Improving Surgical Outcomes in Middle Cranial Fossa Cerebrospinal Fluid Leak Repair

Abstract

BACKGROUND:

Spontaneous cerebrospinal fluid (CSF) leaks of the temporal bone occur in the absence of known iatrogenic or traumatic injury and without underlying congenital malformation. Holistic treatment of the condition requires meticulous perioperative evaluation of the patient to mitigate underlying risk factors. Similarly, surgery for CSF leaks requires careful consideration of all potential routes of CSF leakage to improve short- and long-term surgical outcomes.

OBJECTIVE:

To describe our surgical technique in this article, which addresses most of the potential routes of spontaneous CSF otorrhea. Perioperative management of the patients is also described.

METHODS:

A total of 65 patients underwent CSF leak repair using a middle cranial fossa approach and the techniques described in this paper. Their surgical outcomes are described.

RESULTS:

Preoperatively, all patients had either biochemically proven beta trace protein–positive CSF otorrhea or the presence of an encephalocele on preoperative imaging. Using this technique, all patients had short-term successful repair of their CSF leak, whereas a long-term success rate of 87.7% was achieved. No major complications were encountered.

CONCLUSION:

Holistic treatment of spontaneous CSF leaks of the temporal bone, together with using a surgical approach that considers all potential routes of CSF leakage, may help to improve long- and short-term surgical outcomes.

ABBREVIATIONS:

BTP

beta trace protein

EAC

external auditory canal

IGS

image-guided surgery

OSA

obstructive sleep apnea.

Spontaneous cerebrospinal fluid (CSF) leaks of the temporal bone occur in the absence of known iatrogenic or traumatic injury and without underlying congenital malformation. It is a problem that is increasingly encountered in our practice.^1,2 Holistic treatment of the condition requires meticulous perioperative evaluation of the patient to mitigate underlying risk factors such as obesity, obstructive sleep apnea (OSA), and other causes of raised intracranial pressure.^3-9 Similarly, surgery for CSF leaks requires careful consideration of all potential routes of CSF leakage to improve short- and long-term surgical outcomes.

We have demonstrated that defects in the temporal bone in patients with spontaneous CSF leaks are multifocal and vary in size. In our recent publication, radiological assessment of the skull base in patients with spontaneous CSF leakage revealed defects most commonly occurring in the anterior tegmen mastoideum accounting for more than 50% of cases, followed by the anterior tegmen tympani. Notably, almost two-thirds of patients had at least 3 defects identified within the tegmen at varying locations bilaterally, despite presenting with unilateral symptomatology, reflective of the multifocal nature of this disease.¹⁰ The size of these defects varied (1-10 mm) but a majority of patients had defects greater than 2.5 mm on both the affected and unaffected sides.¹⁰ In addition, although the bony defects have been characterized, the role of adjacent dura mater defects remains less certain.

This article describes the surgical technique we use to repair spontaneous CSF leaks of the temporal bone via a middle cranial fossa approach. This technique, which assumes that the sources of the leak into the middle ear originates from the overlying middle cranial fossa surface of the temporal bone and adjacent dura, aims to address the multifocal nature of potential routes of CSF leakage to achieve improved rates of surgical success. We also outline the routine perioperative evaluation of all patients with CSF leaks to diagnose and mitigate medical risk factors. Finally, our surgical outcomes are described.

METHODS

Preoperative Evaluation

All patients who present with possible CSF leaks of the temporal bone undergo aspiration of middle ear fluid for beta trace protein (BTP) for biochemical confirmation of the diagnosis. They then undergo high-resolution computed tomography (CT) temporal bone scan with additional cuts of the face (image-guided surgery protocol). All patients also undergo an MRI brain/temporal bone scan to exclude coexisting meningoencephaloceles, anatomical anomalies, and venous sinus obstruction. Other than for surgical planning, imaging is also able to highlight any radiological evidence of raised intracranial pressure, which may require further evaluation and treatment preoperatively. Where indicated, MR venogram will be performed to further visualize the patency of the cerebral veins and venous sinuses. Where there is clinical suspicion of raised intracranial pressure, a neurology referral would be made for consideration of medical treatment and potential lumbar puncture.

