An alternative treatment for facial nerve tumors: short-term results of radiotherapy.

Abstract

A review of medical records of patients undergoing radiotherapy for facial nerve tumors was undertaken to determine subsequent facial nerve results, hearing results, and tumor control. Two patients with facial nerve tumors received this treatment. Facial nerve function remains excellent in one patient and significantly improved in the other. Neither tumor demonstrated growth. Current philosophies of facial nerve schwannoma management attempt to balance tumor control with facial nerve function. Radiotherapy for these tumors appears to preserve short-term facial function and may be a viable alternative to surgical management.

Introduction

Stereotactic irradiation can be successfully used to limit or stop the growth of benign neoplasms of the skull base. Newer, low-dose protocols have decreased associated cranial nerve injuries, making stereotactic irradiation a useful alternative to microsurgical tumor excision in selected patients. In the posterior fossa, stereotactic irradiation is primarily used for the treatment of vestibular schwannomas or meningiomas using dosimetry designed to avoid cranial nerve morbidity, particularly to the facial nerve, while providing adequate dosing to control tumor growth.

Only one other report exists describing stereotactic irradiation specifically for the treatment of a facial schwannoma. (1) Facial nerve neoplasms are not typically selected for treatment with this modality because of the concern that direct irradiation to the facial nerve could cause significant and permanent facial nerve dysfunction. (2) In this article, we present the short-term outcomes of 2 patients who underwent stereotactic irradiation to known facial nerve neoplasms.

Patients and methods

A retrospective review of charts from 1998 to 2005 identified 11 patients with the diagnosis of facial nerve neoplasms treated in our practice. Two of these patients underwent stereotactic irradiation for treatment of their tumors. Both patients have had at least 2 years of followup, which has included post-treatment radiographic imaging to assess tumor response.

Results

Case 1. Patient 1 was a 53-year-old man initially treated at an outside institution for what was thought to be a right internal auditory mass and a separate temporal meningioma on the same side. These tumors were diagnosed via magnetic resonance imaging (MRI) 5 years prior to our first evaluation of this patient. The original MRI was ordered to evaluate the patient for Meniere disease diagnosed on the opposite ear; the tumors were an incidental finding. Interestingly, this patient had a history of sudden-onset, right-sided facial nerve paralysis with rapid spontaneous resolution prior to his initial workup. He was initially opposed to any therapy for these tumors; therefore, the referring physician elected to follow them with serial MRI. He was referred 5 years later to our practice because of progressive growth of the right temporal mass.

The patient was asymptomatic on initial evaluation at our practice. His Meniere disease had caused vertigo spells and hearing fluctuation typical of this disorder in the past, but it was not active for several years prior to our evaluation. His cranial nerve examination was normal, with normal bilateral facial nerve function. Audiometry demonstrateda speech-reception threshold (SRT) of 15 dB and a speech-discrimination score (SDS) of 96% on the right (tumor side), with an SRT of 55 dB and SDS of 80% on the left. His original MRI scans 5 years earlier had revealed the right-sided temporal and internal auditory canal lesions, which were 7 mm and 10 mm, respectively, in maximum dimension. Sequential MRIs were performed three times prior to our evaluation, each demonstrating slow but progressive growth of the temporal tumor. The MRI just prior to our evaluation revealed the temporal mass to be 1.8 cm in maximum diameter, with no change in the size of the internal auditory canal mass over 5 years (figure 1).

[FIGURE 1 OMITTED]

The patient was extensively counseled regarding his treatment options, which included continued observation, stereotactic irradiation, and surgical excision. He elected to undergo tumor removal via a middle fossa approach. The goal was removal of the growing temporal mass with internal auditory canal decompression for the nongrowing internal auditory canal mass, without excision, given that this was his significantly better hearing ear.

A middle fossa craniotomy was performed, and the temporal mass was easily identified during dural elevation. This mass was firmly attached to the geniculate fossa and was separate from the dura. This prompted suspicion that the mass was, in fact, part of a facial nerve tumor and not a separate meningioma. The mass was confirmed as a facial nerve schwannoma by neural probe stimulation. The case was electively terminated without tumor excision so that we could properly discuss this specific pathology with the patient.

After seeking outside opinions at two other institutions, the patient elected to have his facial nerve schwannoma treated by stereotactic irradiation despite our expressed opinion to him that irradiation could deteriorate his hearing on the treated side. He underwent fractionated radiation treatment of the tumor with 5 fractions of 500 cGy per fraction once per day for 5 days, delivering a total of 2,500 cGy.

