the utility of bedside endoscopy versus upfront exploration in the operating room for diagnosing CSF leak; such decisions largely vary by surgeon and institutional protocols. As such, a few experts mentioned attempting packing removal and repositioning the reconstruction at bedside while many others stated that they only attempt this in the operating room.

Ultimately, most experts managed postoperative CSF leaks with urgent exploration and revision reconstruction in the operating room (77.5%) compared with 32.5% managing conservatively with bedrest and LD placement. Among experts who specified, those who choose urgent exploration will do so either immediately or on the same day. Experts likely weighed several important factors when deciding their management, including whether a postoperative LD is already in place, if the LD was open or clamped, the patient's neurologic and medical status, the timing of the leak, the intraoperative leak flow rate and defect size, confidence of intraoperative repair, and the patient's risk factors for postoperative CSF leak. Most surgeons likely prefer operative exploration because it has both diagnostic and therapeutic value, may shorten hospital stays, and reduce the risk of postoperative and LD‐related complications [5, 171]. Some postoperative leaks fail LD trials and may require operative revision regardless. In patients who are clinically stable and/or have had a robust intraoperative repair (i.e., no intracranial air entry potential), conservative management can be considered to avoid operative intervention.

4.10. Dural Sealants

Dural or tissue sealants are commonly utilized in ESBS in order to augment reconstruction, and most experts (76.3%) reported using this in their practices with varied patterns (Tables 1 and 6). Fibrin glue (35%) was the most commonly used sealant, followed by Duraseal (27.5%) and Adherus (20%), which may reflect surgeon preference and/or institutional availability and cost concerns. A recent systematic review and meta‐analysis by Pang et al. [172] showed no apparent differences in postoperative CSF leak between various sealants and whether or not sealant was used for various defects. Furthermore, the ARS EPS (Part 1) corroborated that sealants may be considered as an option for supporting the reconstruction, but that most data supporting use are based on in vitro evidence and has not clearly translated to clinical outcomes [24]. An interesting finding is that two experts reported using sealants underneath the final onlay, though this is thought to be fibrin glue only. There is a theoretical concern that if the sealant is placed between the inlay and onlay layers, it may prevent appropriate healing due to the lack of direct contact of the onlay to the underlying bone or tissue. Conversely, 23.7% of experts reported never using a tissue sealant. This is consistent with a recent large‐sample prospective study and a meta‐analysis that found no apparent benefit in SBR outcomes with dural sealants in light of its relatively high costs, echoing findings from a prior smaller retrospective study [172, 173, 174]. In contrast, a recent multi‐institutional study identified a benefit in PCF reconstruction outcomes with sealant use [90]. Further studies will be necessary to investigate its true utility for ESBS.

4.11. Nasal Packing

Most experts use dissolvable (73.3%) and nondissolvable (82.5%) packing (Tables 2 and 6). Similar to reconstruction layers, options for nasal packing were not mutually exclusive and surgeons may use multiple methods for the same defect. Nasopore/Hemopore (Stryker, Kalamazoo) were the most common absorbable packing material, whereas all other materials were used by less than half of experts. Oxidized cellulose and hemostatic slurries like Surgiflo are used by no more than a quarter of the cohort. Merocel (gloved) and strip gauze were the most common nonabsorbable packing materials, but not as common as absorbable packing materials. Of note, a significant minority of experts never use nondissolvable (17.5%) or dissolvable packing (26.7%). In line with this, a minority of experts do not use packing, Asmaro et al. [175] followed 73 consecutive patients who underwent endoscopic repairs of various skull base defect etiologies and sizes, and reported a 97.3% success rate despite no sinonasal packing being used. This may suggest the interplay of technical factors and other adjunctive measures (e.g., tissue sealant, LD) in ensuring reconstructive success.

The ICSB and other summative works note that nasal packing outcomes research is scarce and practices are likely based on surgeon preference, although a growing body of literature suggests nasal packing tends to be safe and has no long‐term impact on sinonasal outcomes [5, 90, 176], despite causing short‐term detriments to quality‐of‐life [177]. The ARS EPS (Part 1) assessed the literature and found that the safety profile of both absorbable and nonabsorbable packing is favorable, and that packing may be an option for bolstering the repair, especially following extended approaches [24]. Gelatin sponge is often utilized as a “peel‐away” layer to provide a bolster between removable packing and the underlying onlay layer so that the reconstruction does not get displaced when packing is removed. This is consistent with several experts specifically mentioning absorbable packing use with for high‐flow leaks and when a FMG or pedicled intranasal flap is utilized. Oxidized cellulose is increasing in popularity for placement around edges of the onlay to anchor placement while allowing for palpation of underlying bone edges, though it has also been shown to be associated with mucosal breakdown in vitro [178]. Some experts may use oxidized cellulose as a standalone repair for sellar defects with minimal to no CSF leak [52]. Dissolvable packing may also afford a lower postoperative infection rate and a similar postoperative CSF leak rate and quality of life compared with nondissolvable packing regardless of extent of surgery, CSF leak flow, or vascularized flap use [176]. Of note, while a few experts mentioned specific defect locations, sizes, or other characteristics that informed their decision to use packing, no discernable patterns could be elucidated about dissolvable or nondissolvable packing use.

