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The advent of magnetic resonance imaging has allowed otologists to focus on the early removal of acoustic neuromas with the goal of hearing preservation. Clearly, there are some unpredictable factors, such as placement of the tumor in the medial vs the lateral segment of the internal auditory canal and the capricious nature of the blood supply to these benign neoplasms, that make prediction of hearing preservation difficult. Nonetheless, the present goal of surgery for removal of acoustic tumors has changed its focus from preservation of the facial nerve alone to preservation of the facial nerve and preservation of hearing. In a patient with an only-hearing ear and a small acoustic neuroma, there is some controversy concerning whether the tumor should be removed early, with the goal of hearing preservation, or if the patient should be allowed to progress to a considerable hearing loss in an effort to preserve natural hearing as long as possible. We report a case in which an acoustic tumor was removed from an only-hearing ear in a patient with neurofibromatosis after hearing loss had progressed in that ear but before the development of total deafness. Postoperatively, the patient successfully underwent cochlear implantation. We also discuss decisions that we made during the surgical procedure, as well as the feasibility of cochlear implantation in patients with profound deafness after the excision of acoustic neuromas.

Neurofibromatosis (NF) 2, associated with bilateral acoustic neurinomas has been shown to be an entity distinct from NF 1, since their chromosomal abnormalities are completely different. NF 2 has a very low occurrence rate, but would be a terrible disease by its high prevalence of offsprings. In addition, compared to the majority of unilateral, nonfamiliar neurinoma, acoustic neurinomas of NF 2 have been shown to be refractory to treatments. Therefore, it is crucial to know the clinical characteristics of patients with NF 2. In this study, we analyzed 14 cases of NF 2 and 7 cases of NF 1 in whom brain tumors are main symptoms. Brain tumors associated with NF 1 were five neurinomas, two gliomas and a meningioma. The mean age of NF 1 patients accompanied with brain tumors was 37.6 years old, younger than the overall age of NF 1 patients. In patients with NF 2 there was often association with cranial, and spinal neurinomas and meningiomas. NF 2 especially, in younger patients was accompanied with multiple spinal neurinomas. Twenty acoustic neurinomas in 14 NF 2 patients were treated by surgery. Operative results showed that total resection was achieved in only 5 cases, 13 were subtotally and 2 were partially resected. Hearing preservation was attained in only three cases. In addition, all but two patients were complicated with postoperative facial palsy. From this analysis, it is clear that NF 2-associated acoustic neurinomas are not responsive to surgical intervention. We also reviewed genetical problems briefly.

Bilateral acoustic neurinomas are found in almost all patients with neurofibromatosis 2 (NF2). With better knowledge of the disease and development of diagnostic procedures, an increasing number of patients have been detected at an early stage of the disease. Preservation of hearing in these cases has become more feasible. Between 1979 and 1992, 110 acoustic neurinomas in 74 NF2 patients have been resected in this department. All tumours but 11 were completely removed. In 11 cases deliberate subtotal tumour removal was performed: bilaterally in one deaf patient for brainstem decompression, and unilaterally in nine patients with the aim of hearing preservation. In seven of these nine cases hearing was preserved. The total rate of hearing preservation was 36%. Considering only those patients with good preoperative hearing and small tumours, the rate of hearing preservation was 58%. Facial nerve preservation was 92%. Nerve reconstructions were performed in cases of facial nerve damage, with good results in most of the cases. The importance of early detection of the disease and early removal of tumours is stressed. Surgical decision making based on the author's personal experience in dealing with these cases is discussed, and some cases are illustrated.

Twenty-seven of the 1560 patients treated by radiosurgery during the period 1984-1993 had acoustic neurinomas. Four cases were excluded from this study because they had a follow-up of less than 2 years. There were 24 neurinomas treated in 23 patients as one patient had a bilateral tumour. Seven patients underwent radiosurgery for a recurrent tumour (already operated on once or twice), while it was the first treatment for 16 patients. The tumour volume ranged from 1.99 cm3 to 18.30 cm3, and the patient follow-up was from 2 to 8 years. To determine the target on CT/NMR for linear accelerator stereotactic irradiation, the Greitz-Bergström non-invasive head fixation device was used. It was again adopted for subsequent serial imaging, and for repeat radiosurgery when necessary. The total peripheral tumour dose ranged from 12 to 45 Gy. In 9 patients there was a reduction in tumour volume varying from 39 to 100%, while 14 of the neurinomas appeared stable after an average follow-up of 3 years. In one patient there was an increase in size of the tumour. Variable morphological changes were present in 66% of the neurinomas treated. Radiosurgery is indicated as an alternative to microsurgery for inoperable patients and for those who refuse surgery, for recurrent tumours, and as a post-operative complementary treatment for partially removed tumours. A gradual approach to radiosurgery, depending on tumour response, allows a greater efficacy with minimal risk. In the present series no complications were observed. Hearing was preserved at almost the same level as that prior to radiosurgery in all patients.

