Upfront Gamma Knife surgery for facial nerve schwannomas: retrospective case series analysis and systematic review

INTRODUCTION

Facial nerve schwannomas are rare tumors and account for less than 2% of intracranial neurinomas, despite being the most common tumors of the facial nerve. The optimal management is currently under debate and includes observation, microsurgical resection, radiosurgery (RS), and fractionated radiotherapy. Radiosurgery might be a valuable alternative, as a minimally invasive technique, in symptomatic patients and/or presenting tumor growth.

METHODS

We review our series of four consecutive cases, treated with Gamma Knife surgery (GKS) between July 2010 and July 2017 in Lausanne University Hospital, Switzerland. Clinical and dosimetric parameters were assessed. Radiosurgery was performed using Leksell Gamma Knife Perfexion. We additionally performed a systematic review, which included 23 articles and 193 treated patients from the current literrature.

RESULTS

The mean age at the time of the GKS was 44.25 years (median 43.5, range 34-56). Mean follow-up period was 31.8 months (median 36, range 3-60). Two cases presented with facial palsy and other two with hemifacial spasm. Pretherapeutically, House-Brackmann (HB) grade was II for one case, III for two, and VI for one. The mean gross tumor volume (GTV) was 0.406 ml (median 0.470 ml, range 0.030-0.638 ml). The mean marginal prescribed dose was 12 Gy at the mean 54% isodose line (median 50%, range 50-70). The mean prescription isodose volume (PIV) was 0.510 ml (median 0.596 ml, range 0.052-0.805 ml). The mean dose received by the cochlea was 4.2 Gy (median 4.1 Gy, range 0.1-10). One patient benefited from a staged-volume GKS. At last follow-up, tumor volume was stable in one and decreased in three cases. Facial palsy remained stable in two patients (one HB II and one HB III) and improved in two (from HB III to II and from HB VI to HB III). Regarding hemifacial spasm, both patients presenting one pretherapeutically had a decrease in its frequency and intensity after GKS. All patients kept stable Gardner-Robertson class 1 at last follow-up.

CONCLUSION

In our experience, RS and particularly GKS, using standard, yet low doses of radiation, appear to be a safe and effective therapeutic option in the management of these rare tumors. The results as from our systematic review are also encouraging with satisfactory rates of clinical stabilization and/or improvement and high rate of tumor control. Complications are infrequent and mostly transient.

Stripping surgery in facial nerve schwannomas with favorable facial nerve function

OBJECTIVE

We report 18 cases of facial nerve schwannomas in which stripping surgery was attempted to preserve facial nerve integrity and favorable facial nerve function.

METHODS

We attempted stripping surgery on 18 cases of facial nerve schwannomas. Postoperative facial nerve function was evaluated.

RESULTS

Stripping surgery was successfully achieved in 11 cases, and facial nerve decompression was performed on the remaining 7 cases in which stripping surgery was impossible. Favorable facial nerve function was successfully maintained in all cases who underwent stripping surgery and 5 of 7 cases who underwent facial nerve decompression.

CONCLUSIONS

It was possible to accomplish stripping surgery in most cases with favorable facial nerve function, which maintained good facial nerve function after total tumor removal.

Stripping surgery in intratemporal facial nerve schwannomas with poor facial nerve function

To report stripping surgery in intratemporal facial nerve schwannomas (FNS) with poor facial nerve function.

METHODS

We attempted stripping surgery to completely remove intratemporal FNS with nerve intact in 17 patients, and succeeded in 12 cases. Clinical features of the tumors and the surgical approach were discussed.

RESULTS

Multi-segment involvement was present in 10 cases (58.8%). The tumors were completely removed in all cases, and facial nerve integrity was preserved in 12 patients (70.6%). Six of 12 cases (50.0%) with nerve intact obtained acceptable facial nerve recovery, two of which recovered to Grade II, compared to 2 of 5 cases (40%) with nerve grafting.

CONCLUSIONS

Multi-segment involvement was more common in FNS. Stripping surgery could remove tumor completely with nerve intact in majority patients, and it seemed to obtain better outcomes of facial nerve.

Near-total removal of facial nerve schwannomas: long-term outcomes

OBJECTIVE

The study aimed to present long-term outcomes of near-total removal of facial nerve schwannomas (FNS) with good facial nerve function (HB Grade III or better).

METHODS

We successfully performed near-total removal of FNS (tumor removal of 95% or greater) on 13 cases, and the remaining 6 cases who failed underwent total tumor removal and nerve grafting. Patients were divided into near-total removal group and total removal group according to surgical approach, and they were followed up for 7.38 ± 1.98 years (range, 5 to 11 years) and 6.66 ± 1.63 years (range, 5 to 9 years), respectively.