The popularity of Merocel packs may be due to its ability to apply directed pressure to the repair, ease of placement and removal, and permitting nasal breathing, although there is risk of displacement if too small. The relatively uncommon use of the Foley balloon suggests that it may be falling out of favor, possibly due to risk of displacement and the inability to apply directed pressure or receive tactile feedback from placement over the repair site. A recent meta‐analysis also demonstrated the improved efficacy of nondissolvable nasal packing over balloon use for preventing postoperative CSF leaks after low‐flow CSF leak reconstruction [89]. Emerging studies should aim to better understand exact indications for different packing types as well as technical factors related to packing placement and location that may impact quality of life and postoperative infection and CSF leak.

4.12. Lumbar Drain

The use of peri‐ and postoperative LD for ESBS remains controversial to date, even in light of strong evidence to support its routine use for large defects of the ACF and PCF [8, 179, 180, 181]. Overall, 7.5% of experts never used LD in the postoperative setting. Common reasons for experts to use an LD included for PCF defects (most common), high‐flow leaks, SS defects, and risk factors for postoperative leak, that is, prior irradiation and confirmed or suspected high ICP. Overall, the incidence of LD use for the highest risk patients remains low (<50%), however, suggesting some inconsistencies in responses. The recently published ARS EPS (Part 1) endorsed surgeons to consider LD use for “large ACF or PCF skull base defects, or in patients with risk factors for postoperative CSF leak.” [24] These trends are consistent with those reported in the literature [8, 182, 183]. Among experts who used LD, the most common duration was approximately 2–3 days while 30% of experts use an LD for more than 3 days. This may be due to a perceived a lack of benefit beyond this time frame with increased risk of adverse events and/or length of stay [184, 185, 186]. The most commonly reported drainage rate was 5–10 mL/h.

Overall, the lack of consensus and divergent LD practices among experts in this study reflect the heterogeneity in outcomes reported in the literature. Several retrospective series, meta‐analyses, and systematic reviews have suggested that prophylactic LD use does not reduce the risk of postoperative CSF leak and may actually increase the risk of repair failure or meningitis [180]. Many of these studies, however, included spontaneous leaks and were prone to selection bias, as LD use was presumably more common when confidence in reconstruction was lower or there was a large dural defect with high‐flow leak [5]. More recent evidence in the form of a randomized controlled trial demonstrates the potential benefit of LD for high‐risk, surgically created skull base defects [62, 149]. Based on published evidence, surgeons should likely take pause before using an LD for all defects, as paralleled by most experts steering away from always using an LD. The recent high‐quality data support considering a LD in high‐risk scenarios and for large dural defects, particularly of the ACF and PCF, which is also in line with the practices of most experts. Future studies should aim to understand the “balance” between minimizing LD duration and drainage rates to minimize LD complications while preserving reconstructive success.

4.13. Approaches and Methods for Repair of Frontal Sinus Posterior Table Defects

Frontal sinus posterior table defects commonly arise from trauma, but can also be spontaneous due to IIH, congenital, iatrogenic during rhinologic or neurosurgical procedures, or secondary to oncologic resection. For many traumatic cases that fail conservative management with bedrest, head‐of‐bed elevation, and LD, surgical repair is necessary to prevent mucocele formation, pneumocephalus, meningitis, and persistent CSF leak. Frontal sinus defects can be a point of divergence from other anterior skull base defects due to their anatomically challenging nature. Approaches also vary depending on defect location, although endoscopic Draf 2a/2b/2c, Draf 3, and periorbital suspension techniques are now often preferred over or in combination with open approaches when possible [17, 187, 188]. This is due to improved high‐definition view, ability to preserve a functional and patent sinus, reduced morbidity with no external incisions, and reduced hospital stays [17, 179, 180, 189, 190, 191, 192, 193].

