Technical Considerations for Peripheral Nerve Sheath Tumor Excision With Intraoperative Neuromonitoring and Magnification

Abstract

Background:

Peripheral nerve sheath tumors (PNSTs) are benign tumors arising from Schwann cells within the peripheral nerve sheath that frequently present with pain but may also have accompanying focal neurological deficits. As there is limited literature describing techniques for PNST excision, this article aims to introduce our institution’s technique.

Methods:

A retrospective review of patients undergoing surgery for neurofibromatosis type 1, neurofibromatosis type 2, and schwannomatosis was conducted based on a single surgeon’s experience, including patients from 2009 to 2020. Chart review included patient demographics, clinical presentation, surgical details, pathology, and postoperative course.

Results:

A total of 78 operations were performed on 69 patients, excising 157 peripheral nerve tumors. The majority of patients were diagnosed with neurofibromatosis type 1 (41.0%), followed by neurofibromatosis type 2 (24.4%). Pain was the most common presenting symptom (82.1% of patients). Average follow-up was 5.56 ± 12.8 months. Lesions were most frequently located in the upper extremity (48.7%). The average number of tumors excised per case was 2.04 ± 1.59. Intraoperative nerve monitoring was used in 55.1% of cases, and nerve repair was required in 46.2% of cases. The overall surgical complication rate was 2.7%, and neurological complications accounted for 16.7% of cases.

Conclusions:

PNSTs present a difficult reconstructive challenge. By using intraoperative nerve monitoring, tourniquet control of the extremity, magnification, microsurgical instruments, enucleation from the tumor capsule where applicable, epineural repair, and fascicular repair when there is interfascicular resection, effective results can be achieved with low complication rates.

Takeaways

Question: How should peripheral nerve sheath tumors (PNSTs) be approached from a plastic surgeon’s perspective?

Findings: In a retrospective review of 78 operations on 69 patients (157 tumors) with PNSTs from 2009 to 2020, most patients presented with pain (82.1%), most commonly in the upper extremity (48.7%). Intraoperative nerve monitoring was used in 55.1% of cases, and nerve repair was required in 46.2%. The overall surgical complication rate was low at 2.7%, whereas neurological complications accounted for 16.7% of cases.

Meaning: Meticulous microsurgical technique with nerve monitoring enables effective PNST excision with low complication rates.

INTRODUCTION

Neurofibromatosis comprises a group of neurogenetic disorders involving the skin and nervous system that predispose patients to tumors of the nerve sheath.¹ These disorders include neurofibromatosis type 1 (NF1), neurofibromatosis type 2 (NF2), and schwannomatosis with incidences of 1 in 3000, 1 in 33,000, and 1 in 60,000 births, respectively.² All are dominantly inherited and display a high rate of de novo mutations and variable expressivity. The most common of the 3 syndromes is NF1. The major NF1-associated tumor is the neurofibroma; however, other clinical manifestations include bone dysplasia, learning disabilities, and increased risk of malignancy. NF2 is characterized by the presence of schwannomas of multiple cranial and spinal nerves, especially the vestibular nerve.¹ Finally, schwannomatosis is characterized by the presence of multiple noncutaneous peripheral nerve sheath tumors (PNSTs), with pain being the most prominent symptom.³ In contrast to these genetically associated tumors, some PNSTs can occur sporadically and are most commonly schwannomas.⁴

These PNSTs can be classified into benign, intermediate, or malignant types. Benign types include neurofibromas, schwannomas, and perineuriomas.⁵ Intermediate PNSTs, or atypical neurofibromatous neoplasms of uncertain biologic potential, represent lesions with at least 2 worrisome features such as nuclear atypia, loss of neurofibroma architecture, high cellularity, and/or mitotic activity greater than 1 per 50 but less than 3 per 10 high-power fields, but do not meet criteria for a malignant PNST.⁶ Malignant PNSTs are further classified into high-grade or low-grade tumors.⁶

Patients frequently present with pain. However, with increased tumor growth and nerve compression, this may lead to focal neurological deficits such as weakness, hearing loss, visual impairment, or chronic pain.^7,8

