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Delayed facial palsy occurs after approximately 15% of acoustic neuroma resections. Whereas in most cases facial nerve function recovers satisfactorily, in about 12% of cases delayed facial palsy may have a poor functional recovery. The fate of facial nerve function was studied in 55 consecutive translabyrinthine acoustic neuroma resections, 23 of whom underwent meatal facial nerve decompression (MFND) at the time of tumor resection. The facial nerve results also were reviewed in 19 middle cranial fossa resections, of whom 14 underwent MFND. There was a bimodal distribution of the delayed palsies, with one group having the onset of palsy within hours to 2 days after surgery and the second group having onset of palsy up to 17 days after surgery. The poorest recoveries were seen in the first group. Although the effect was not statistically significant due to the small sample size, the chance of facial weakness in patients who underwent MFND after translabyrinthine surgery was about 40% less than in those who did not undergo decompression. The apparent protective effect of MFND was increased when the confounding factors of tumor size and degree of resection were taken into account, although the effect was not statistically significant. The duration of palsy was shorter and ultimate recovery better among the patients who underwent facial nerve decompression than in those who did not. Of the translabyrinthine patients who underwent MFND, 100% had House-Brackmann grade I-II function at 2 years, whereas 87% of patients who did not have MFND had grade I-II function and 13% had grade III-IV function. Without MFND, 57% of translabyrinthine patients whose onset of facial palsy was within 2 days of surgery had grade III-IV facial nerve function.

Seventy-three procedures involving 70 acoustic tumors were carried out over 3 years. The majority of tumors (65) were removed by the translabyrinthine approach. Tumor size ranged from 0.5 through 5.0 cm. All patients underwent intraoperative facial nerve monitoring: 22 patients developed immediate facial palsy (House-Brackmann grades II-VI); 11 patients recovered completely; 11 patients (15.7%) had persistent paralysis. The incidence of long-term, poor outcome (H-B grade IV-VI) was 5.7 percent. The overall incidence of facial palsy was not found to be related to tumor size; however, facial paralysis associated with large tumors exhibited a poorer House-Brackmann grade compared to small and medium lesions. The use of intraoperative facial monitoring has enhanced the surgeon's ability to preserve facial nerve function by reducing the overall incidence of postoperative facial paralysis.

Ten patients with surgically confirmed residual cerebellopontine angle neuromas, imaged by both computerized tomography (CT) with iodine contrast and magnetic resonance (MR) with and without gadolinium enhancement, are reviewed to identify the strengths and limitations of MR as compared with CT imaging. MR imaging offers superior anatomic resolution in multiple imaging planes without ionizing radiation, but it is expensive and has adverse effects on some patients. CT imaging offers good anatomic resolution, but in only one or two planes. CT is both less expensive and generally well tolerated, but allergy to the iodine contrast is not uncommon. The cases presented demonstrate the adequacy of CT imaging of residual tumor. However, in some cases MR imaging provided important additional detail. MR imaging also demonstrated postoperative changes within the brain stem and cerebellum. In our experience, CT imaging remains a satisfactory, unambiguous approach to the assessment of known postoperative residual cerebellopontine angle neuromas. MR imaging provides superior resolution, however, and should be used when better definition of tumor detail is needed for management decisions or when multiple follow-up scans are anticipated, so that the exposure to ionizing radiation is limited. MR is also useful to investigate postoperative neurologic dysfunction. Postoperative changes and residual tumors are more difficult to interpret on MR than on CT. Guidelines are proposed to help distinguish residual tumor from postoperative changes and scarring.