Table 6 summarizes common themes and the main points of divergence within the expert teams for frontal sinus posterior table reconstruction. In our study, all experts preferred an endoscopic approach for medial posterior table defects. For far lateral (i.e., lateral to the midpoint of the orbital axis) or superior defects, gaining access for appropriate graft positioning, fracture reduction, and encephalocele ablation can be challenging through a purely endoscopic approach and may require hybrid endoscopic‐open approaches such as frontal trephination, a transorbital (e.g., upper eyelid or brow) approach, or an osteoplastic flap. The design of angled endoscopic frontal instrumentation may present inherent limitations for accessing far lateral and superior defects; a cadaveric study demonstrated that successively wider Draf openings from 2a to 3 improved access and visualization and that the maximum lateral and superior reaches with instrumentation were 16.8 ± 5.4 and 29.4 ± 7.4 mm from the frontal ostium with a Draf III, respectively [194, 195]. Several studies now showcase the success and feasibility of purely endoscopic repair of far lateral and superior defects using a Draf 3 approach with or without periorbital suspension and LD placement [17, 187, 189, 191, 192, 194, 196, 197, 198, 199]. Notably, Jones et al. [191] demonstrated successful endoscopic repair of a defect 3 cm above the base of the posterior table, indicating that the limits of endoscopic access are gradually being surmounted.

In the present study, many experts consider a purely endoscopic approach for lateral defects with a significant number also considering combined open‐endoscopic approaches. Direct brow or transorbital approaches (32.5%) were slightly favored over frontal trephination (27.5%) and osteoplastic flaps (22.5%). While all open approaches provide excellent exposure to the lateral and superior frontal sinuses, the osteoplastic flap approach was likely least common given it requires a coronal incision with a large osteotomy encompassing the entire anterior table. This is in contrast to a much smaller incision hidden in the eyebrow for frontal trephination and a superior palpebral crease incision with an upper eyelid approach [120, 190, 200, 201, 202, 203, 204, 205, 206, 207, 208]. Both trephination and superior eyelid approaches also require a much smaller osteotomy and can be combined with endoscopy for improved visualization [120, 190, 206, 207, 209]. The only meta‐analysis to date comparing open and endoscopic approaches for posterior table fractures showed a higher mucocele rate in patients undergoing open repair and no difference in postoperative CSF leak or meningitis rates; however, there were significant limitations, including a selection bias for larger and more complex fractures in open repair studies and the scarcity of prospective outcomes data on endoscopic repair techniques [210]. Thus, the study concluded that no strong recommendation could be made regarding the superiority of either option and that the approach should be based on surgeon experience, preference, and the complexity and location of the defect. Ultimately, both open and endoscopic approaches should be considered in the decision‐making process regarding posterior table defect management, and the anatomical constraints of the frontal sinus should be taken into consideration alongside optimizing mucosal preservation, outflow tract patency, and defect access and identification while minimizing morbidity.

In terms of reconstruction technique, most expert teams favor a single inlay (70.6%) and onlay layer (97.1%). Common inlay materials among experts were collagen matrix, fat, FL, and ECM‐based scaffolds, which may be influenced by defect size, surgeon preference, and the lack of literature or consensus on optimal graft material [189, 190, 195]. FMGs and NSFs were the most popular onlays with a similar reported frequency (Figure 8). It is perhaps surprising that more experts consider a NSF (64.7%) for posterior table defects than spontaneous and traumatic ethmoid roof/cribriform plate leaks given it is more difficult for NSFs to reach the posterior table, though most posterior table defects tend to be medial and inferior. Generally, NSFs can extend up to 3 cm along the posterior table although certain techniques like the sphenoidal slit relaxing incision can further extend its reach [211, 212]. Posterior table defects are often traumatic and may be larger than ethmoid defects with an average posterior table bony defect size of 17 mm in maximum dimension [189, 191]. Surgeons may prefer more robust vascularized tissue to overcome a perceived higher postoperative CSF leak risk afforded by the more technically challenging nature of working in the frontal sinus with angled instrumentation and scopes. A hemitransfixion incision can maximize NSF length and placement along the medial orbital wall can improve pedicle rotation for lateral defects [191]. No dedicated study to date has compared FMGs with NSFs for frontal defects, although it is suspected they are likely equally efficacious given these defects are associated with low‐flow CSF leaks.