In addition, because of the high incidence of OSA in patients with CSF leaks,^3,5,6,8,9 all patients also undergo a polysomnography.

Surgical Technique

The procedure is performed under general anesthesia and routine translaryngeal intubation. Long-acting muscle relaxants and the use of muscle relaxant reversal agents are avoided to prevent interference with subsequent facial nerve monitoring. Instead, only a single dose of short-acting muscle relaxant is used at the start of anesthesia and allowed to wear off naturally. The patient is positioned supine with the head turned 60 to 90° away from the side of surgery. A unilateral shoulder roll is placed to facilitate this position and to avoid over-rotation of the patient's neck and potential compression of the contralateral internal jugular vein. Once ideal positioning is achieved, the patient's head is secured with Mayfields pins. CT navigation for image-guided surgery (IGS) is set up. Two-channel facial nerve neuromonitoring is set up. These are illustrated in Figure 1. An indwelling urinary catheter and invasive radial arterial line is inserted to facilitate diuresis and blood pressure monitoring during the procedure. Acetazolamide 0.5 g/kg, levetiracetam 500 mg, and cephazolin 1 g are given intravenously.

FIGURE 1.

Operative setup.

A linear supra-aural incision measuring approximately 6 to 9 cm with an endaural extension towards the external auditory meatus is used. No hair shaving is necessary for this incision as the patient's hair can be parted along the incision and secured with water soluble gel (Figure 2A). Local anesthesia with 1:100 000 lignocaine with adrenaline is infiltrated into the wound. The skin incision is made and skin flaps are raised to expose the temporalis fascia. A linear incision in line with the external auditory canal is made through temporalis fascia and muscle, down onto the bone and subperiosteal flaps are raised to expose the cranium.

FIGURE 2.

A, A linear supra-aural incision with endaural extension is used. B, Middle fossa craniotomy. C, Middle meningeal artery (bleeding, black arrow), V3 (white arrow), and bony defect with adjacent thinned bone (black arrowheads). D, Middle meningeal artery (black arrow), Greater superficial petrosal nerve (asterisk) seen coursing anteromedially, arcuate eminence (white arrow), and bony defect (black arrowheads).

The position of the craniotomy is marked with guidance from CT navigation by determining the location of the middle cranial fossa and is centered along the vertical line of original incision. The middle fossa craniotomy is then performed with a craniotome and the size of the craniotomy varies between 4 and 5 cm in the horizontal and vertical planes but can be increased in size depending upon the access required (Figure 2B). The bony badge is carefully elevated off its underlying dura, taking care to keep it intact when removed and is preplated. Any residual bony ledges (especially inferiorly) is then taken down with a diamond burr to ensure full visualization of the floor of the middle cranial fossa.

Dura is then carefully elevated over the floor of the middle cranial fossa in a posterior to anterior direction, to avoid avulsion of the greater superficial petrosal nerve (GSPN) from the geniculate ganglion. A middle cranial fossa retractor is usually not required. Adequate elevation is crucial as there are often multiple bony defects in the skull base and other areas where the skull base is extremely thin. Failure to address all of these areas in the subsequent surgical steps can result in higher rates of recurrence postoperatively. Care is taken to keep the dura intact. The posterior limit of dural elevation is the superior petrosal sinus, while the anterior limit is the middle meningeal artery. If necessary for exposure, further anteromedial dissection can be undertaken with exposure of the mandibular branch of the trigeminal nerve (Figure 2C). The GSPN and the arcuate eminence are identified and confirmed with the assistance of IGS and facial nerve stimulation. Medially, elevation is carried past the tegmen tympani and over the arcuate eminence onto corticated bone (Figure 2D). As the landmarks on the middle fossa floor can be subtle, CT navigation is used to ensure that adequate dural elevation has been achieved. Facial nerve stimulation is also used to confirm the position of the GSPN to avoid unnecessary traction and subsequent facial nerve neuropraxia.