Treatment for PNSTs requires a multidisciplinary approach, the mainstay of which relies on surgical excision. If the tumor is asymptomatic or symptoms can be managed with multimodal pain control, patients can be observed with serial imaging.⁷ Benign tumors warrant excision when symptomatic and not controlled by medical pain control. Indications for surgery include pain, neurological deficits, significant tumor growth, or nondefinitive tissue diagnosis with biopsy alone.^5,7 In recent years, there has been significant progress in medical therapies for PNSTs. Specifically, for those with plexiform neurofibromas, the use of MAPK/extracellular-signal-regulated kinase (MEK) inhibitors such as selumetinib and mirdametinib can be used in pediatric and adult populations, respectively. These therapies are reserved for symptomatic, inoperable, and progressive tumors and are often associated with NF1.^9,10

Schwannomas (SWN) are well encapsulated and typically can be separated from the underlying nerve with intrafascicular dissection using magnification and microsurgical instruments, whereas neurofibromas may require nerve excision due to their tendency to intertwine with nerve fascicles.⁷ Currently, there are no evidence-based guidelines for the surgical management of these tumors. In NF2, management of PNSTs is complicated by frequent involvement of major peripheral nerves, sometimes involving multiple fascicles.¹¹ Despite this, it has been shown that PNSTs can be safely resected, even if they involve major peripheral nerves, using careful intracapsular techniques and neuromonitoring. As there is limited literature describing techniques for benign PNST excision, this article aims to introduce our institution’s technique, leveraging intraoperative neuromonitoring (IONM) in conjunction with visualization under magnification and the use of microsurgical instrumentation.

METHODS

An institutional review board–approved retrospective review of all patients undergoing surgery for NF1, NF2, and SWN was conducted. Both pediatric and adult patients were included in the analysis from 2009 to 2021. A total of 151 patients underwent excision of a cumulative 410 PNSTs during this time frame. Patients with malignant, dermal, or cutaneous neurofibromas were excluded to maintain a homogeneous study cohort. Only benign PNSTs, including neurofibromas and schwannomas, were included in the final analysis. Chart review included documentation of patient demographic factors, details of clinical presentation, and surgical details, including the use of magnification or the requirement for nerve repair. Pathology and postoperative complications were also documented. Tumor size was defined by the largest measured dimension for each resected specimen.

Workup of patients presenting typically includes preoperative imaging, most often magnetic resonance imaging with T2-weighted and short tau inversion recovery sequences. For cases with larger tumors in which a malignant PNST is suspected, a positron emission tomography scan is performed, particularly in instances of rapid tumor growth. In addition to imaging, each patient’s case is presented at an institutional neurofibromatosis multidisciplinary conference. The decision for resection of the tumors is primarily based on symptoms such as pain or an increase in tumor size. The patient is appropriately positioned on the operating room table to ensure safe patient positioning and ideal exposure for the operative field. Patients are induced under general anesthesia without muscle relaxants, and intravenous perioperative antibiotics are commonly administered. When a lesion is located on a distal extremity, a tourniquet is typically applied for the operation. Initial surgical steps focus on identifying the tumor and achieving proper intraoperative exposure. An incision is made, and dissection is carried down with the aid of electrocautery until the tumor is exposed. The affected nerves are identified and isolated both proximally and distally with vessel loops. Intraoperative nerve electrodiagnostics are used to identify and differentiate motor and sensory nerve fascicles. Direct nerve stimulation is used when exclusively motor fascicles are involved. Nerve monitoring is not used in plexiform lesions, in tumors localized to the digital nerves, or in masses in pure sensory or cutaneous nerves. Neurolysis is performed as appropriate for dissection and isolation of the involved fascicles. Tumors are excised en bloc with the capsule, when possible, and sent for pathological examination.

Using magnification, nerve repairs are performed as warranted by the case. Epineural repairs are performed in all cases. Interfascicular repairs are indicated only in cases where the nerve fascicles are disrupted by tumor resection. Following appropriate hemostasis, the operative fields are closed in a layered fashion. Postoperative soft dressings are applied with instructions for immobilization and elevation of the affected extremity.

All statistical analyses were performed in R (RStudio version 12.1; R Core Team, 2025). Descriptive statistics were used to summarize data as mean ± SD or median (range, minimum–maximum), and categorical variable analyses were performed using the Fisher exact test. Significance was set at a P value of 0.05 or less.

