Suboccipital surgery for acoustic neurinomas: advantages and disadvantages

Acoustic cellular schwannoma invading the petrous bone: case report

Cellular schwannoma, a variant of benign schwannomas characterized by a high pseudosarcomatous cellularity, rarely involves the cranial nerves. In this report, we present the case of a 74-year-old woman with a cellular schwannoma of the VIIIth cranial nerve, which recurred from an ordinary schwannoma resected 9 years before. The tumor has been controlled for 35 months by a simple re-excision, indicating the benign nature of this tumor, although the tumor showed bone destruction and a high MiB-1 labeling ratio.

Hearing preservation in vestibular schwannoma surgery: what factors influence outcome?

The goals in the management of patients with vestibular schwannomas have changed drastically over the past few decades, with preservation of useful hearing representing the newest challenge. The true incidence of preserved useful hearing, however, has become clouded by a lack of uniformity in reporting results. The authors have analyzed 56 consecutive cases, in which directed attempts were made to preserve hearing on the involved side, to understand what factors play a major role in postoperative hearing preservation. Of the 56 cases reviewed, there were 46 patients who had "good" preoperative hearing (pure tone average < 50 dB; speech discrimination score > 50%). We found that, in this group of patients, if the tumor was less than 2 cm in diameter from pons to petrous, there was a 52% (16 of 31 patients) chance of preserving good hearing and if the tumor was 1 cm or less, the chances increased to 83%. Factors such as preoperative hearing status, tumor size and location, tumor consistency, and preoperative and intraoperative brainstem auditory evoked potentials are discussed in detail as they relate to postoperative outcome.

Change in facial nerve innervation following hypoglossal-facial anastomosis. An animal study

Hypoglossal-facial nerve anastomosis was carried out in 20 adult guinea pigs. Horseradish peroxidase (HRP) was applied to the buccal branch of the facial nerve at intervals of 2, 4 and 6 months after the anastomosis operation. HRP labeled neurons and the number of regenerated axons in the buccal branch were counted to determine postoperative nerve regeneration. The number of surviving neurons in the facial and hypoglossal nuclei was also counted to determine postoperative change of these nuclei. Following anastomosis, 97% of the hypoglossal neurons remained surviving, while the facial neurons underwent pronounced degeneration of 65% survival ratio at 2 months and 37% at 6 months after the anastomosis operation. In 80% of the animals, a new nerve bundle regenerated from the proximal stump of the facial nerve to the anastomotic trunk. A linear increase of HRP-labeled neurons in the facial and hypoglossal nuclei paralleled the increase of the axons in the buccal branch. The HRP-labeled neurons in the facial nucleus were demonstrated to have direct connection with the newly formed bundle and the facial mimetic muscles were dually innervated by both the hypoglossal and facial nerves. Although the present study design might not fully represent the clinical situation, possible advantages of hypoglossal-facial nerve anastomosis are discussed from the view of nerve regeneration.

Facial nerve outcome after acoustic neuroma surgery

Factors influencing facial nerve preservation and function in acoustic neuroma surgery were studied in 108 cases. Anatomic preservation of the nerve was inversely related to tumor size and improved as the series progressed. When the nerve was saved, normal postoperative function was inversely related to tumor size and was more common if the cochlear nerve was also saved. Most intact nerves eventually recovered some function, but late function was seldom completely normal unless there was some early recovery. The results demonstrate the importance of tumor size, operator experience, and ease of dissection on facial nerve outcome.

Ultrasonographic and electrophysiological adjuncts to surgery within the brain stem: technical note

The surgical approach to intrinsic lesions within the brain stem is undertaken by the surgeon knowing the potential for significant operative morbidity. We report the use of real-time intraoperative ultrasound and electrophysiological mapping techniques to aid in the localization and resection of an intrinsic brain-stem tumor in a child. These techniques permitted an aggressive surgical approach without encountering adverse postoperative neurological sequelae.

Facial nerve monitoring by monopolar low constant current stimulation during acoustic neurinoma surgery

Electrophysiological characteristics of monopolar low constant current stimulation, and evoked facial muscle responses to such stimulation, were evaluated in 34 cases of acoustic neurinoma. Our study, using stimulus parameters of 0.1-ms-duration pulse wave with 0.5-0.6 mA intensity, revealed that extent of spreading current depends on the current intensity, being about 1 mm from the electrode with 0.5-0.6 mA, and insulation of the electrode prevented the current from spreading through the cerebrospinal fluid, giving a reliable amount of current to the tissue. Evoked facial muscle responses to facial nerve stimulation in the internal auditory meatus and over the pons were analyzed and revealed the following: (1) The responses to stimulation in the internal auditory meatus showed no amplitude attenuation throughout the operation. (2) The responses to stimulation over the pons gradually decreased in amplitude as tumor dissection from the nerve proceeded, especially in large tumors. (3) Anatomical continuity of the nerve was obtained in 100% of small, 91.7% of medium, and 88.2% of large tumors. Our data show that monopolar low constant current stimulation is effective in obtaining the precise anatomical orientation of the facial nerve during tumor removal.