DuraGen (Integra LifeSciences) pieces are fashioned into "noodles" by cutting it into strips measuring 2cm. These DuraGen "noodles" are then wedged into the medial limit of the repair to assist in dural elevations (Figure 3A). The subsequent surgical steps use a 2-surgeon, 4-hands approach. A piece of DuraGen is cut and used to lay over the entire area of exposed dura, including the surface under the craniotomy (Figure 3B). The surgical assistant then uses a flat instrument, eg, Freer elevator to hold up the dura and DuraGen so that the bony middle cranial fossa floor remains exposed. Hydroset (Stryker) hydroxyapatite bone cement is then prepared by the scrub nurse and handed to the surgical assistant. The surgical assistant injects the hydroset bone cement over the middle cranial fossa floor. Simultaneously, the surgeon shapes the bone cement onto the middle fossa floor with a moist patty held on a bayonet forceps in one hand and a suction in the other hand to remove excess CSF and blood from the surgical field. Although the bone cement can set in the presence of CSF and blood, excess amounts can interfere with visualization and bone cement placement. This process is performed stepwise medially to laterally, until full coverage of the middle fossa floor is achieved (Figure 3C and 3D). Before the surgical assistant carefully releases his dural retraction by sliding the Freer elevator out, the bone cement is allowed to partially harden to the consistency of a soft putty. This prevents shifting of the repair. The above surgical steps are illustrated in this article's accompanying Video supplement.

FIGURE 3.

A, DuraGen noodles placed medially. B, DuraGen sheet placed over entire exposed dural surface. C, Bone cement injected stepwise medially to laterally. D, Bone cement covering entire middle fossa floor.

The bony badge is then replated. Gaps in the craniotomy are filled with bone cement. Closure of the wound is performed in layers. The Mayfield's pins are released and a mastoid bandage is applied for compression for at least 24 to 48 hours.

Postoperatively, the patient is kept on levetiracetam 500 mg twice daily for 1 week and augmentin 1 g twice daily for 5 days. The mastoid bandage is removed after 48 hours and the patient may be planned for discharge after.

Data Collection

All patients who underwent middle cranial fossa repair of spontaneous CSF leak of the temporal bone between January 2016 and January 2022 at 2 tertiary institutions were included in this study. Data collection was performed via retrospective chart review. Ethics approval for this study was granted by the institutional ethics review committee. Waiver of consent was granted by NHMRC National Statement on Ethical Conduct in Human Research [2007].

RESULTS

Intraoperatively, we found that the large majority of our patients had a thinned tegmen with multiple tegmen dehiscences. This is described in greater detail in a prior paper which studied clinical features and management outcomes in a similar cohort of patients (n = 38) with spontaneous CSF leaks across institutions in the state, where 73.7% of patients were found to have multiple tegmen defects.² In addition, a significant proportion of patients had CSF leakage from both dural defects and arachnoid granulations that extend into the inner table of the skull. To address these issues, we used the above technique, which ensures reconstruction of both the entire dural surface and middle fossa floor.

A total of 65 patients underwent middle cranial fossa CSF leak repair using the above technique between January 2016 and January 2022. The median age of the patients was 65 years. 50.8% of patients were female and 49.2% of patients were male. There were slightly more right-sided repairs (55.4%) than left-sided repairs (44.6%). Preoperatively, 90.8% of patients had biochemically proven BTP-positive CSF otorrhea and the remaining 9.2% had encephaloceles on MRI imaging. This is summarized in Table.

TABLE.

Middle Cranial Fossa CSF Leak Repair

n = 65
Median age	65 y
Sex
Male	32 (49.2%)
Female	33 (50.8%)
Side of CSF leak
Right	36 (55.4%)
Left	29 (44.6%)
Surgical indication
BTP-positive CSF leak	59 (90.8%)
Encephalocele on MRI	6 (9.2%)
Successful repair
Yes	57 (87.7%)
No	8 (12.3%)

BTP, beta trace protein; CSF, cerebrospinal fluid.

No immediate failure of the repair was noted. However, delayed failure of the repair was noted in 8 patients (12.3%). The median time to failure was 14 months. There were no major postoperative complications. Minor complications included temporary facial nerve palsy that spontaneously recovered (n = 1) and temporary dysphasia secondary to temporal lobe edema (n = 1). Median length of follow-up was 13 months.

