Frequency specific hearing improvement in microvascular decompression of the cochlear nerve

BACKGROUND

Microvascular compressions of the cochlear nerve can lead to hearing loss. Due to the tonotopic organization of the cochlear nerve any focal compression of the cochlear nerve will result in a frequency specific hearing loss. Decompressing the cochlear nerve could result in a frequency specific hearing improvement, without improving overall hearing.

METHOD

Thirty one patients underwent microvascular decompression operations of the vestibulocochlear nerve for vertigo or tinnitus. Preoperative audiograms were substracted from postoperative audiograms obtained 2 years after microvascular decompression. The frequencies of maximal hearing improvement postoperatively were determined.

FINDINGS

Of the 31 patients studied, 19 had improvements of 5 dB or more at one or more frequencies postoperatively, and 15 patients had improvements of 10 dB or more. Three patients had improvements of 25 dB or more postoperatively. The postoperative hearing improvement was frequency-specific and related to the anatomical location of the vascular contact on the auditory nerve. The improvement of hearing becomes diluted when the difference between pre- and postoperative hearing thresholds are averaged over all audiometric frequencies. We therefore present results for each frequency that was tested.

CONCLUSIONS

Microvascular decompression of the cochlear nerve can improve hearing in selected patients. The improvement seems too small to justify decompressive surgery for the sole purpose of hearing improvement, but it could be considered if associated short vertigo spells, ipsilateral tinnitus, otalgia and cryptogenic hemifacial spasm are present. Decompression should be performed early, before BAEP changes become noticeable. 3D-MRI could become a valuable tool for selecting good surgical candidates.

[Auditory neuropathy--new disease]

Auditory neuropathy, a disorder of neural synchrony, is a retrocochlear hearing disorder identified by absence of auditory brainstem responses (ABR) and presence of evoked acoustic otoemissions (EOA). Registration of emissions shows normal function of external cilliary cells. Patients with auditory neuropathy have difficulties to understand speech especially in presence of beckground noise. Normal conversation requires the support of orofacial reading. The authors presents electrophysiological and behavioral tests useful in diagnostic process. An option in treatment of auditory neuropathy is cochlear implantation. Such treatment is indicated when conventional hearing aids doe not help to improve speech understanding.

Cochlear implantation in an adult patient with auditory neuropathy

We present a case report of effective cochlear implantation for an adult patient with auditory neuropathy. A 34-year-old man developed bilateral hearing loss at approximately 10 years of age. His speech discrimination score was very severe despite only moderate sensorineural hearing loss. Absence of auditory brainstem responses (ABR) and preservation of distortion product otoacoustic emissions (DPOAE) were confirmed by our audiological examinations. After cochlear implantation, good responses for electrically evoked compound action potential (EAP) and electrically evoked ABR (EABR) were observed. Postoperatively, his audiological performance was significantly improved. We conclude that cochlear implantation can be a valid option for patients with auditory neuropathy.

Vascular malformation (so-called hemangioma) of Scarpa's ganglion

Vascular malformations of the cerebello-pontine angle (CPA) arising from the capillary plexus surrounding Scarpa's ganglion are rare tumors. We report a case of so-called "hemangioma" of the CPA which was operated on via a trans-labyrinthine approach based on a preoperative diagnosis of vestibular schwannoma. Although there are some differences between these tumors in terms of the clinical, biological and especially MRI findings, surgery is usually performed based on an assumption of vestibular schwannoma. Surgery is the treatment of choice for these lesions as early intervention ensures better postoperative facial function. It is important to make the differential diagnosis if conservative management of vestibular schwannoma is adopted.

Galvanic-induced body sway in vestibular schwannoma patients: evidence for stimulation of the central vestibular system

OBJECTIVE

To investigate the various possible sites of excitation by galvanic stimulation by comparing the galvanic-induced body sway (GBS) in vestibular schwannoma (VS) patients with that in healthy subjects.