The patient has been followed for 3 years since radio therapy treatment. The geniculate portion of the tumor remained stable in size 3 years after treatment. The tumor size before therapy was 18 mm anterior to posterior, 18 mm lateral to medial, and 15 mm superior to inferior. The tumor was 19 x 18 x 14 mm, respectively, on his most recent MRI. His facial nerve function has remained at House-Brackmann grade I/VI over this time. He does have a documented progressive hearing loss on the same side, with his average pure tone threshold decreasing from 23 dB to 54 dB and discriminiation decreasing from 96% to 44%.

Case 2. Patient 2 was a 51-year-old man who was sent to our practice for left-sided hearing loss and acute-onset facial nerve paralysis. On initial evaluation, he had House-Brackmann grade VI/VI left-sided facial nerve paralysis. Audiometry revealed an asymmetric sensorineural hearing loss with an SRT of 15 dB and an SDS of 100% in the right ear, and an SRT of 20 dB and SDS of 100% in the left (affected) ear. MRI revealed an enhancing 4 mm x 2 mm left internal auditory canal lesion (figure 2). Additionally, the geniculate ganglion and tympanic segment of the facial nerve also had greater contrast uptake than the opposite side, indicating tumor in these sections. Electroneurography showed a 98% weakness compared to the other side, and electromyography revealed fibrillation potentials in the oculi, frontalis, and oris muscles.

After comprehensive consultation regarding treatment options, the patient elected to proceed with stereotactic irradiation. He was counseled regarding concerns that nerve grafting would likely be necessary to restore lost facial nerve function, but he insisted that he did not want to undergo surgical treatment that would take him away from his work. He therefore underwent treatment with single-dose stereotactic irradiation delivered by a linear accelerator with 1,200 cGy prescribed to the 90% isodose line.

[FIGURE 2 OMITTED]

This patient has been followed for 24 months since treatment. His last MRI showed no tumor growth. Interestingly, his facial nerve function significantly improved 3 months after treatment, and on his last follow-up, his facial nerve function was at House-Brackmann grade III/VI. Audiometry has demonstrated a significant decrease in auditory thresholds, however, with his pure tone average decreasing to 46 dB and his SDS decreasing to 80% in the left ear at 2 years post-treatment.

Discussion

Facial schwannomas are very slow growing and are often diagnosed in patients with normal facial nerve function. In addition, facial schwannomas are often integrated into the axons of the nerve, making preservation of the facial nerve difficult during surgical excision. Many authors therefore advocate a period of observation, with surgical intervention if facial nerve function is compromised by the tumor or if the tumor demonstrates significant growth? Other authors suggest that excision should be performed while the tumor is still very small so that the probability of preserving the facial nerve is increased. (4) Regardless of management philosophy, these tumors remain a therapeutic challenge because of the risk of facial nerve injury--either from progressive growth of the tumor or from surgical trauma.

The authors are only aware of one other case report of stereotactic irradiation used for the treatment of facial schwannoma. (1) Apprehension regarding the use of stereotactic irradiation for these tumors is fueled by legitimate concerns that radiation can induce microvasculitis and axonal degeneration in target neural tissue? Stereotactic irradiation is an accepted treatment for vestibular schwannomas, however, with facial nerve and hearing results comparable to those attained with surgery. (6) Lower-dose protocols and improved dosimetry planning continue to lower cranial nerve complications. (7) Most protocols for vestibular schwannomas attempt to minimize radiation exposure to the facial nerve in an effort to decrease the risk of paralysis, although in reality this is difficult given the close approximation of the facial nerve to these tumors.

Stereotactic irradiation can be delivered either in a single fraction or in multiple fractions. Both technical and radiobiologic rationales exist for these approaches. Technically, linear-accelerator-based radiotherapy systems allow for single-fraction or fractionated treatment. The Gamma knife is limited to single-fraction therapy. From a radiobiologic standpoint, there is established value to fractionation in limiting damage to normal structures by allowing for repair of sublethal damage to normal tissues that occurs between fractions. In order to deliver a radiobiologically equivalent dose to the tumor, higher total doses of radiation are delivered with a fractionated approach (i.e., 2,500 vs. 1,200 cGy in this review). Both techniques have an established indication for the treatment of acoustic neuromas.