4.14. Traumatic and Iatrogenic Cribriform/Ethmoid CSF Leak

A large majority of traumatic ethmoid CSF leaks tend to close spontaneously after a period of observation and implementation of conservative measures such as bedrest, head of bed elevation, and, traditionally, CSF diversion (i.e., LD). After a period of failed observation not exceeding 7–10 days, endoscopic repair can lead to successful closure of the defect and decreased morbidity [213, 214]. However, when there is active CSF leakage, some experts prefer immediate repair of traumatic defects because while mucosal violations may heal, there is concern that the dural defect may not close with continued risk of meningitis [170]. Endoscopic repair of these defects is typically less complex than reconstruction for large skull base defects for tumor surgery. Iatrogenic leaks, on the other hand, are created inadvertently during sinonasal surgery, and should be recognized and repaired as soon as possible. In our study, experts had a very similar approach to both defects with an inlay layer whenever possible, but more importantly an onlay layer. Although almost half the experts do not use any inlay for traumatic CSF leak repair, subdural placement of collagen matrix or fat is preferred by the majority of the experts who do place an inlay. For iatrogenic cribriform/ethmoid defects, about a third of experts preferred no inlay layer; the majority of experts who do use an inlay prefer either subdural or epidural placement of synthetic material, fat, or FL. For onlay repair of iatrogenic and de novo traumatic cribriform/ethmoid leaks, the vast majority of experts preferred a FMG. Table 6 summarizes common themes and the main points of divergence between expert teams for iatrogenic and traumatic ethmoid/cribriform defects.

While half the experts did not prefer the use of an inlay graft for traumatic CSF leaks and a third did not prefer the use of an inlay graft for iatrogenic CSF leaks, the majority preferred at least one onlay graft layer. The rationale behind the use of solely an onlay graft may be due to the physiology of a freshly made traumatic defect. The use of a FMG, as the vast majority of our respondents prefer, promotes healing through providing a proper patch over the defect. Previous literature describes a similar approach to management, with multilayer reconstruction for larger traumatic CSF leaks and single‐layer reconstruction for smaller traumatic CSF leaks [214, 215].

4.15. Spontaneous Ethmoid and Lateral Recess CSF Leak/Meningoencephalocele

A growing body of literature now supports the theory that most spontaneous CSF leaks and encephaloceles occur in the setting of IIH. While rare overall, the most common risk factors are obesity, middle age, and female gender, which are increasingly relevant as the obesity epidemic is worsening internationally [216, 217, 218, 219, 220, 221]. Common areas for spontaneous CSF leaks include the ethmoid roof/cribriform plate, SSLR, and posterior table of the frontal sinus [138, 217, 222]. While these areas do not directly communicate with a subarachnoid cistern or ventricle, patients commonly have elevated ICP with lumbar puncture opening pressures >30 mm Hg either prerepair or shortly after endoscopic repair, likely due to sealing of the defect and reestablishment of a closed‐pressure system [139, 140, 216, 217, 219, 220, 223].

Surgical management is crucial to repair the defect and reduce the risks of life‐threatening neurologic sequelae. Yet, spontaneous CSF leak repairs have a higher failure rate than congenital, traumatic, and iatrogenic CSF leaks given the higher prevalence of encephaloceles, the increased frequency of multiple simultaneous skull base defects, and underlying IIH [138–140, 222, 224]. To increase the likelihood of surgical success and prevent future spontaneous skull base defects, postoperative ICP management with carbonic anhydrase inhibitor diuretics like acetazolamide, permanent CSF diversion (i.e., shunting), and/or dural venous sinus stenting in patients with dural venous sinus stenosis may also be crucial [5, 139, 143, 221, 225, 226, 227, 228, 229, 230, 231, 232, 233, 234]. The endoscopic endonasal approach to spontaneous CSF leak repair is now considered standard of care amongst otolaryngologists and neurosurgeons when appropriate, with lower morbidity and postoperative CSF leak rates that rival or are superior to repair via an external approach [109, 138, 221, 223, 227].