Magnetic resonance imaging (MRI) is currently the 'gold-standard' investigation in patients with a unilateral sensorineural hearing loss. The procedure, however, is expensive and of limited availability. Instead, such patients often undergo a series of audiovestibular tests and computed tomography in an attempt to exclude or diagnose a vestibular schwannoma. We describe seven cases of unilateral vestibular schwannoma in which conventional assessment was either equivocal or failed to demonstrate a tumour subsequently diagnosed by magnetic resonance imaging. Two patients with neurofibromatosis type 2 are also reported to show how magnetic resonance imaging confirmed the presence of a second vestibular schwannoma despite CT that showed only a unilateral lesion. We also illustrate how limited protocol MRI of patients is slightly more expensive yet much more cost effective than the usual battery of tests and propose that it should be the first line investigation for patients in whom the clinical picture requires exclusion of a retrocochlear lesion. Not all of these early diagnosed tumours have been immediately removed. In some of the more elderly or infirm patients a 'wait and rescan' policy has been adopted. Nevertheless, the early establishment of the correct diagnosis facilitates the subsequent management of these patients.

The authors compared the long-term recovery of sutured facial nerves after the removal of 8 neurofibromatosis-2 (NF2)-associated and 22 non-NF2 acoustic neuromas. The patients were from a series of 270 patients operated on for an acoustic neuroma between 1979 and 1989. The assessment was done with a modified House and Brackmann scale from video recordings. At least some facial movement or tone was achieved (Grade 5 or better) in all but three patients, but in none was the recovery excellent. The facial function, judged by the overall appearance in movement, recovered less in patients with NF2 (P = 0.048); a moderately good recovery (Grade 3 or better) was seen in one patient of eight with NF2, as compared with 13 of 22 with non-NF2. In conclusion, if the tumor cannot be peeled off easily from the facial nerve in patients with NF2, leaving a fragment of tumor behind is preferable to cutting and suturing the facial nerve.

Hearing conservation in acoustic tumour surgery remains controversial. There have been few previous reports in the British literature. The senior author has managed 24 patients by retrosigmoid surgery with the intention of preserving hearing during the last 9 years. The clinical features, surgical technique and results are discussed with respect to pre-operative selection criteria, and post-operative quality of hearing. Hearing preservation has been achieved in 11 (78.6%) of 14 patients with small or intracanalicular tumours and a mean minimum auditory threshold of 35 dB and 70% speech discrimination, the majority (81.8%) above the 50 dB/50% level. Tumour filing the fundus of the internal auditory canal was found to be a significant adverse prognostic factor as regards successful hearing preservation. Tumour excision was complete in all patients. Nearly 90% of patients had normal facial function, and the remaining 10% grade II function. Associated morbidity was minimal. It is suggested that the potential for hearing conservation should be considered as a factor in the management of patients with small acoustic neuromas.

The primary aim of the auditory brainstem implant (ABI), an investigational device, is to restore auditory sensations in neurofibromatosis-2 patients deafened by bilateral acoustic neuroma surgery. An electrode is placed on the dorsal cochlear nucleus after the tumor is removed through the translabyrinthine approach. This procedure was performed on 18 patients: 13 were completely deafferentated after bilateral tumor removal and had received the ABI during surgery on the second-sided tumor; 5 were implanted at first-sided tumor removal. Three of these 5 patients had usable hearing remaining on the side of the second acoustic neuroma and were stimulated only during laboratory sessions. All patients had tinnitus. We used a questionnaire to assess the effects of brainstem stimulation on this symptom. Of the 18 patients, one early patient deceased, and one patient with no follow-up was not included in this study. Six patients who were unable to use the ABI because of temporary hardware problems or side effects from electrical stimulation were also excluded. Thus, we studied 10 patients. Of 7 patients who used their implant daily, 6 reported noticeable tinnitus reduction; the ABI had no effect in the remaining case. Of 3 recently implanted patients who used this implant only during laboratory testing, one patient reported complete suppression of tinnitus, one described worse tinnitus, and one reported no effect.