MATERIAL AND METHODS

This was a prospective experimental study conducted in a tertiary referral centre. In a previous study we developed a standardized procedure for reproducible quantification of GBS using a monaural continuous 1-cosinusoidal stimulus (0.5 Hz; 2 mA). In this study, 23 VS patients were tested before and 12 VS patients were also tested after surgical intervention (extirpation of tumour with concomitant vestibular neurectomy) and the results were compared with those obtained in 47 healthy subjects.

RESULTS

There were no significant differences in mean total GBS gain between VS patients and healthy subjects (p>0.05) before surgical intervention. After vestibular neurectomy a significant difference in the mean total GBS gain was observed, but GBS was still present after surgery.

CONCLUSION

These results prove that galvanic vestibular stimulation excites the central vestibular system even when conduction via the vestibular nerve is hampered.

Epithelioid schwannoma of the vestibular nerve

Epithelioid schwannomas are rarely encountered intracranially, with only four cases involving the eighth nerve reported in the literature. Histological behaviour ranging from benign to aggressive has been described. We report a 45-year-old woman who presented with right-sided tinnitus and hearing impairment. Magnetic resonance imaging revealed a tumour in the right cerebellopontine angle with intracanalicular extension. The patient underwent retromastoid craniectomy with near-total tumour excision. Microscopical examination confirmed the diagnosis of epithelioid schwannoma of the vestibular nerve. Intraoperative findings of sharp circumscription, bland histological appearance, low proliferative activity, coupled with the indolent clinical course, point to the quiescent nature of the lesion in this case.

Cochlear implants: indications in groups of patients with borderline indications. A review

Cochlear implants (CI) represent the current treatment for patients affected by profound sensorineural hearing loss (SNHL). Initially only deaf adult patients were considered to be candidates for a CI; however, the development of technology and matured experience have expanded the indications for cochlear implantation. Today, CIs are implanted in adults and children and broader indications are followed. There are, however, a number of patients who do not completely fulfill the current indications and who are potential candidates for CI. The duration of deafness and residual hearing represent prognostic indicators for CI performance; however, the candidacy of children with residual hearing and prelingually deafened adults are still under debate. Anatomical variants such as cochlear ossification, cochlear malformation and chronic otitis media represented and still represent for some surgeons a contraindication to CI. The otological experience of CI surgeons and the advent of auditory brainstem implants have changed the approach to these patients, who may still benefit from hearing rehabilitation. This paper briefly analyses and reviews the results obtained in these groups of patients, who were not, at least initially, considered to be candidates for cochlear implantation.

Internal auditory canal metastasis

This report deals with 3 cases of internal auditory canal metastasis, an extremely rare lesion, few cases having been reported in the international literature. Since pre-operative diagnosis is fundamental in the planning of a correct therapeutic strategy, it is important that the neurotologist be aware of the possibility of their occurrence in this particular area. Metastasis can occur unilaterally as well as bilaterally; the latter being the case in 1 of the patients described herein. Correct pre-operative diagnosis is particularly difficult in patients in whom the primary tumour has not been detected at the time of identification of the lesion in the internal auditory canal. The only characteristic, specific of metastasis, is the presence of multifocal cerebral lesions. However, these were detected in only 1 of the present cases. On the contrary, in cases of a single metastasis, both magnetic resonance imaging and computed tomography usually fail to show any distinctive feature when compared to the most common tumours of the internal auditory canal (vestibular schwannomas and meningiomas). Bilateral metastases can also be misdiagnosed as neurofibromatosis type 2. Clinical data that should alert the clinician are: rapidly progressive sensorineural hearing loss, followed by onset of progressive facial nerve weakness. Radiotherapy and/or chemotherapy are the two main treatment modalities, while surgical removal is reserved for selected cases of a single metastasis. Albeit, due to the paucity of specific radiological and clinical characteristics, surgical removal is often necessary to reach the correct diagnosis, as occurred in 2 of the present patients.

Endoscope-assisted Microsurgery for Microvascular Compression Syndromes

OBJECTIVE

To discuss the results of endoscope-assisted surgery in microvascular decompression (MVD) of Cranial Nerves (CNs) V, VII, and VIII.