In terms of ethmoid/cribriform CSF leak and meningoencephalocele reconstruction in this study, experts are divergent on placement of an inlay graft with 41.2% preferring no inlay and 58.8% preferring a single inlay (Figure 9). Subdural inlays were more common with collagen matrix, ECM‐based scaffolds, fat, and FL being the most common materials. Very few experts specifically mentioned rigid reconstruction with bone or cartilage as an inlay. For spontaneous SSLR leaks (Figure 10), experts were more likely to place an inlay with 55.9% preferring one layer and 23.5% preferring two or more layers. Materials similar to traumatic ethmoid/cribriform defects were used with subdural placement being slightly preferred. Rigid reconstruction and “gasket seal” technique was also more common (23.5%) in this location. Table 6 summarizes common themes and the main points of divergence between expert teams for spontaneous ethmoid and SSLR defect reconstruction. Inlay placement and rigid reconstruction for spontaneous ethmoid/cribriform defects were likely less common than for SSLR defects given it is often very difficult to undermine dura and create an epidural pocket for graft placement due to olfactory fila descending through the cribriform plate and the crista galli medially [109, 221]. A fifth of experts also do not use inlays for SSLR defects, possibly due to the generally small size of these defects.¹⁰⁸ When dural undermining is difficult but there is a visible dural defect, a small subdural “plug” of FL, fat, or synthetic tissues like acellular dermal matrix or collagen matrix may be used. A plethora of retrospective and a few prospective cohort studies have demonstrated the high success rates of repair with various inlay grafts and repair methods, although none have compared different graft materials and their impact on long‐term repair integrity [5, 138, 139, 193, 217, 218, 221, 223, 224, 227, 235, 236, 237].

The choice of graft and number of layers likely heavily depends on access to the defect, location, size, and suspected or diagnosed IIH, which is difficult to control for when comparing various grafts. Ultimately, placement of a subdural graft and choice of material is likely influenced by surgeon preference and experience and available materials given a variety of methods have a high success rate. When dural undermining is possible, a rigid bone or cartilage graft may be used, although a minority of experts currently prefer this technique. This may be due to the fact that the surrounding bone is also thin from chronic underlying IIH and may fracture very easily [140]. Several studies have demonstrated the feasibility and high success rates with epidural bone/cartilage grafts and gasket seal reconstruction for spontaneous CSF leaks [109, 139, 140, 217, 220, 222, 227, 235, 238–240]. These epidural bone/cartilage grafts also tend to integrate well into the skull base on long‐term follow‐up.

In terms of onlay reconstruction, experts predominantly prefer a single onlay for both ethmoid/cribriform and SSLR defects. Interestingly, FMGs were slightly preferred over NSF (64.7 vs. 50%) for ethmoid defects and NSFs slightly preferred over FMGs (64.7 vs. 50%) for SSLR defects (Figures 10 and 11 and Table 6). For SSLR leaks, experts endorsed various approaches to the SSLR and both ipsilateral or contralateral NSF harvest depending on the approach [239, 241]. Most experts use a contralateral NSF that crosses over via a posterior septectomy. Some experts use an ipsilateral NSF likely due to familiarity and experience with ipsilateral sphenopalatine artery preservation techniques [242]. The higher rate of NSF use for SSLR defects may be due to a possible higher risk of postoperative CSF leaks in this area and a lower confidence in the reconstruction in certain cases that have technically challenging approaches for exposure relative to ethmoid roof defects [109]. Many experts may also prefer a NSF over a FMG based on a specific size of the dural defect or when multiple simultaneous separate defects are suspected and wide area of coverage is required, especially along the ethmoid roof [138, 140, 217, 218, 220, 221, 224, 235, 240].

Several studies argue that multilayered repair of skull base defects, when possible, in the setting of IIH may be more efficacious or preferred than a single onlay reconstruction. Additionally, many of these studies have shown no difference in CSF leak recurrence between FMGs and NSFs for spontaneous cribriform/ethmoid or SSLR CSF leaks with or without encephaloceles [5, 109, 139, 193, 218, 221, 222, 223, 227, 235, 236, 237, 239, 240, 243, 244]. Per the ICSB, the literature on different reconstruction methods for spontaneous CSF rhinorrhea is overall poor and predominantly based on expert opinion and small retrospective series; the current recommendations are to base the repair on surgeon preference with consideration of defect size and location and measured ICP [5]. The expert opinions in this study largely reflect the heterogeneity of thought and practice amongst skull base surgeons and the lack of strong evidence supporting a specific reconstruction method for spontaneous skull base defects as emphasized in the ICSB and the high overall success rates with repair. It is perhaps possible that recognition and strict postoperative management of IIH is more crucial than the choice of onlay given these defects almost always have a small dural opening [37].