The objective of surgical management of acoustic tumors is to remove them entirely and preserve facial nerve function and hearing when possible. A dilemma arises when it is not possible to remove the entire tumor without incurring additional neurologic deficits. Twenty patients who underwent intentional incomplete surgical removal of an acoustic neuroma to avoid further neurologic deficit were retrospectively reviewed. They were divided into a subtotal group (resection of less than 95% of tumor) and a near-total group (resection of 95% or more of tumor) and were followed yearly with either computed tomography or magnetic resonance imaging. The subtotal group was planned and consisted of elderly patients (mean age, 68.5 years) with large tumors (mean, 3.1 cm). The near-total group consisted of younger patients (mean age, 45.8 years) and smaller tumors (mean, 2.3 cm). The mean length of followup for all patients was 5.0 years. Ninety percent of patients had House grade I or II facial function post-operatively. Radiologically detectable tumor regrowth occurred in only one patient, who was in the subtotal resection group. Near-total resection of acoustic tumor was not associated with radiologic evidence of regrowth of tumor for the period of observation. Within the limits of the follow-up period of this study, subtotal resection of acoustic neuroma in elderly patients was not associated with clinically significant recurrence in most patients and produced highly satisfactory rates of facial preservation with low surgical morbidity.

Wound infection, cerebrospinal fluid leak, and meningitis are serious potential complications of neurotologic procedures that transgress the posterior cranial fossa dura. A study of 236 patients was made to determine the effect of perioperative intravenous antibiotics and topical bacitracin irrigation on the incidence of these complications. Of the 236 patients, 170 (72%) underwent translabyrinthine resection of acoustic tumors, while 66 (28%) underwent retrolabyrinthine vestibular nerve section. Patients were divided into four groups: those who received no antibiotics, those who received perioperative intravenous antibiotics only, those who received topical bacitracin irrigation only, and those who received a combination of perioperative intravenous antibiotics and topical bacitracin irrigation. There were no untoward effects of either perioperative intravenous antibiotics or topical bacitracin. The results indicate that bacitracin irrigation reduced the incidence of wound infection from 9% to 2% (p less than 0.05); of cerebrospinal fluid leak from 12% to 5% (p less than 0.04); and of all targeted complications combined from 22% to 9% (p less than 0.006). Furthermore, the topical bacitracin irrigation only group showed a statistically significant reduction in wound infections compared to the perioperative intravenous antibiotic only group (p less than 0.02). The incidence of meningitis was statistically unaffected by any of our treatment protocols.

Preservation of facial nerve function during acoustic tumor resection is an important goal. Patients with acoustic tumors who present with facial weakness may be at increased risk of postoperative facial paralysis. Subclinical tumor involvement of the facial nerve may be more frequent than is commonly recognized. A preliminary study was undertaken to assess the incidence of subclinical involvement of the facial nerve and to discern if such involvement had prognostic implications. Preoperative facial electroneurography (ENoG) was performed in thirteen patients undergoing surgical resection of acoustic tumors. Three of thirteen patients demonstrated preoperative facial weakness and ENoG was abnormal in all three of these patients. Of the ten patients with normal facial function preoperatively, eight revealed amplitude reduction on ENoG testing. Further study is required to discern the prognostic value of preoperative ENoG abnormalities.

Intraoperative facial nerve monitoring provides a potentially useful adjunct to recent surgical advances in neurotology and neurosurgery. These measures further aid the surgeon in preserving facial nerve function by enhancing visual identification with electrical monitoring of mechanically evoked facial muscle activation. Facial nerve monitoring in neurotologic surgery may achieve the following goals: (1) early recognition of surgical trauma to the facial nerve, with immediate feedback made available to the surgeon through monitoring of mechanical activation; (2) assistance in distinguishing the facial nerve from regional cranial nerves and from adjacent soft tissue and tumor with selective electrical stimulation; (3) facilitation of tumor excision by electrical mapping of portions of tumor that are remote from the facial nerve; (4) confirmation of nerve stimulability at the completion of surgery; and (5) identification of the site and degree of neural dysfunction in patients undergoing nerve exploration for suspected facial nerve neoplasm or undergoing decompression in acute facial palsy. This paper provides an overview of intraoperative facial nerve monitoring principles and methodology and reports a recent clinical investigation that demonstrates the utility of facial nerve monitoring in translabyrinthine acoustic neuroma surgery.