METHODS

Neuroendoscopy was used as an adjunct to the surgical microscope in the MVD of the trigeminal (17 patients), facial (10 patients), and vestibulocochlear (1 patient) nerves in a series of 28 consecutive patients. After a standard microsurgical approach to CNs V, VII, and VIII, the endoscope was used to inspect all aspects of neural anatomy, to assess vascular compression, and to check the results of the decompression. Endoscope use was graded in four categories: Grade I, used but no definite role; Grade II, visualization assisted; Grade III, procedure assisted; and Grade IV, primary role. The usefulness of the endoscope was evaluated in each case.

RESULTS

The endoscope was useful in visualizing the anatomy in all cases. It was especially useful in establishing trigeminal vein compression of CN V in Meckel's cave; observing multiple sources of vascular compression; ensuring adequate decompression after cauterization of vein, insertion of the Teflon felt, or a pexy procedure; and permitting observation of the compression of CN VII at the root exit zone by small arteries and veins. In six patients with trigeminal neuralgia, the trigeminal vein was cauterized and divided by using endoscopic vision only because the venous compression was not completely visualized with the microscope. During a follow-up period of 6 to 52 months (mean, 29 mo; median, 40 mo), all patients were asymptomatic and receiving no medication.

CONCLUSION

The endoscope is a useful adjunct to MVD in the treatment of trigeminal neuralgia, hemifacial spasm, and disabling positional vertigo or tinnitus.

[Assessment of the state of water sectors in neurosurgical profile patients in the pre-, intra- and postoperative periods]

The state of water sectors has been analyzed at the stages of preparation to and performing anesthesia as well as in the early postoperative period in neurosurgical patients in connection with planned surgical procedures (37 cases). The impedance method of control of the hydration degree before operation allowed to find out a risk group--hypohydrated patients. In most cases the detected disturbances of the water-electrolytic balance could not be diagnosed clinically. Despite a relative stability of traditionally analyzed indices of circulation during anesthesia, the reactions of central hemodynamics were more pronounced than could be considered undesirable. The analysis performed makes a foundation for optimization of infusion and cardiotropic therapy both during anesthesiological maintenance of neurosurgical procedures and at the postoperative period.

[Are we sectioning the cochlear efferent system during vestibular neurotomy?]

INTRODUCTION

In addition to sensory neurons which transmit information from the inner ear to the brain, there is a system of efferent feedback fibers, called the olivocochlear system, carrying signals from the brain to the ear. Over the past half-century, the efferent system has been extensively studied in animals and results provided theories as to the functional significance of these efferents: to improve signal-to-noise ratio in the auditory periphery, to mediate selective attention, and to protect the inner ear from acoustic overexposure. The results of several studies conducted in man rely on the study of patients who have undergone a vestibular neurectomy. Indeed, anatomical data show that olivocochlear efferents could travel along or inside the vestibular part of the auditory nerve before reaching the organ of Corti. Therefore, these patients may be considered as an experimental model of unilaterally de-efferented subjects. However, to date, none has reported the existence of olivocohlear efferents in the vestibular section following neurectomy.

MATERIALS AND RESULTS

In this study, we present the histological results from 18 vestibular sections and show the absence of olivocochlear efferents.

CONCLUSION

These results provide a reason to reconsider the results of previous experiments conducted in similar patients and ask for further studies on the olivocochlear efferents pathways.

Cochlear implantation in patients with auditory neuropathy of varied etiologies

OBJECTIVES/HYPOTHESIS

Auditory neuropathy is a relatively recently described pattern of hearing loss characterized by preservation of outer hair cell function despite absent brainstem auditory evoked responses. Intact outer hair cell function is demonstrated by the presence of otoacoustic emissions and/or a measurable cochlear microphonic on electrocochleography, whereas no synchronous neural activity (absent action potentials) is seen on acoustically evoked brainstem auditory evoked response testing. The study reviews the authors' experience with six patients diagnosed with auditory neuropathy, four of whom have undergone cochlear implantation.

MATERIALS AND METHODS

A retrospective review of all medical and audiological charts at the University of Virginia Hospitals (Charlottesville, VA) was performed to identify patients who have undergone cochlear implantation or have been diagnosed with auditory neuropathy, or both.