RESULTS

A total of 78 operations were performed on 69 patients. In this cohort, 157 peripheral nerve tumors were excised. The average patient age at initial presentation was 38.2 ± 16.4 years (range, 9–81 y). A slight majority of patients were female (n = 39, 56.5%). Most patients were diagnosed with NF1 (n = 32, 41.0%) preoperatively, whereas the second most common diagnosis was NF2 (n = 19, 24.4%). Nine patients (11.5%) presented without a known syndromic neurofibromatosis diagnosis. Nearly 70% (n = 52) of patients presented to the initial surgical consultation with preoperative imaging (Fig. 1). Pain was the most common presenting symptom for patients requesting surgical management of the lesions, occurring in 82.1% (n = 64) of patients. Other symptoms reported included paresthesia, dysesthesia, and focal neurological weakness or deficits. No association was found between preoperative pain and preoperative diagnosis (P = 0.289). Mean and median follow-up after surgery for this cohort were 5.56 ± 12.8 and 0.64 months (range, 0–6.19 y), respectively (Table 1).

Fig. 1.

Preoperative imaging. A, Preoperative magnetic resonance imaging of right medial arm mass visualizing the schwannoma abutting the radial and ulnar nerves. Operative photographs from this case are shown in Figure 2. B, Preoperative magnetic resonance imaging of sciatic nerve neurofibroma. Operative photographs from this case are shown in Figure 3.

Table 1.

Preoperative Baseline Characteristics for Patients Presenting With PNST Resection

Variable (N = 78)	n (%)
Preoperative diagnosis
NF1	32 (41.0)
NF2	19 (24.4)
SWN	18 (23.1)
None	9 (11.5)
Preoperative imaging
Yes	52 (66.7)
No	26 (33.3)
Predominant presenting symptom
Pain	64 (82.1)
Other	14 (17.9)
Mean follow-up ± SD, mo	5.56 ± 12.8
Median follow-up (range), mo	0.64 (0–6.19 y)

NF, neurofibroma; SWN, schwannoma.

Lesions were most frequently observed in the upper extremity (Figs. 2, 3), accounting for nearly half of tumors (n = 38, 48.7%) (Table 2). Lower extremity lesions were present in 29.5% (n = 23) of cases (Table 2). A minority of peripheral nerve tumors were resected from the trunk (n = 3, 3.8%) as well as the head and neck (n = 1, 1.3%). A total of 13 (16.7%) cases had peripheral nerve tumors in multiple locations. The average number of tumors excised per case was 2.04 ± 1.59 (range, 1–9). All cases used magnification and microsurgical instrumentation. Intraoperative nerve monitoring was used in 55.1% (n = 43) of cases, and nerve repair following tumor resection was required in 46.2% (n = 36) of cases (Fig. 5). Cases not requiring IONM were incidents of cutaneous nerves, digital nerves, or pure sensory nerves. When nerve repair was indicated, epineurial repair was sufficient in 86% (n = 31) of cases, whereas 14% (n = 5) required fascicular coaptation. From the cases of fascicular repair, 1 patient required a sural nerve graft to span the defect. In a separate case, a synthetic nerve wrap was used around the nerve coaptation (Table 2). A complete table of all cases involving nerve repair, including preoperative and postoperative pain, weakness, and paresthesia status, is provided in Supplemental Digital Content 1. (See table, Supplemental Digital Content 1, which details specific nerves repaired, repair type, and patient outcomes for each operation, https://links.lww.com/PRSGO/E921.)

Fig. 2.

Upper expremity, axillary peripheral nerve sheath tumor. A, Preoperative markings of the right medial arm. B, Triceps muscles retracted, exposing the mass. C, A 4-cm diameter schwannoma within the posterior cutaneous nerve of the arm. D, Excess capsule excised. E, Epineural nerve repair. F, The tumor and excess capsule.

Fig. 3.

Upper extremity forearm peripheral nerve sheath tumor. A, Preoperative magnetic resonance imaging demonstrating the tumor of the median nerve in the forearm. B, Tumor exposure after superficial dissection. C, Tumor exposed following dissection through the pronator muscle. D, Fascicular connections coursing through the tumor. E, Image of the excised tumor. F, Completion of epineural repair for reconstruction of the median nerve.

Table 2.

Tumor Characteristics, Operative Factors, and Postoperative Complications for Patients Undergoing PNST Resection

Variable (N = 78)	n (%)
Location of tumor
Upper extremity	38 (48.7)
Lower extremity	23 (29.5)
Trunk	3 (3.8)
Head and neck	1 (1.3)
Multiple regions	13 (16.7)
Size of tumor
0–1.9 cm	12 (15.4)
2–4.9 cm	42 (53.8)
5–9.9 cm	14 (17.9)
>10 cm	9 (11.5)
Unspecified	1 (1.3)
Average no. tumors excised	2.04 ± 1.59
Tumor pathology
NF	44 (53.0)
SWN	33 (39.8)
Other	6 (7.2)
Use of magnification
Yes	78 (100)
No	0 (0)
Intraoperative nerve monitoring
Yes	43 (55.1)
No	35 (44.9)
Nerve repair performed
Yes	36 (46.2)
No	42 (53.8)
Nonneurological-related complications	2 (2.7)
Postoperative neurological symptoms	13 (16.7)
New onset postoperative weakness	5 (6.4)
New onset postoperative pain	4 (5.1)
Postoperative paresthesia	10 (12.8)

NF, neurofibroma; SWN, schwannoma.