4.16. Postoperative Care Protocol

Postoperative management after SBR frequently varies among surgeons, with no discrete consensus [245]. A recent systematic review highlighted the need for more robust literature to establish optimal postoperative protocols after ESBS [8]. In this study, we were able to identify common themes, points of divergence, and trends in postoperative management protocols (Tables 7 and 8) that are complementary to the findings in a recent cross‐sectional survey study of the ARS, NASBS, and AHNS membership regarding postoperative management [245]. One key debate is regarding the timing of mobilization (i.e., duration of bedrest) after ESBS to balance the risk of ICP shifts impacting the fresh repair with the associated morbidity of venous thromboembolism (VTE) although short‐term bedrest likely does not increase the risk of VTE [246]. A recent large retrospective analysis also showed that risk of VTE after ESBS is low (∼2.3%), but certain comorbidities (such as malignancy, preexisting endocrinopathies, obesity) or Caprini score >5 can lead to increased risk of VTE [185, 247, 248]. The rationale behind bedrest after ESBS is to decrease sudden shifts in ICP to prevent failure of repair. This justification stems from the literature on traumatic CSF leak management [249]. Although literature surrounding duration of bedrest is lacking, some studies do show that prolonged bedrest (>24 h) after ESBS is not necessary [166, 250, 251]. In our study, the majority of expert teams preferred <24 h of postoperative bedrest (60%), while another sizable proportion (25%) preferred 24–72 h of bedrest. Interestingly, bedrest restrictions were more lenient among US experts in our study compared with non‐US experts, which may relate to inpatient/hospital constraints unique to the US healthcare system, a larger focus on VTE prevention in the US healthcare system, and an effort to decrease ICP with early ambulation especially in the absence of an LD. A recent survey‐based study showed 83–85% of European endoscopic skull base surgeons recommend bedrest, often for at least 48 h for extended ACF, transplanum, and PCF approaches [14]. Of note, urinary catheters are often utilized while patients are on bedrest; the rate of urinary tract infections after ESBS has been reported to be quite low (1.3%) and associated with advanced age, longer catheter duration, longer hospital stay, and premorbid genitourinary conditions [252].

Furthermore, postoperative straining may play an important role in developing diaphragmatic tears and a delayed CSF leak after sellar surgeries in which no intraoperative leak was identified [77]. A recent retrospective series demonstrated that constipation is highly prevalent after ESBS (69%) and is associated with longer bedrest and higher morphine dosing, but may not increase the rate of postoperative CSF leak [253]. Extra consideration can be allotted to ESBS patients at higher risk of postoperative nausea and vomiting, which includes female sex, cavernous sinus dissection, and extended surgical approach [254].

In contrast to the divergent views on bedrest, nasal precautions and activity restrictions to prevent rapid ICP shifts (i.e., limiting Valsalva through limiting straining, heavy lifting, strenuous activities, and nose blowing; sneezing and coughing with mouth open; head elevation, and use of stool softeners) are an important part of postoperative protocols among all experts [255, 256, 257]. However, most expert teams do not place restrictions on usage of straws by patients postoperatively, which is in line with results from a recent study on straw usage after ESBS [258]. Activity restrictions were around 4 weeks for the majority of the expert teams, which is similar to the 3–6 week activity restriction published by the ARS EPS (Part 2) [259]. This suggests experts are generally conservative with postoperative precautions and possibly aim to prioritize skull base healing over the nuisance of activity restrictions. There remains no consensus into this area and further research efforts into elucidating appropriate timing of lifting restrictions may benefit patient quality of life.

OSA is a significant and common comorbidity in adult patients, with CPAP being the gold standard for long‐term treatment [260]. OSA can be underdiagnosed in patient with skull base pathology, which can lead to increased risk of respiratory complications and CSF leak [261]. A large retrospective analysis of national inpatient data of transsphenoidal pituitary surgeries showed that OSA was associated with increased risk of pulmonary and airway complications, but not CSF leak [262]. Earlier initiation of CPAP after ESBS leads to the theoretical concern for compromise of the repair site with subsequent CSF leak and/or tension pneumocephalus. Additionally, patients with OSA undergoing ESBS may develop CSF leak earlier than patients without OSA, which is thought to be related to underlying elevated ICP [263]. However, a recent study reported similar rates of CSF leak/tension pneumocephalus in patients with OSA with or without application of CPAP immediately following endoscopic pituitary surgery [264]. Another retrospective study in OSA patients undergoing transsphenoidal surgery showed no increased risk of tension pneumocephalus with early resumption of CPAP [265]. A recent systematic review also concluded that resumption of CPAP after endoscopic pituitary surgery appears to be safe [266]. Nevertheless, practice patterns regarding initiation of CPAP after ESBS among skull base surgeons vary [9, 11, 12]. Preoperative screening for OSA is often underperformed and a documented postoperative plan for management of OSA is often lacking after ESBS [265, 267].