The patient with an acoustic neuroma may present to the otologist with a variety of clinical features. Classically these include a retrocochlear pattern of sensorineural hearing loss, reduced vestibular response on caloric testing and radiological asymmetry of the internal auditory canals (IAC). The absence of any or all of these features, however, does not exclude the presence of tumour. Five cases are presented to illustrate the potential for diagnostic delay unless a routine battery of investigations is undertaken in patients with neuro-otological disorders. All patterns of subjective audiometry are encountered, auditory brain stem response testing may be unreliable where hearing loss is profound, vestibular testing is normal in half of small tumours and the intracanalicular tumour may be radiologically undetectable unless IAC meatography is employed.

Earlier diagnosis of acoustic tumors promises to increase our opportunity to identify patients with serviceable hearing. Critical to a posterior fossa transmeatal approach for acoustic tumor resection is preservation of the underlying labyrinth. Although the labyrinth has been recognized as a limiting factor in exposure of tumor in the internal auditory canal, few reports have detailed the microscopic surgical anatomy posterior to the internal auditory canal. An anatomic study was undertaken to determine consistent relationships between critical structures within the temporal bone relevant to hearing preservation surgery. The results of this study indicate that, whereas topographic landmarks are helpful for orientation, the more consistent relationship of the labyrinth to the vestibular aqueduct and singular canal allows a more accurate localization of the underlying labyrinth. Although the vestibule frequently prevents direct visualization of the transverse crest, a dissection based upon the microsurgical anatomy will maximize visualization of the lateral fundus while preserving the integrity of the labyrinth.

Tumors of the temporal bone and cerebellopontine angle may be associated with subclinical facial nerve degeneration, despite clinically normal facial function. To determine if preoperative neurophysiologic testing might predict postoperative facial function after tumor surgery, preoperative facial electroneurography (ENoG) was performed in 82 patients with confirmed tumors of the temporal bone and cerebellopontine angle. In patients with acoustic neuroma, preoperative ENoG amplitude reduction varied directly with tumor size. In addition, a statistically significant association between impaired postoperative facial function and acoustic neuroma size greater than 2.5 cm was found. However, preoperative ENoG amplitude reduction did not accurately predict postoperative facial function. These findings suggest that factors, such as the type and size of tumor, the microanatomic relationship between the facial nerve and the neoplasm, and/or desynchronization of the evoked motor-unit volley, may effect results obtained with ENoG in this setting.

Despite the widely held notion that acoustic neuroma is a disease of the middle and late years of life, this neoplasm frequently begins in young adults. It has been reported as occurring in a patient as young as seven years of age. Often, patients in their 20s or 30s may have minimal symptoms despite sizable tumors. Constant alertness for such lesions is essential for early diagnosis and optimal prognosis.

Lesions of the temporal bone and cerebellopontine angle present a diagnostic challenge because of the complex anatomy, multiplicity of lesions, and difficulty in imaging the dense bone of this area. Magnetic resonance imaging, a new, nonionizing imaging modality, dependent on monitoring a radiofrequency signal emitted by excited nuclei in an external magnetic field, has shown promise in imaging of the temporal bone and posterior fossa.

Auditory brainstem response testing has been a major breakthrough in audiologic screening for acoustic neuroma because of its high degree of sensitivity. Although it is not uncommon for other cerebellopontine angle masses to present with normal ABR findings, reports of eighth nerve tumors with false-negative auditory brainstem response tests are quite rare. A series of 120 acoustic neuromas resected at the University of Michigan was reviewed and revealed two such patients. These two patients presented with asymmetric sensorineural hearing loss and unilateral tinnitus and were found to have completely normal auditory brainstem response. The diagnosis of acoustic neuroma would have been delayed if a comprehensive evaluation had not been pursued.