Fig. 5.

Intraoperative nerve monitoring. Representative tracing of intraoperative electromyography nerve monitoring of the sciatic nerve through direct stimulation in the case presented in Figure 4.

Fig. 4.

Sciatic nerve peripheral nerve sheath tumor. A, Sciatic nerve tumor exposed by dissection of the posterior thigh. B, Close-up image of the tumor. C, Excised neurofibroma measuring 3 cm in diameter. D, Depiction of the nerve in continuity following epineural repair.

Pathological analysis revealed that the majority of excised lesions were neurofibromas (n = 44, 53.0%). Schwannomas represented 39.8% (n = 33) of resected tumors, whereas 7.2% (n = 6) of lesions had mixed features or other pathologies. Over half of all tumors (n = 42, 53.8%) were between 2.0 and 4.9 cm, and 11.5% (n = 9) measured larger than 10 cm.

Two complications occurred (2.6%), both were surgical site dehiscence, and 1 required return to the operating room. A total of 13 cases (16.7%) reported neurological symptoms following resection. These included 5 cases (6.4%) of reported postoperative weakness at the first postoperative visit that was not present before the operation. These 5 cases improved over time; some patients took longer to recover than others, but all recovered over time. Ten (12.8%) patients experienced postoperative paresthesia. Only 4 (5.1%) patients complained of new onset pain at the surgical site during the perioperative period, with the remainder reporting improvement or resolution of their pain following tumor resection (Table 2). No correlation was observed between tumor size, pathology, or use of intraoperative nerve monitoring and complication rates, including postoperative pain, weakness, paresthesia, or surgical complications (P > 0.05).

DISCUSSION

PNSTs present a difficult reconstructive challenge to peripheral nerve surgeons. Patients may present with severe neurological symptoms, including pain, sensory deficits, and motor impairment in the affected nerves. Medical management alone has been established as ineffective in resolving symptoms for patients; thus, resection is often required.^7,12 Historical reports of PNST resections have documented high rates of patient morbidity, including both neuromotor and neurosensory loss of function, though importantly, nerve reconstruction was not commonly performed in those cohorts.¹³ We report our series of PNST surgical management at a tertiary referral center during a 13-year period, with a low complication profile. Our surgical technique can be simplified to 6 key practical pearls for addressing PNSTs: IONM, tourniquet control of the extremity, magnification and use of microsurgical instruments, enucleation from the tumor capsule in cases of NF2, epineural repair, and fascicular repair when there is interfascicular resection (Table 3).¹ Each of these steps enables a more efficient operation while simultaneously seeking to reduce postoperative patient morbidity. Practical application of these key pearls varies on a case-by-case basis. IONM can be most useful in cases where fascicular involvement may require a more complex dissection. Tourniquet control can improve visualization in distal extremity cases by ensuring a dry field and adequate hemostasis. Magnification and microsurgical instruments are essential across all settings, particularly for scarred or multifocal disease. Enucleation is ideal for schwannomas, but neurofibromas may require interfascicular dissection. Epineural repair restores nerve continuity and may be reinforced in revision cases, and fascicular repair, or grafting when needed, optimizes function when fascicles are transected. Collectively, these principles provide a reproducible framework adaptable to diverse patient populations and tumor characteristics.

Table 3.

Technical Recommendations for PNST Resection

Technical Pearls
Intraoperative nerve monitoring
Bloodless operation with tourniquet control
Magnification with microsurgical instrumentation
Enucleation from the tumor capsule (NF2)
Epineural repair
Interfascicular repair when indicated

There are several unique technical considerations that merit further discussion. In the majority of cases, we use IONM to facilitate preservation of noninvolved nerve fascicles when resecting a PNST, though there remains controversy surrounding its use. Debate in PNST resection centers on whether IONM truly reduces postoperative neurological deficits. Despite its theoretical benefits and widespread adoption, studies suggest comparable complication rates between monitored and nonmonitored cases.