RESULTS

12 of 13 cases (92.3%) in the near-total removal group successfully maintained at least Grade III except one who recurred and underwent complete tumor removal and nerve grafting, and 10 cases (76.9%) achieved Grade I or Grade II. 5 of 6 cases (83.3%) in the total removal group obtained Grade III, but none recovered to Grade I or II. Tumor growth was noted in only one case (7.7%) among the near-total removal group during the follow-up.

CONCLUSIONS

Long-term outcomes of near-total removal of FNS were favorable, which may be a good choice for the old patients with good facial nerve function.

Long-term outcomes of facial nerve schwannomas with favorable facial nerve function: tumor growth rate is correlated with initial tumor size

OBJECTIVE

The study aimed to report long-term outcomes of facial nerve schwannomas (FNS) with favorable facial nerve function by observation, and to discuss about the relationship between initial tumor size and tumor growth.

METHODS

21 facial nerve schwannoma cases with favorable facial nerve function were managed by observation. They were divided into larger size group (size ≥10mm) and smaller size group (size <10mm) according to initial tumor size.

RESULTS

They were followed up for 6.4±1.7years. 18 of 21 cases (85.7%) maintained House-Brackmann Grade III or better. Growth rate of the tumors in larger size group was 72.7%, much higher than 10% in smaller size group (p<0.05).

CONCLUSIONS

Observation was feasible for most FNS with favorable facial nerve function, and growth rate of the tumors was associated with tumor size.

Subtotal resection of facial nerve schwannoma is not safe in the long run

CONCLUSIONS

Subtotal resection of facial nerve schwannoma (FNS) could obtain favorable facial nerve function recovery, but has a high recurrence rate in the long run. Subtotal resection with about 95% tumor resected could be considered in the elderly with good facial nerve function, but is not recommended for younger patients. Subtotal resection with about 70-80% tumor resected should be replaced by complete tumor removal and nerve grafting.

OBJECTIVES

To present long-term follow-up results of subtotal resection of FNS and discuss the indications for subtotal resection.

METHODS

We performed subtotal resection of FNS in 15 cases and they were followed up for 7 years on average.

RESULTS

In all, 93.3% of cases finally gained normal or near-normal facial nerve function (House-Brackmann (HB) grade I or II) and one case maintained grade III. Tumor recurrence or regrowth was noted in four cases (26.7%) during follow-up. Recurrence was observed in 10% of cases who had about 95% tumor resected and in 60% of cases who had 70-80% tumor resected.

Collision tumor of the facial nerve: a synchronous seventh nerve schwannoma and neurofibroma

OBJECTIVE

To report a novel case of a collision tumor involving an intraparotid neurofibroma and a mastoid segment facial nerve schwannoma.

STUDY DESIGN

Clinical capsule report.

SETTING

Tertiary academic referral center.

PATIENT

A 29-year-old woman with a 2-year history of an asymptomatic enlarging left infraauricular mass and normal FN function presented to a tertiary care referral center. Computed tomography and magnetic resonance imaging demonstrated a cystic lesion in the deep portion of the parotid gland extending into the stylomastoid foramen.

INTERVENTION

The patient underwent superficial parotidectomy, and a cystic parotid mass was found to be intrinsic to the intraparotid facial nerve. A portion of the mass was biopsied, and intraoperative frozen section pathology was consistent with a neurofibroma. A mastoidectomy with FN decompression was then performed until a normal-appearing segment was identified just proximal to the second genu. After biopsy, proximal facial nerve stimulation failed to elicit evoked motor potentials, and en bloc resection was performed.

RESULTS

Final pathology demonstrated a schwannoma involving the mastoid segment and a neurofibroma involving the proximal intraparotid facial nerve.

CONCLUSION

We report the first case of a facial nerve collision tumor involving an intraparotid neurofibroma and a mastoid segment facial nerve schwannoma. Benign FN sheath tumors of the parotid gland are rare but should be considered in the differential diagnosis of a parotid mass.

The intraparotid facial nerve schwannoma: a diagnostic and management conundrum

OBJECTIVES

The aims of the study were (1) to review the management strategy and clinical outcomes of all intraparotid facial nerve (FN) schwannomas (PFNSs) treated at a single tertiary academic center from 1975 to 2010 and (2) to summarize all previously reported cases of PFNS in the international literature.

STUDY DESIGN

A retrospective cohort study and literature review.

METHODS

Fifteen patients were diagnosed and treated at the authors' institution from 1975 to 2010. In addition, 124 published cases were systematically reviewed.