DISCUSSION

This article describes in detail the use of a multilayered technique to repair spontaneous CSF leaks of the temporal bone via a middle cranial fossa approach. We have favored the use of a middle cranial fossa approach over a transmastoid approach as a significant number of patients in this study had a thinned tegmen with multiple defects over the skull base.¹⁰ The middle fossa approach allows wide exposure of the entire tegmen for resurfacing to prevent future leaks from other sites. Alwani et al¹¹ cited a similar reason for favoring a middle cranial fossa approach as 53% of the patients in their study had multiple tegmen defects. Similarly, 52.7% of patients in the series by Kutz et al had multiple tegmen defects.¹²

There have been multiple other studies in the literature describing results from a middle cranial fossa approach for repair of CSF leaks of the temporal bone. However, the perioperative investigations, preoperative preparation, and surgical technique have not been previously described in detail. Most authors in the literature agree on the superiority of a multilayered repair technique, although the materials used vary widely. Savva et al¹³ found a successful CSF leak repair rate of 75.4% when a single layered repair was used and a success rate of 100% when a multilayered repair was used. Alwani et al¹¹ highlighted improved success rates when multilayered reconstruction was performed with hydroxyapatite bone cement than when multilayered reconstruction was used without hydroxyapatite bone cement. As such, the authors of this study elected to use a multilayered repair technique for middle cranial fossa CSF leak repair. Alongside meticulous wide exposure of the skull base, the use of a assistant (4-hand technique) to provide adequate dural retraction, and the placement of DuraGen medially in the surgical cavity to lift up the dura medially, complete resurfacing of the entire skull base is achieved. We believe that this may improve surgical success. However, beyond surgical technique, we highlight the importance of preoperative screening for raised ICP and OSA, to allow holistic management of the condition both surgically and medically.

This is one of the larger studies in the literature describing a series of patients who have undergone middle cranial fossa repair of spontaneous CSF leak of the temporal bone. In our series of 65 patients, successful repair of CSF leak was achieved in 87.7% of patients. A meta-analysis by Gioacchini et al¹⁴ included results of 5 studies (n = 146) using the middle cranial fossa approach to repair CSF leaks and found an overall success rate of 94.1% (range 89.1-97.3). There is only a handful of other studies in the literature with a series of larger than 30 patients. A similar series (n = 65) by Nelson et al¹⁵ reported a success rate of 92.3%, although 23.1% of the patients had a lumbar drain placed perioperatively. Other studies on the subject with series of between 45 and 58 patients described success rates of between 90.9% and 97.3%.^11,12,16-18 Although the success rates of these studies are slightly higher than that described in this paper, direct comparison is challenging, given varying detail in reporting of patient characteristics, perioperative investigations, preoperative preparation, and surgical technique.

Limitations

The main limitations of this study would be its retrospective nature. Incomplete data points cannot be reported by this study. Although the majority of our patients had a follow-up duration of more than 1 year, it is possible that patients lost to follow-up had unrecorded complications or failures.

CONCLUSION

The aforementioned surgical technique can be used to address most of the potential routes of spontaneous CSF otorrhea. In our series, the procedure is safe, with a good long-term success rate. More studies are required to elicit the role of both meticulous surgical technique as well as control of medical risk factors in achieving long-term resolution of spontaneous CSF otorrhea.

VIDEO. Middle cranial fossa approach CSF leak repair.

Funding

This study did not receive any funding or financial support.

Disclosure

The authors have no personal, financial, or institutional interest in any of the drugs, materials, or devices described in this article.

COMMENTS

This is an interesting paper from an experienced Australian otological group on their techniques for repair of spontaneous CSF leaks via a middle fossa approach. This paper should be of interest to readers who are unfamiliar with the surgical management of spontaneous CSF leaks; however, the techniques reported here are not new. Hydroxyapatite bone cement was approved by the FDA for repair of CSF leaks in 1996.

The authors present a large retrospective series of 65 cases; in their hands, the procedure is safe, with a good long-term success rate of 87.7%.

The description of the surgical technique appropriately reports the use of contemporary technical adjuncts and their “how I do it” paper details how and why one executes the key maneuvers of the procedure.

The accompanying video nicely illustrates their technique.

Cormac G. Gavin

London, United Kingdom