The impact of continuous electrophysiological monitoring on preservation of the facial nerve during acoustic tumour surgery

Continuous electromyographic (EMG) activity and responses to electrical stimulation of the facial nerve were monitored intraoperatively in 35 patients undergoing primary removal of acoustic neuroma. The rate of anatomical and immediate functional preservation of the facial nerve of these patients was compared with a matched population where a facial nerve stimulator and monitoring of facial muscle contraction by the anaesthetist only was employed. Overall, 94% (n = 33) of facial nerves were preserved anatomically in patients with continuous EMG monitoring, compared with 64% (n = 89) of patients (n = 139) without continuous monitoring. Amongst the 33 cases with anatomical facial nerve preservation, 64% (n = 21) had immediate functional preservation. Immediate functional preservation was only achieved in 39% (n = 35) of anatomically preserved facial nerves (n = 89) where conventional monitoring was used.

Efficacy of irradiation for incompletely excised acoustic neurilemomas

The records of 124 patients treated for acoustic neurilemoma at the University of California, San Francisco, from 1945 through 1983 were reviewed. Patients were classified by the extent of surgical resection: total, nearly total (90% to 99% resection), subtotal (less than 90% resection), or biopsy. Thirty-one patients received irradiation as part of their primary treatment. Total resection of tumor, without irradiation, was associated with a 3% chance of local recurrence. One of 15 patients who had nearly total resection of their tumor and did not receive postoperative irradiation suffered a recurrence, compared with neither of the two patients who received postoperative irradiation (greater than 45 Gy) following nearly total resection. Postoperative irradiation (greater than 45 Gy) decreased the recurrence rate after subtotal resection from 46% (six of 13 cases without irradiation) to 6% (one of 17 cases: p = 0.01). All three patients treated by biopsy alone received postoperative irradiation (greater than 45 Gy), and none had a recurrence. Six patients were treated with preoperative irradiation because of excessive tumor vascularity; four are without evidence of disease 12 to 23 years later. Only three of seven patients treated with irradiation for tumor recurrence after surgical resection survived. It is concluded that postoperative irradiation significantly decreased the chance for local tumor progression following subtotal resection of acoustic neurilemoma, and that postoperative irradiation may be effective therapy following treatment by biopsy. Patients with total or nearly total resection appeared not to benefit from postoperative irradiation.

Total one-stage suboccipital microsurgical removal of acoustic neuromas of all sizes: with emphasis on arachnoid planes and on saving the facial nerve

Clinical suspicion is essential for early diagnosis of acoustic neuroma. No absolutely characteristic pattern of hearing loss occurs, and atypical presentations are the rule. The diagnosis of acoustic neuroma is possible by tests that can be performed on an outpatient basis. A hearing loss for high tones with impaired speech discrimination is frequently seen. Testing of the acoustic reflexes and particularly the brain stem auditory-evoked responses (BAER) are becoming the most reliable methods of defining hearing loss in patients suspected of having an acoustic neuroma. High-resolution, thin-sectioning, overlapping-cut CT scanning including CT pneumography when necessary and polytomography of the internal auditory meatus are the mainstays of radiologic evaluation. Complete removal of the tumor at one operation is usually possible by the suboccipital retromastoid route with preservation or restoration of normal brain stem function and preservation of facial nerve function. Preservation of hearing has occasionally been accomplished, and the potential occasionally exists for restoration of hearing in patients with favorable smaller tumors, which have not acquired extensive arterial supply in common with the cochlea. The two factors that most influence results are early diagnosis and gentleness of surgical manipulation of the tissues that is made possible by magnification and illumination with the operating microscope.

The suboccipital approach to removal of acoustic neuromas

This article reviews the author's technique for removing acoustic neuromas by the suboccipital approach. Also discussed are various considerations regarding the selection and use of instruments for this operation. The anatomy of the internal acoustic meatus and the principles involved in facial- and cochlear-nerve preservation are described. A guide is provided for stepwise dissection of the internal acoustic meatus in the laboratory.

Preservation of hearing in tumors of the internal auditory canal and cerebellopontine angle

One hundred thirty-nine tumor removals are reviewed with special interest in ten attempts to save hearing. Three patients with bilateral tumors had some hearing preserved. One of these individuals had a 1 cm tumor removed and his postoperative SRT and discrimination scores were the same as his preoperative ones. Overall, the authors were able to maintain some hearing in six out of ten attempts. While there is no question that patients with bilateral tumors benefit from residual hearing, this is not always true in unilateral cases. The suboccipital and middle fossa procedures are discussed as well as the relative merits of each approach in the preservation of hearing. The total series (139 tumors) is discussed in detail regarding results and complications.

Facial nerve function after suboccipital removal of acoustic neurinoma

The recovery of facial nerve function after suboccipital removal of 91 acoustic neurinomas is presented. The results after anatomical preservation of the nerve (60 cases), direct anastomosis of the nerve (7 cases), nerve grafting (16 cases), and facial hypoglossal anastomosis (8 cases) are presented after a follow-up period of 31.2 months. A simplified classification was used to describe motor function. The results are compared to those in the literature.