Multiple studies have found no significant difference in neurological outcomes with IONM. In a series of 221 spinal nerve sheath tumors, complication rates were similar between monitored and nonmonitored groups, though IONM was associated with higher gross-total resection rates.¹⁴ Likewise, in 46 lumbar intradural schwannomas, IONM did not affect postoperative motor outcomes.¹⁵ Another study of intradural extramedullary tumors reported comparable new deficit rates between monitored and historical controls.¹⁶ Furthermore, IONM can have increased false positives for motor nerves secondary to increased tourniquet time, as well as transient deficits.^16,17

Proponents for IONM cite its predictive value and ability to guide intraoperative decision-making. IONM demonstrates high sensitivity and specificity for predicting postoperative deficits, with a positive-predictive value and negative-predictive value of 100% and 97%, respectively.¹⁶ In roughly 7% of cases, significant IONM changes prompted surgical modification that may have prevented injury.¹⁸ Motor-evoked potential decreases have influenced surgeons to limit dissection when further resection risked permanent deficits.^17,19

There are certain factors that should be considered when deciding whether to use IONM. First is the tumor type, in which IONM may be more valuable for neurofibromas than schwannomas, given their intimate fascicular involvement and higher deficit risk.²⁰ Additionally, revision cases, where prior surgery has been shown to increase deficit risk, may support selective IONM use.²⁰ This knowledge can also help guide postoperative rehabilitation protocols and patient counseling. Although IONM has not been definitively shown to reduce overall complication rates, it remains a common adjunct for complex or high-risk cases, especially those involving large tumors, critical nerve locations, or revision surgery.

In cases where the PSNT is known to be isolated to a motor nerve or when some perioperative factor precludes the use of intraoperative electrodiagnostics, a checkpoint nerve stimulator can be used to identify motor nerves. A key pearl is to position the patient such that the effect of electrostimulation can be observed in the extremity of interest.¹²

In a large series of PNSTs during a 30-year period, Kim et al⁴ described the importance of using fascicular dissection at the periphery of the tumor to mitigate damage to uninvolved fascicles. Sound surgical technique is required during dissection and removal of the tumor, and subsequent reconstruction is equally important. Following resection of NF1 tumors involving the fascicles, interfascicular coaptation is critical for nerve reconstruction.⁸ We have found that nerve grafting is typically not necessary, as tensionless re-approximation of the transected fascicular endings can be readily accomplished. In all cases, tension-free epineural coaptation is important to facilitate nerve regeneration and ultimately decrease postoperative sensitivity of the nerve.^21–23 Furthermore, epineural repair following mass excision has been demonstrated to improve symptoms and improve patients’ self-reported quality of life.²⁴ In a large series of more than 200 PNSTs, Guha et al²⁵ found that, similar to the present study, preoperative neurological complaints were not uncommon, and pain was the most frequent presenting symptom for patients. In their review, patients frequently had postoperative neurological sequelae, either in the form of motor, sensory, or neuropathic deficits.²⁵ Patients should be counseled that although in many cases these symptoms often improve, there is no guarantee that symptoms will disappear, and new neurological deficits may be caused by removing the tumor based on the extent of its nerve involvement.

Preoperatively, it is important to discuss all possibilities and risks with the patient. Patients should be aware of the potential for motor or sensory deficits following surgical excision of the tumor. They should likewise be counseled on the delayed nature of nerve regeneration and return of nerve function. In cases where the size or location of the tumor may prevent direct coaptation of the nerve following excision, patients should be informed of the possibility of a nerve graft. Given the tissue expansion–like effects of the growing tumor, there is generally sufficient laxity in the nerve endings to allow for primary coaptation. We have only performed nerve grafting in 1 patient early in our series.

Limitations of this study include its retrospective nature, and all statistical findings should be interpreted with caution given the limited sample size and low complication rate. This study also reflects a single surgeon’s experience and technical expertise. Other important metrics, such as quality-of-life outcomes, have been reported separately and were not included in this report.

CONCLUSIONS

This retrospective case series describes a single-surgeon experience with PNST excision, highlighting 6 key technical pearls: IONM, tourniquet control, magnification and microsurgical instrumentation, enucleation where applicable, and epineural and/or fascicular repair. Within the limitations of a level IV study, our findings suggest that these microsurgical principles can be applied to achieve low complication rates and favorable functional outcomes. Future prospective and comparative studies are needed to further validate these techniques and define their role across broader patient populations.

DISCLOSURE

The authors have no financial interest to declare in relation to the content of this article.