In acoustic neurinoma surgery, the surgeon is required to find a cleavage plane between the facial nerve and the tumor, and with the aid of the operating microscope this is usually achieved by fine dissection. A histological specimen of the nerve-tumor interface is available only if the facial nerve was hopelessly adherent to the tumor (usually a large or giant neoplasm) and the surgeon decided to sever the nerve to obtain a complete removal. The authors have examined immunohistochemically the nerve-tumor interface of 20 such facial nerves (six cases of neurofibromatosis 2 (NF2) and 14 of non-NF2) in a series of 351 acoustic neurinomas. The largest extrameatal dimension of the 20 tumors ranged from 20 to 51 mm (median 39 mm). In all of these 20 instances the nerve-tumor contact area was at least partially devoid of a clear-cut histological cleavage plane. Where the facial nerve trunk was attached to the surface of the tumor, nerve fibers of the contact areas either abutted directly against tumor cells or nerve fibers were seen to penetrate into the tumor tissue. Frank embedding of nerve fibers was more frequent in NF2.

Between 1979 and 1989, 13 patients with neurofibromatosis 2 underwent reconstructions of the facial nerve after removal of bilateral acoustic or facial neurinomas. Seven patients received hypoglossal-facial nerve anastomosis, and five received sural nerve grafting in the cerebellopontine angle. End-to-end anastomosis and intracranial-intratemporal sural grafting were performed for one patient each, respectively. Re-innervation was seen in all cases. The results were good in 11 cases. Two patients presented with poor results due to development of neurinomas close to the site of the nerve reconstruction. The importance of reconstructive surgery in patients with neurofibromatosis is stressed. The problems regarding failure of re-innervation in some cases and difficulties in their management are discussed.

Preservation of hearing was attempted in 161 cases of histologically confirmed acoustic neuroma removed by the senior author between January 1, 1970, and September 30, 1991. There were 136 patients with unilateral tumors; 22 patients had bilateral tumors (neurofibromatosis 2) and underwent a total of 25 procedures. Hearing was initially preserved in 35% of patients with unilateral tumors and in 44% of those with bilateral tumors. Results are reported in terms of pre- and postoperative pure tone average and speech discrimination scores. Surgical access to the tumor was obtained via middle cranial fossa and suboccipital approaches. The latter has been used more often over the past 5 years because of a lower associated incidence of transient facial paresis. Persistent postoperative headaches have been the most common complication following the suboccipital approach. The results of preoperative brain-stem auditory evoked response (BAER) studies were useful in predicting the outcome of hearing preservation attempts. Patients with intact BAER waveform morphology and normal or delayed latencies had a higher probability of hearing preservation in comparison to those with abnormal preoperative BAER morphology.

The auditory brainstem implant (ABI) restores some hearing sensations to patients deafened by bilateral acoustic tumors. Electrodes are stable for more than 10 years. In most cases nonauditory side effects can be avoided by judicious selection of the stimulating waveform and electrode configuration. Most perceptual measurements demonstrate that the ABI produces psychophysical and speech performance similar to that of single-channel cochlear implants. ABI patients receive suprasegmental information in speech and significant enhancement of speech understanding when the sound from the ABI is combined with lipreading.

Most patients with neurofibromatosis type 2 (NF2) are totally deaf after removal of their bilateral acoustic neuromas. Twenty-five patients with neurofibromatosis type 2 have been implanted with a brainstem electrode during surgery to remove an acoustic neuroma. The electrode is positioned in the lateral recess of the fourth ventricle, adjacent to the cochlear nuclei. The present electrode consists of three platinum plates mounted on a Dacron mesh backing, a design that has been demonstrated to be biocompatible and positionally stable in an animal model. Correct electrode placement depends on accurate identification of anatomic landmarks from the translabyrinthine surgical approach and also on intrasurgical electrophysiologic monitoring. Some tumors and their removal can result in significant distortion of the brainstem and surrounding structures. Even in the absence of identifiable anatomic landmarks, electrode location can be adjusted during surgical placement to find the location that maximizes the auditory evoked response and minimizes activation of other monitored cranial nerves. Stimulation of the electrodes produces auditory sensations in most patients, with results similar to those of single-channel cochlear implants. A coordinated multidisciplinary team is essential for successful application of an auditory brainstem implant.