RESULTS

Six patients with hearing loss attributable to auditory neuropathy were identified, four of whom have undergone cochlear implantation. Causes varied, including congenital, infectious, and idiopathic origins. Adults demonstrated subjective auditory perception on promontory stimulation, whereas no repeatable brainstem auditory evoked response waveforms could be demonstrated on pediatric promontory stimulation testing. Patients with implants demonstrated implant-evoked brainstem auditory evoked responses and improved audiological performance.

CONCLUSIONS

The six cases presented in the study represent varied causes and, probably, varied sites of lesions of auditory neuropathy. Promontory stimulation has been valuable, particularly in adults. Cochlear implantation allows the opportunity to provide a supraphysiological electrical stimulation to the auditory nerve, with the hope of reintroducing synchronous neural activity. Greater confidence and enthusiasm for cochlear implantation in appropriately selected patients with auditory neuropathy are gained through experience with such diverse cases.

Aggressive vestibular schwannomas with postoperative rapid growth: clinicopathological analysis of 15 cases

OBJECTIVE

Vestibular schwannomas (VSs) are known to be relatively slow-growing tumors. Some VSs, however, rapidly regrow or recur after surgical resection. Our objective was to investigate the clinicopathological characteristics of these tumors and to elucidate factors that can predict rapid regrowth or recurrence after surgical resection.

METHODS

Between 1978 and 2000, 29 patients with VS underwent reoperation for regrowth or recurrence at the Department of Neurosurgery in Seoul National University Hospital. Among these patients, 15 experienced rapid VS regrowth or recurrence (annual growth rate, >15 mm/yr). The clinical, radiological, operative, and pathological findings were reviewed. For a comparison of the morphology and proliferative activity, 15 cases of VS were randomly selected as a control group from among the consecutive operative cases with tumor size larger than 4 cm treated between 1991 and 1999. Pathological parameters consisting of cellularity, pleomorphism, mitosis, necrosis, invasion to adjacent tissue, and microvascular proliferation were analyzed. Proliferative indices (e.g., Ki-67 index) also were evaluated. Statistical analyses were performed using Fisher's exact test and the analysis of variance test.

RESULTS

The differences in clinical features between the aggressive VS group and the control VS group were nonspecific. The mean ages at diagnosis were 40.6 years (range, 21-63 yr) and 49.7 years (range, 35-67 yr) (P = 0.438), and the male-to-female ratios were 7:7 and 5:10 (P = 0.462), respectively. The clinical symptoms and signs were similar between the two groups. Radiologically, aggressive tumors at initial presentation had more lobulating contours than those in the control group (7 of 13 cases versus 3 of 15 cases; P = 0.001). In pathological findings, cellularity and pleomorphism were significantly higher than those in the control group (P = 0.001). However, mitosis, necrosis, invasion to adjacent tissue, and microvascular proliferation were not different between the two groups. The proliferative index (Ki-67 index) was higher in the aggressive group than in the control group (2.28 [range, 0.1-8.6] versus 0.59 [range, 0-1.5]; P = 0.034).

CONCLUSION

VSs presenting with lobulating contour, high proliferative index (Ki-67 index), and high cellularity or pleomorphism require frequent radiological investigation during follow-up to facilitate early detection of regrowth or recurrence.

Outcome of cochlear implantation in pediatric auditory neuropathy

OBJECTIVE

Auditory neuropathy, characterized by absence or abnormality of auditory brainstem responses and normal otoacoustic emissions, is often associated with particularly poor response to amplification. Outcome data from four such pediatric patients who received cochlear implants are discussed.

STUDY DESIGN

Four patients from the Carolina Children's Communicative Disorders Program were identified as having received a diagnosis of auditory neuropathy before implantation with a Clarion cochlear implant. Speech data collected after implantation were compared with data from control pediatric implant patients, matched for age at implantation and duration of implant use. Electrically evoked auditory brainstem response data and electrically evoked acoustic reflex data were also obtained.

METHODS

Routine clinical procedures were used to obtain speech outcome data. A 75-micros biphasic 21.1-Hz pulse train served as the eliciting stimulus for both evoked auditory brainstem responses and reflex measures, which were obtained contralateral to the implant.