RESULTS

The most common presentation of PFNS was a painless parotid mass with normal FN function. Eccentric, loosely attached intraparotid tumors underwent gross total resection with nerve preservation granting satisfactory postoperative FN function, whereas "inseparable" intraparotid tumors were observed in 8 cases with stable long-term size. Lesions that extended into the fallopian canal underwent complete resection with FN sacrifice and nerve grafting in 10 cases, whereas 1 patient received subtotal resection of the intraparotid portion with stereotactic radiotherapy targeting the intratemporal component.

CONCLUSIONS

Intraparotid FN schwannomas present similar to other primary salivary gland neoplasms, making an early diagnosis challenging. Intraoperative recognition of gross tumor characteristics and early histologic diagnosis with strategic biopsy are critical. Information including tumor location and extent, preoperative FN function, and the gross relationship between the tumor and the FN may guide the surgeon toward an optimal treatment plan emphasizing long-term neurologic preservation.

Management Outcomes of Facial Nerve Tumors

Objectives

Primary facial nerve tumors (FNTs) present in varying ways. In this study, the authors present their institutional experience with the management of facial nerve tumors, including their recommendations for available therapies such as observation, microsurgical decompression or removal, and stereotactic radiation. They emphasize the auditory and facial nerve function outcomes.

Study Design

Retrospective case review.

Setting

Tertiary referral center.

Subjects and Methods

Retrospective review of all cases of FNT seen at the authors’ tertiary care academic medical center over a 10-year period (2002-2011). The clinical presentation, treatment modality, and outcome parameters of cochlear and facial nerve function were assessed.

Results

Twelve patients were identified. House-Brackmann grades on presentation were 4 grade I, 2 grade II, 2 grade III, 1 grade IV, and 3 grade V, with 2 grade V patients declining to grade VI shortly after presentation. Seven patients presented with serviceable hearing and 4 with nonserviceable hearing. Treatment options/arms included observation with serial clinicoradiological review (2 cases), stereotactic radiation with the CyberKnife (3 cases), wide fallopian canal decompression (3 cases), microsurgical excision and repair (3 cases), and biopsy followed by observation (1 case). At the end of the review period, facial nerve function was stable in 8 patients, improved in 3, and declined in 1, and none had documented worsening of hearing based on American Academy of Otolaryngology—Head and Neck Surgery Foundation classification.

Conclusions

Management of FNT is largely based on the clinicoradiological picture. Each treatment arm is different, but overall auditory and facial function can be maintained.

Gamma Knife surgery for nonvestibular schwannomas: radiological and clinical outcomes

OBJECT

Most intracranial schwannomas arise from cranial nerve (CN) VIII. Stereotactic radiosurgery is a mainstay of treatment for vestibular schwannomas. Intracranial schwannomas arising from other CNs are much less common. We evaluate the efficacy of Gamma Knife surgery on nonvestibular schwannomas including trigeminal, hypoglossal, abducent, facial, trochlear, oculomotor, glossopharyngeal, and jugular foramen tumors.

METHODS

Thirty-six patients with nonvestibular schwannomas were treated at the University of Virginia Gamma Knife center from 1989 to 2008. The median patient age was 48 years (mean 45.6 years, range 10-72 years). Schwannomas arose from the following CNs: CN III (in 1 patient), CN IV (in 1), CN V (in 25), CN VI (in 2), CN VII (in 1), CN IX (in 1), and CN XII (in 3). In 2 patients, tumors arose from the jugular foramen. The median tumor volume was 2.9 cm(3) (mean 3.3 cm(3), range 0.07-8.8 cm(3)). The median margin dose was 13.5 Gy (range 9.3-20 Gy); the median maximum dose was 30 Gy (range 21.7-50.0 Gy).

RESULTS

The mean and median follow-up times of 36 patients were 54 and 37 months, respectively (range 2-180 months). At the last radiological follow-up, the tumor size had decreased in 20 patients, remained stable in 9 patients, and increased in 7 patients. The 2-year actuarial progression-free survival was 91%. Higher maximum dose was statistically related to tumor control (p = 0.027). Thirty-three patients had adequate clinical follow-up. Among them, 21 patients had improvement in their presenting symptoms, 8 patients were stable after treatment with no worsening of their presenting symptoms, 2 patients developed new symptoms, and 1 patient experienced symptom deterioration. Notably, 1 patient with neurofibromatosis Type 2 developed new symptoms that were unrelated to the tumor treated with Gamma Knife surgery.

CONCLUSIONS

Gamma Knife surgery is a reasonably effective treatment option for patients with nonvestibular schwannomas. Patients require careful follow-up for tumor progression and signs of neurological deterioration.