The results of a U.K. study of 145 cases of type 2 neurofibromatosis has shown generally very poor operative results in terms of hearing and facial nerve preservation. Only 9 out of 118 vestibular schwannoma (acoustic neuroma) operations resulted in any clinically detectable hearing preservation and only 32 left the patient with good or normal (House grade I or II) ipsilateral facial nerve function. Although operation is still the definitive treatment of vestibular schwannoma (acoustic neuroma) and may be a lifesaving procedure, it appears that the evidence in favour of early operation is only valid when carried out in highly specialized centres. The special problems of NF2 cases who may go on to develop multiple spinal and cranial tumours making them wheelchair bound and blind as well as deaf warrants a careful experienced approach. Timing of operations may be critical for the enhancement of useful years of quality life. We therefore propose the setting up of a national NF2 register, with the management of cases at a few supraregional centres.

Unilateral vestibular schwannomas (VS) differ from those in patients with neurofibromatosis 2 (NF-2) clinically and by in situ appearance. To determine whether there are histopathologic differences, the presence of each of 16 histologic features was compared in first surgical resection specimens of 48 VS from 39 NF-2 patients and 293 unilateral VS. Antoni A and B areas, nuclear atypia, whorls, scarring, chronic inflammation, and sheets of macrophages were found equally in both groups. Vestibular schwannomas in NF-2 had more Verocay bodies, foci of high cellularity, and lobular growth patterns, the latter possibly correlating with in situ appearance. Ten NF-2 VS specimens had either meningiomas or microscopic meningeal cell proliferations removed with the VS from the same area, whereas none of the patients with a unilateral VS had these findings. Unilateral VS had more hyalinized and malformed vessels, recent and old thromboses and hemosiderin deposits. The differences could not be attributed to patient ages because there were similar differences between the VS in NF-2 and the unilateral VS of 40 patients age-matched to the NF-2 patients. There were more female patients in both groups, but gender did not influence the occurrence of any histologic features. There were nine additional patients with apparently unilateral VS but in whom the diagnosis of NF-2 was suggested by additional findings; six of the VS from these patients had lobular patterns.(ABSTRACT TRUNCATED AT 250 WORDS)

This chapter describes the basic principles of molecular genetics, particularly in relation to gene mapping and isolation (positional cloning). The application of this technology is illustrated by progress in elucidating the molecular basis of inherited tumour syndromes, including neurofibromatosis types 1 and 2 and von Hippel-Lindau disease, and molecular studies of tumourigenesis in malignant gliomas.

During a 4-year interval, 17 patients with bilateral acoustic tumors (vestibular schwannomas) underwent unilateral stereotactic radiosurgery using a multisource gamma unit; 2 patients underwent radiosurgery of both tumors in separate sessions. Eleven patients with unoperated contralateral tumors served as concurrent controls to compare the effects of radiosurgery with the natural history of acoustic tumors. After radiosurgery, the tumor control and regression rates were 89.5 and 21.1%, respectively (median neuroimaging follow-up, 1.4 years; range, 0.3-3.9). The tumor regression rate increased to 40% for patients evaluated at least 12 months after radiosurgery. In comparison to the unoperated contralateral tumors, stereotactic radiosurgery achieved tumor control, as assessed by the ultimate change in tumor size at follow-up (P, 0.012), the change in tumor size over time (P, 0.006), and tumor growth rates (P, 0.003). This study provided convincing evidence that tumor stabilization after radiosurgery (as assessed by neuroimaging) truly represented tumor control. The incidence of delayed facial neuropathy after radiosurgery compared favorably with the incidence reported after microsurgical removal. Some hearing was preserved in one-third of the patients who had preoperative hearing, including three patients who were contralaterally deaf. Stereotactic radiosurgery should be considered as a primary surgical modality for many patients with neurofibromatosis Type II.

Neurofibromatosis is a multifaceted disease that often results in tumors of the central nervous system. As our understanding of the molecular biology of the disease improves along with better neuroradiology imaging, surgical instrumentation, and adjunctive care, the management schemes for these patients are evolving. This article reviews what is known about neurofibromatosis, common management problems with respect to the central nervous system, and an approach to the handling of these issues.