Fortunately, there has been recent interest in developing protocols for resumption of CPAP after ESBS. Gravbrot et al. [268] reported no increased risk of CSF leak or pneumocephalus after resumption of CPAP on average 3.5 weeks after transsphenoidal surgery with proposed CPAP management algorithm in OSA patients. Cadaveric studies have shown that 85% of CPAP pressure is delivered to the nasal cavity depending on settings [258], while ∼80–84% of CPAP pressure can reach the sphenoid sinus [269]. A follow up quantitative study among healthy individuals validated these results with a reported average of 85% of CPAP pressure reaching the nasal cavity, with higher pressures delivering a greater percentage of pressurized air to the nasal floor [258]. Another cadaveric study by the same group showed that a NSF onlay appears to be able to withstand up to 20 cm H₂O CPAP pressure [270]. Last, a recent editorial by Rabinowitz et al. [259] highlighted their practice protocol following sellar surgery with the decision to resume CPAP through a patient‐centered approach with specific attention to OSA severity, intraoperative findings, and method of SBR, with recommendation to restart at the lowest possible pressure setting. Extrapolating from the findings from Chitguppi et al., it may be safe to resume CPAP earlier in patients with a NSF onlay, though this should be individualized [270]. CPAP resumption after more extended skull base approaches is yet to be determined due to a lack of dedicated studies. In our study, CPAP restrictions after ESBS between 2 and 4 weeks were implemented in most experts’ postoperative protocols, which is similar to the at least 2–6 week duration reported in the ARS EPS (Part 2) and generally follows the immediate postoperative healing period where CSF leaks are unlikely to occur [259].

The literature regarding safety of air travel resumption after ESBS is scarce. It has been anecdotally noted that commercial air travel utilizes safe cabin pressures that would be unlikely to affect skull base repairs since regulatory governmental agencies require cabin altitude to not exceed 2438 m [271]. However, since the gas in body cavities can expand at low cabin pressures, the Aerospace Medical Association Medical Guidelines Task Force has recommended that neurosurgical patients wait at least 7 days before air travel [272]. Furthermore, individuals with active CSF leaks are recommended to avoid air travel until the leak is repaired due to the possibility of backflow and microbial contamination caused by cabin pressure changes. In our study, the majority of the experts cleared patients for air travel 2–4 weeks postoperatively. This is congruent with the 2–4 weeks waiting period recommended in the ARS EPS (Part 2) [259]. Additionally, there was no consensus on usage, duration, or type of perioperative and postoperative antibiotics, as previously suggested by Saleh et al. [273]. This is consistent with previous literature although again lacking consensus on antibiotic coverage and duration [5, 14, 247, 273].

For timing of endonasal debridement, expert protocols were heterogeneous, with the majority of them performing some form of nasal debridement away from the skull base (including nonabsorbable packing removal) around 2 weeks. Similarly, the timing of saline irrigations varied widely among experts but tended to correlate with timing of debridement. The ARS EPS on postoperative precautions (Part 2) reached a consensus that saline sprays are usually initiated within 72 h, irrigations may be started after the concern for immediate postoperative leak is low (median 14 days), and that debridements can be performed safely without compromising the reconstruction, although the extent of debridement, that is, anterior nasal cavity versus up against the reconstruction, varies [259].

4.17. Limitations

Several limitations should be considered when interpreting the results of this study as a whole. This work is qualitative in nature and the focus is upon delineating themes and central concepts, and thus does not rely on quantitative methodology (e.g., inferential statistics) for results reporting. During structured interviews, experts were asked to assume the largest dural defect possible, and thus the reported reconstruction techniques and materials may not represent experts’ views on repair of smaller defects in the same location, though we conservatively solicited this condition in order to ascertain key principles. Although the algorithms presented here represent the most common scenarios encounter for specific etiologies of skull base defects and CSF leaks, ultimately the defect, including location, size, and observed flow rate, should dictate how the repair is performed and any relevant postoperative precautions. For instance, a large traumatic defect of the planum sphenoidale would likely require repair following the principles of a SS posttumor resection defect. For certain techniques that were used by the minority of experts (e.g., rigid reconstruction), data gathering was not performed to the same level of granularity (e.g., specific type of rigid reconstructive material) as more commonly used techniques. We did not provide detailed information regarding long‐term ICP management in spontaneous CSF leaks and encephaloceles as much of these practices has been covered in similar capacity by Georgalas et al. [274]. Experts’ outcomes were also not assessed (i.e., postoperative CSF leak rates), and thus, conclusions cannot be drawn about the most optimal method(s) of reconstruction, though certainly the extensive experiences of the group provided invaluable themes and guiding principles. The steering committee's primary goal was to report on the current state of SBR by experts given the significant heterogeneity in outcomes and methods in published literature and lack of high‐level evidence on SBR, especially for inlay repair. Additionally, there is no standardized or uniform nomenclature for specific repair techniques and layers of reconstruction, and thus, reporting and interpretation biases exist. Despite our structured interview format, qualitative interviews have inherent limitations and experts may have inadvertently omitted certain aspects of their repair techniques, postoperative care, or preferred materials. Differences in surgical techniques may have led to slight overrepresentation of vascularized flap usage, as some surgeons may utilize a rescue flap approach while others routinely raise a NSF upfront regardless of the eventual dural defect size; however, we combat this limitation and standardize results as optimally as possible by asking interviewers to assume the largest defect size possible. Additionally, a survey sampling bias also applies given only experts, as defined in the Methods, were interviewed. Needless to say, despite representing the opinions and experiences of experts, the study by no means can exhaustively capture all the outstanding techniques and experiences used across the world, and certainly is not meant to be interpreted as guidelines or standard of care—these guiding principles and techniques should be tailored toward patient factors and surgical team preferences.