RESULTS

Speech data were comparable with those obtained from the general population of pediatric patients receiving cochlear implants at this center. Identifiable evoked auditory brainstem response data were obtained in all subjects on at least two of the three electrodes tested, and variability was comparable with that observed in other children with implants. A robust electrically evoked acoustic reflex with no decay was observed at estimated M-level in all children.

CONCLUSION

The data gathered to date suggest that the outcome of cochlear implantation in these four patients is not significantly different from that in other pediatric implant patients. Physiologic data suggest that the implant was able to overcome the desynchronization hypothesized to underlie auditory neuropathy.

Neuromuscular hamartoma of the cochlear nerve: a rare occurrence in the internal auditory meatus

The authors present a case of neuromuscular hamartoma of the cochlear nerve, an unusual occurrence in the internal auditory meatus (IAM). A review of the literature shows no previous report of neuromuscular hamartoma of the cochlear nerve. This tumour was clinically and radiologically difficult to distinguish from acoustic neuroma. It is important to consider the diagnosis of these rare small tumours pre-operatively, as it may be appropriate to manage this conservatively.

A case of multiple schwannomas of the trigeminal nerves, acoustic nerves, lower cranial nerves, brachial plexuses and spinal canal: schwannomatosis or neurofibromatosis?

In most cases, while schwannoma is sporadically manifested as a single benign neoplasm, the presence of multiple schwannomas in one patient is usually indicative of neurofibromatosis 2. However, several recent reports have suggested that schwannomatosis itself may also be a distinct clinical entity. This study examines an extremely rare case of probable schwannomatosis associated with intracranial, intraspinal and peripheral involvements. A 63-year-old woman presented with a seven-year history of palpable lumps on both sides of the supraclavicular area and hearing impairment in both ears. On physical examination, no skin manifestations were evident. Facial sensory change, deafness in the left ear and decreased gag reflex were revealed by neurological examination. Magnetic resonance imaging revealed multiple lesions of the trigeminal nerves, acoustic nerves, lower cranial nerves, spinal accessory nerve, brachial plexuses, and spinal nerves. Pathological examination of tumors from the bilateral brachial plexuses, the spinal nerve in the T8 spinal position and the neck mass revealed benign schwannomas. Following is this patient case report of multiple schwannomas presenting with no skin manifestations of neurofibromatosis.

Implementation of a clinical pathway in management of the postoperative vestibular schwannoma patient

OBJECTIVE

The purpose of the study was to evaluate the effectiveness of a new clinical pathway in management of patients with postoperative vestibular schwannoma. The impact on duration of hospitalization and quality of care was evaluated.

STUDY DESIGN

The study was a retrospective review of 59 consecutive patients undergoing surgical intervention for vestibular schwannoma between January 1995 and July 1999.

METHODS

A new clinical pathway for management of postoperative vestibular schwannoma patients was implemented at The California Ear Institute at Stanford (Palo Alto, CA) in January 1995. All patients undergoing surgical intervention subsequent to initiation of the pathway were included in the study. Data including surgical approach, patient age, sex, and tumor size were included. Duration of hospitalization and postoperative complications were recorded. During the same time period, data for patients undergoing radiation therapy for vestibular schwannomas were evaluated for length of hospital stay and in-hospital complications. Data were compared with norms recorded in the literature for duration of hospitalization and complications following surgical intervention.

RESULTS

Fifty-nine patients underwent 35 middle fossa approaches and 24 translabyrinthine approaches to their tumors. The average patient age was 53 years; there were 34 female and 25 male patients. The average length of hospital stay was 3.83 days (SD = 1.4 days) with a range from 2 to 10 days. Postoperative complications were observed in 19% of patients, including eight (13%) cerebrospinal fluid (CSF) leaks, two requiring lumbar drains (3.4%); one hematoma (1.6%), one postoperative fever (1.6%), and one dural tear with associated hyponatremia (1.6%). These results compared favorably with previously recorded average hospital stays of 5.95 to 9.5 days 1,5-7 and CSF leak complication rates of 7% to 15%.9,10

CONCLUSIONS

Implementation of a clinical pathway for management of the patient with postoperative vestibular schwannoma improves efficiency of patient care, allowing decreased duration of hospitalization. This goal is achieved without increasing complication rates and, in our experience, actually improving the quality of clinical care. The cost-effectiveness of clinical pathways may become increasingly important in a managed care-driven environment.