A rare case of bilateral neurinoma of the acoustic nerve is described. The patient was a girl aged 19 years without external evidence of von Recklingshausen disease.

Hearing preservation was attempted in eight cases of acoustic neurinomas with good preoperative hearing. This was successful in 3 cases. Brain-stem auditory evoked potentials (BAEP0 were monitored in all cases, and compound nerve action potentials (CNAP) were recorded from the cochlear nerve in the last 3 cases. The BAEP was extremely sensitive to intraoperative manipulation. Intraoperative loss of wave V in BAEP was observed not only in all 5 cases with postoperative hearing loss, but also in 2 out of 3 cases with successful hearing preservation. CNAP correlated better with the hearing outcome than BAEP. In the cases where hearing was preserved, intact CNAP responses were demonstrated at the end of the operation. Conversely, deterioration of CNAP was seen in a case of postoperative hearing loss. CNAP was 10-15 times larger in amplitude than BAEP, so that the new responses were obtainable in shorter intervals. This capability of frequent examination seemed to increase the possibility of avoiding irreversible damage to the hearing by changing surgical tactics. The addition of CNAP monitoring is a good supplement to conventional BAEP monitoring in acoustic neurinoma surgery.

Stereotactic radiosurgery is performed under local anesthesia, and most patients can be discharged from the hospital within 24 hours of treatment. All patients in our series returned to their preoperative level of employment or function within 5 to 7 days of treatment, and this functional level was maintained over the period of follow-up. "Tumor control" was achieved in 96% of patients during an average follow-up of 1.7 years. Tumor shrinkage occurred in 45% of patients who had at least 1.5 years of follow-up. Useful hearing preservation rates were 50% at 6 months and 30% 1 year after treatment. New delayed facial or trigeminal neuropathy occurred in 34% and 32% of patients, respectively, with a median onset of 5 to 6 months after treatment. The vast majority of cranial neuropathies were partial at onset and tended to improve over time. Other complications included tumor growth (4%), communicating hydrocephalus (4%), and transient adjacent brain parenchymal changes best seen on T2-weighted MRI (9%). Stereotactic radiosurgery is an important alternative treatment for carefully selected patients with acoustic tumors. Indications for treatment include sufficient medical problems to pose excessive surgical risk, advanced age, the presence of bilateral acoustic tumors or contralateral deafness, recurrent tumor despite surgical resection, or refusal to undergo microsurgery. Radiosurgery is contraindicated in patients with symptomatic brain stem or cerebellar compression from a large acoustic tumor. Previous posterior fossa radiotherapy is a relative contraindication that must be considered on a patient to patient basis. Stereotactic radiosurgery should be viewed as an additional weapon in our arsenal for combating acoustic tumors rather than feared as a potential replacement for surgical excision. The strategic role of stereotactic radiosurgery in the overall treatment of patients with acoustic tumors will continue to be refined as longer-term, carefully assessed results become available.

With the aim of preserving hearing, 20 acoustic neurinomas in 17 patients with neurofibromatosis 2 were intentionally submitted to an incomplete (80%) tumour removal. In 12 cases this was an operation on the last hearing ear with total deafness of the contralateral ear. If an auditus existed in both ears the better hearing ear was selected for the primary intervention. Early audiological controls evidenced residual hearing in 19 of the 20 cases operated on by the enlarged middle fossa approach, which was utilized inspite of the tumour diameters being between 1 and 6 cm in the cerebello-pontine angle. The oncologic and functional follow-up over 1 to 7 years showed different patterns of slow progression of hearing loss and of persistent auditory function over 2 to 7 years. Facial nerve function was excellent in 16 of the 18 controlled cases. Continued CT or MRT imaging revealed no signaling in 2 cases, constant tumour sizes in 10 cases and slow progression in 3 cases. With regard to the importance of an auditory communication in the younger adult, the described treatment modality appears to be the first choice method.