4.18. Knowledge Gaps and Opportunities for Future Research

Despite progress and growing interest in this area, there remains significant knowledge gaps and opportunities for improvement, as well as numerous pending research directions. These include, but are not limited to:

Fundamental Principles

• How CSF fluid dynamics impact technical and postoperative considerations for SBR

• How defect size, shape, and volume contribute to challenges in SBR

• Natural history, timing, and progression of wound healing of the skull base with various graft types, and how prior surgery and/or radiation and/or chemotherapy affect this

• Biomechanical properties of graft placement within and over skull base defects

• Optimal algorithms for diagnosis of both untreated and postoperative CSF leaks

• Biological basis of managing postirradiated surgical fields that make reconstruction challenging

Technical Factors

• Improvement in the quality of evidence for the effects of interventions, in the form of randomized controlled trials

• Understanding the individual contributions of subdural and epidural inlay placement

• Nuances in graft and flap contouring and placement, which optimize wound healing

• More effective means of creating watertight seals

Postoperative Management

• How ICP shifts impact fresh repairs

• How much force or pressure is generated by a given postoperative maneuver (e.g., coughing, straining)

• Optimal postoperative protocols that balance patient conditioning, quality of life, and reconstructive outcomes

5. Conclusion

With multi‐institutional and international representation, the present mixed‐methods data exemplify the current state of reconstruction and management of endoscopic skull base defects as endorsed by interviewed experts. Common themes and discrepancies are noted, with commonalities being core guiding principles that may represent the distillation of accrued experience and expertise, while discrepancies are important to understand in order to target research and education endeavors (Table 6). Though the current study does not serve as guidelines, we hope that the content will provide a starting point or a compendium to reinforce key concepts for all skull base teams.

Conflicts of Interest

The authors declare no conflicts of interest.

Financial Disclosures

ECK is a consultant for Stryker and 3‐D Matrix and receives royalties from Springer. JRC is a consultant for Aerin Medical. KMP has equity in SoundHealth and is on the advisory board for Sanofi. NDA and JNP are consultants for 3‐D Matrix, Acclarent, and Optinose. AMS is on the advisory board for Sanofi. PSB is on the advisory board for Neurent Medical. JJE is a consultant for Mizuho. MF is on the advisory board for Medtronic. PAG is a consultant for Mizuho, Peter Lazic US, SPIWay, Stryker, and Sutter Medizintechnik GMBH. CG is a consultant for Medtronic, Olympus, and GlaxoSmithKline. ELM is a consultant for Stryker. PN is on the advisory board for Medtronic. ZMP is a consultant for Medtronic, Dianosic, Optinose, Wyndly, and Mediflix, and has equity in SoundHealth and Olfera Therapeutics. MRR is a consultant for Medtronic and Integra. CHS is consultant for and has equity in SPIWay, and is a founder of (with equity in) Respair. None of the above disclosures are relevant to this work. The remaining authors declare no relevant disclosures.

Supporting information

Supporting Information

Kuan E. C., Talati V., Patel J. A., et al. “Expert Strategies: Skull Base Reconstruction—Global Perspectives, Insights, and Algorithms through a Mixed Methods Approach.” International Forum of Allergy & Rhinology 15, no. 10 (2025): 1032–1069. 10.1002/alr.23596