Hearing habilitation with auditory brainstem implantation in two children with cochlear nerve aplasia

Patients with aplasia and hypoplasia of the cochlear nerve have no chance of having their hearing restored by stimulating the periphery of the auditory system using the traditional cochlear implant. A possible approach to auditory rehabilitation may be direct electrical stimulation of the cochlear nuclei with an auditory brainstem implant (ABI). Recently, two children, aged 4 and 3 years, respectively, with bilateral severe cochlear malformations and cochlear nerve aplasia received an ABI. The present paper reports the technique and the preliminary results of this experience. The classic retrosigmoid approach was used. The correct position of the electrodes was estimated with the aid of EABRs and neural response telemetry (NRT). No postoperative complications were observed. High-resolution CT scans with a bone algorithm reconstruction technique were taken postoperatively to evaluate electrode placement before discharge. The ABI was activated 30 days after implantation in both patients. To date 16 and 13 electrodes, respectively, have been activated in the two children. Three months after activation the first patient had achieved good environmental sound awareness, good speech detection and some speech discrimination. The second child, 1 month after activation, had achieved good environmental sound awareness and moderate speech detection. To the best of our knowledge this is the first report of patients with hypoplasia of the cochlea and aplasia of the cochlear nerve, aged below 5 years and treated with an ABI.

Vestibular neurectomy

A brief history of the vestibular neurectomy is given. This treatment modality was introduced in Denmark by us, using the experiences obtained by the use of translabyrinthine treatment modality for vestibular schwannoma surgery. This paper presents our experiences with this type of surgery (translabyrinthine, retrolabyrinthine and retrosigmoid vestibular nerve section) from 1980 to 1996, including 43 operations in 42 patients. The patients had all been treated with conventional methods without success and were all severely handicapped by their attacks of vertigo. The mean age was 51 years, postoperative observation time between 2 and 15 years, with a mean of 6.4 years. The vertigo was controlled in 88% of the patients, while postoperative imbalance occurred in 14 patients, mainly due to the ablation of the vestibular labyrinth and not by episodic vertigo. A total of 39 patients indicated that they were satisfied with the operation. Six patients were deaf before surgery and 92% of the remaining patients retained their preoperative hearing. Postoperative complications were few, including two re-operations for CSF leaks, one patient with a slight transient facial nerve paresis and one transient VI nerve paresis. The results compare favorably with results from other authors. Retrosigmoid vestibular nerve section is an effective treatment modality to be offered to patients in whom other modalities have failed. Information about the efficacy and leniency of the treatment should be given to the patient's organization in order to diminish the fear of an intracranial intervention. Surgical experience is necessary in order obtain good results, the number of patients needing the operation is small and centralization of the treatment is mandatory.

Microvascular decompression for cochlear symptoms

OBJECT

The object of this study was to evaluate the efficacy of a new neurovascular decompression technique in relieving symptoms of cochlear nerve dysfunction.

METHODS

Nineteen patients with slowly progressive hearing loss, low-frequency fluctuating hearing loss, and high-pitched tinnitus due to neurovascular compression (NVC) of the eighth cranial nerve in a triangular space between the seventh and eighth cranial nerves (the VII-VIII triangle) of the cerebellopontine angle (CPA) were treated using a new technique for microvascular decompression that was developed by anatomical study in 24 cadaver specimens of the CPA. In 12 of 19 patients the anterior inferior cerebellar artery (AICA) was observed to cause compression in the VII-VIII triangle and this vessel was easily mobilized medially for placement of a silicone sponge or Teflon cushion between the compressing artery and nerve. Postoperatively, hearing loss of 20 dB or more that was present in 11 of the 19 patients with NVC improved by more than 5 dB in seven (64%), including the patient with the most severe hearing loss. Of 18 patients presenting with tinnitus preoperatively, eight (44%) had no tinnitus and an additional nine (for a total of 94%) had good improvement in tinnitus after surgery and at long-term follow up.