The mainstay of facial nerve schwannoma treatment at Pittsburgh Ear Associates continues to be a period of observation followed by surgical tumor excision and potential facial nerve grafting if the tumor is growing or if facial nerve function has clinically deteriorated. The 2 unusual cases presented in this report, in which the patients specifically chose to undergo radiotherapy, entertain the question of whether radiotherapy for facial nerve schwannomas may be a legitimate therapeutic alternative to this approach. In both cases, the patients were offered surgery or observation, but for various reasons they elected to undergo stereotactic irradiation. Both tumors appear to be controlled over the first few years, but no conclusive statement can be made about long-term control. We assume that control rates for these facial nerve schwannomas would be similar to those for vestibular schwannomas, but this assumption is not supported by the literature or this study.

The critical observation in this series is that facial nerve function has been stable or improved in our 2 patients following radiotherapy. Despite concerns about intentional and direct irradiation to the facial axons, Patient 1 continues to have House-Brackmann grade I function more than 3 years post-treatment, and Patient 2 improved substantially from a House-Brackmann grade VI to a grade III in a matter of 12 months after surgery. Improvements in dosimetry planning, lower radiation doses (12 Gy in Patient 2), and fractionation (Patient 1), have likely decreased neural morbidity substantially, contributing to these results. Another important observation is that both patients have significant hearing loss in the treated ear, a likely effect of irradiation.

Although stereotactic irradiation may be a valuable alternative to surgical intervention for facial nerve schwannomas, the authors still recommend a period of observation with surgical intervention for demonstrated tumor growth or progressive facial nerve function deterioration, for the following reasons:

1. Long-term stereotactic irradiation tumor-control rates are not known.

2. Long-term facial nerve function results are not known.

3. Surgical intervention maybe more difficult after irradiation, and graft-take rates may be affected. (8)

4. There is concern about malignant transformation, especially in young patients. (9,10)

Radiotherapy for facial schwannomas remains an excellent alternative for older patients and for patients with medical contraindications for surgery. These indications may broaden once longer-term follow-up data become available. Therefore, this approach warrants further investigation.

References

(1.) McClelland S 3rd, Dusenbery KE, Higgins PD, Hall WA. Treatment of facial nerve neuroma with fractionated stereotactic radiotherapy. Stereotact Funct Neurosurg 2007;85(6):299-302.

(2.) House JW, Brackmann DE. Facial nerve grading system. Otolaryngol Head Neck Surg 1985;93(2):146-7.

(3.) Liu R, Fagan P. Facial nerve schwannoma: Surgical excision versus conservative management. Ann Otol Rhinol Laryngol 2001;110 (11):1025-9.

(4.) Perez R, Chen JM, Nedzelski JM. Intratemporal facialnerve schwannoma: A management dilemma. Otol Neurotol 2005;26(1):121-6.

(5.) Watanabe T, Saito N, Hirato J, et al. Facial neuropathy due to axonal degeneration and microvasculitis following gamma knife surgery for vestibular schwannoma: A histological analysis. Case report. J Neurosurg 2003;99(5):916-20.

(6.) Kaylie DM, Horgan MJ, Delashaw JB, McMenomey SO. A metaanalysis comparing outcomes of microsurgery and gamma knife radiosurgery. Laryngoscope 2000; 110(11): 1850- 6.

(7.) Lunsford LD, Niranjan A, Flickinger JC, et al. Radiosurgery of vestibular schwannomas: Summary of experience in 829 cases. J Neurosurg 2005;102 Suppl:195-99.

(8.) Friedman RA, Brackmann DE, Hitselberger WE, et al. Surgical salvage after failed irradiation for vestibular schwannoma. Laryngoscope 2005;115(10):1827-32.

(9.) Shin M, Ueki K, Kurita H, Kirino T. Malignant transformation of a vestibular schwannoma after gamma knife radiosurgery. Lancet 2002;360(9329):309-10.

(10.) Lustig LR, Jackler RK, Lanser MJ. Radiation-induced tumors of the temporal bone. Am J Otol 1997;18(2):230-5.

Todd A. Hillman, MD; Douglas A. Chen, MD, FACS; Russell Fuhrer, MD

From Pittsburgh Ear Associates (Dr. Hillman and Dr. Chen) and the Department of Radiation Oncology, Allegheny General Hospital (Dr. Fuhrer), Pittsburgh.

Corresponding author: Todd A. Hillman, MD, Pittsburgh Ear Associates, 420 E. North Ave., Ste. 402, Pittsburgh, PA 15212. Phone: [phone]; fax: [phone]; e-mail: [e-mail]