Surgery for acoustic tumors has several priorities. First and foremost is the preservation of life with the total removal of the tumor; second is the preservation of the facial nerve; and last, when applicable, is the preservation of hearing. During the suboccipital (retrosigmoid) removal of a tumor, the surgeon unknowingly may leave tumor remnants leading to regrowth. We present five cases of recurrent acoustic tumors after a suboccipital removal. Inadequate drilling exposure of the internal auditory canal was the probable direct cause for tumor recurrence. A translabyrinthine removal is the best approach for total exposure of the entire internal auditory canal. The consequences of small tumor remnants will be discussed as well as their clinical relevance. Current radiological imaging and surgical techniques that avoid residual tumor will be presented.

Tumours located anterior to the cervicomedullary junction have been most commonly approached via one of two routes: anterior/transoral or posterolateral. Each of these surgical corridors can pose potential pitfalls. To circumvent these problems, a lateral suboccipital approach in conjunction with an upper cervical hemilaminectomy has been used. Selecting an appropriate surgical corridor between the lower cranial nerves (IX through XII), the vertebral artery, and the posterior inferior cerebellar artery has allowed satisfactory tumour removal. A three-dimensional picture of tumour location and relationship to surrounding neural and vascular structures is obtained preoperatively from computed tomography and magnetic resonance. Arteriography is essential to determine the origin, course, and relation of each vertebral to the tumour as well as the contribution of each vertebral to the basilar. In instances of abnormalities in the posterior circulation, evaluation of the carotid contribution to the basilar is crucial. The advantages of this approach are several. First, a direct view of the anterior surface of the lower brainstem und upper cervical cord is obtained. Second, surgery is undertaken in a sterile field in which the dura can be closed watertight. Third, neither mastoidectomy nor transposition of the vertebral artery is required. The major difficulty is the necessity to operate through narrow surgical corridors bounded by the lower cranial nerves, vertebral and posterior inferior cerebellar arteries, and the lower medulla and upper cervical cord. These structures provide the major obstacles to dissection as well as the primary causes of morbidity.

A case of pituitary adenoma associated with multiple neurinomas in the central nervous system was presented. A 52-year-old man was referred to us for surgical treatment of an intradural extramedullary cervical cord tumor. He had been operated on for a cauda equina tumor when he was 43 years old, and again for a glossopharyngeal neurinoma at 49 years of age. His brother expired in childhood, and had multiple subcutaneous nodules. The patient had been complaining of left leg pain, left shoulder pain, and hypesthesia of the right leg and foot. Examination showed 6th cervical nerve root sign. MRI revealed a well-circumscribed extramedullary tumor at the C5 level, and, in addition, incidentally showed an intra- and supra-sellar tumor which was isointensity on T1 weighted and high intensity on T2 weighted images. Myelography showed multiple extramedullary tumors in the lumbar region. Endocrinological study revealed an increased serum prolactin level (818.0ng/ml). The patient had neither café au lait spots nor subcutaneous nodules. A neurinoma of C6 root was totally removed and chromophobe pituitary adenoma was partially removed through a transsphenoidal approach. Neurofibromatosis is known to be associated with many kinds of tumors in the central nervous system. They are usually neurinomas, meningiomas or gliomas, and association of pituitary adenomas has been reported in only three cases, one of which being a prolactin secreting adenoma. Coexistence of multiple primary brain tumors has been also reported apart from phakomatosis. The most common combination is association of glioma and meningioma, and it is probably incidental coexistence due to their high frequency.(ABSTRACT TRUNCATED AT 250 WORDS)

The association of central nervous system neoplasms in neurofibromatosis is common and children are at particular risk. Recent advances in neurodiagnostic techniques allow for non-invasive detection of these tumors, and often these tumors are found in asymptomatic patients. Due to the diversity of neoplasms, varying grades of malignancy, variable growth patterns, and the occupancy of non-neoplastic hamartomatous lesions, the clinician often has difficulty determining which patient should have a diagnostic biopsy or resection, or if therapy should be started without pathologic confirmation. Following a review of the neuroradiology and more common intracranial tumors, recommendations regarding management are proposed.

Acoustic neuromas are benign schwannomas that arise from the vestibular portion of the eighth cranial nerve. Small tumors confined to the internal auditory canal may be removed via an extradural subtemporal approach. Tumors that involve the cerebellopontine angle require posterior fossa craniotomy utilizing either the suboccipital or translabyrinthine technique. The choice of surgical approach depends primarily on the size of the tumor, its location, and the status of hearing in the involved ear. Operative mortality is very low. The most common sources of morbidity are hearing loss and facial nerve dysfunction.