CONCLUSIONS

The microvascular decompression technique described is highly successful in treating symptoms due to direct or indirect compression of the cochlear nerve, with minimal risk of complications. Recordings of auditory brainstem responses confirmed the clinical diagnosis of NVC of the eighth cranial nerve and correlated with clinical results after microvascular decompression of the cochlear nerve.

Gamma surgery for vestibular schwannoma

OBJECT

The goal of this study was to assess the results of gamma surgery (GS) for vestibular schwannoma (VS) in 200 cases treated over the last 10 years and to review the role of this neurosurgical procedure in the management of VS.

METHODS

Follow-up reviews ranging from 1 to 10 years were available in 153 of these patients. Follow-up images in these cases were analyzed using computer software that we developed to obtain volume measurements for the tumors, and the clinical condition of the patients was assessed using questionnaires. Gamma surgery was the primary treatment modality in 96 cases and followed microsurgery in 57 cases. Tumors ranged in volume from 0.02 to 18.3 cm(3). In the group in which GS was the primary treatment, a decrease in volume was observed in 78 cases (81%), no change in 12 (12%), and an increase in volume in six cases (6%). The decrease was more than 75% in seven cases. In the group treated following microsurgery, a decrease in volume was observed in 37 cases (65%), no change in 14 (25%), and an increase in volume in six (11%). The decrease was more than 75% in eight cases. Five patients experienced trigeminal dysfunction; in three cases this was transient and in the other two it was persistent, although there has been improvement. Three patients had facial paresis (in one case this was transient, lasting 6 weeks; in one case there was 80% recovery at 18 months posttreatment; and in one case surgery was performed after the onset of facial paresis for presumed increase in tumor size). Over a 6-year period, hearing deteriorated in 60% of the patients. Three patients showed an improvement in hearing. No hearing deterioration was observed during the first 2 years of follow-up review.

CONCLUSIONS

Gamma surgery should be used to treat postoperative residual tumors as well as tumors in patients with medical conditions that preclude surgery. Microsurgery should be performed whenever a surgeon is confident of extirpating the tumor with a risk-benefit ratio superior to that presented in this study.

Management of intrameatal vestibular schwannoma

The growth of purely intrameatal vestibular schwannoma (VS) was investigated, in the period 1973-96 in a series of 40 patients with 40 unilateral VS. In the present study, the material was analysed and updated. By the end of the observation period (mean 3.6 years), 27 tumours (67.5%) revealed growth and 13 tumours (32%) had no measurable growth. Four growth patterns were observed: (A) 15 tumours (37.5%) exhibited constant growth; (B) 13 tumours (32.5%) had no measurable growth; (C) 8 tumours (20%) revealed growth subsequent to a no-growth period; and (D) 4 tumours (10%) showed different growth patterns during the observation period. The annual diameter growth rate ranged between 00 mm/year and 6.5 mm/year and the mean diameter growth per year was 3.2 mm. The findings of the present study, especially those for group B (the non-growing tumours) and C (tumour growth subsequent to a silent period) bring into question the reliability of the results achieved by radiosurgery, as without any intervention it may be that no tumour growth occurs.

[Vascular origin of cerebellopontine angle syndrome]

INTRODUCTION

The seventh and eighth cranial nerves course toward the internal auditory canal within the cerebellopontine angle. Lesions in this region are usually related to malfunctions of these cranial nerves. Although an acoustic schwannoma is one of the main etiologies of cerebellopontine angle pathology, various inflammatory processes and vascular anomalies even though rare must be considered.

PATIENTS/METHODS

We describe 5 cases with vascular loops of the basilar or vertebral arteries as a possible cause for hearing loss, vertigo and pulsatile tinnitus. In two cases the vascular lesion was confirmed at surgery, in which a decompression procedure was performed. The work-up for each patient included an auditory test battery and electronystagmography. Imaging studies included MRI and angiography in two cases.

RESULTS/CONCLUSIONS

Our experiences show that while the cerebellopontine angle syndrome is mostly caused by benign tumors an abnormal vascular loop has to be considered in any differential diagnosis.