The vibrant soundbridge for conductive and mixed hearing losses: European multicenter study results.

BACKGROUND/AIMS: The Vibrant Soundbridge (VSB) is an active middle ear implant, 'direct-drive' hearing system for the treatment of hearing loss. Recently, the VSB has been applied to conductive and mixed hearing losses. The aim of this study is to evaluate aided benefit, speech recognition in quiet and noise, subjective benefits, changes in residual hearing, and medical and surgical complications in adults with conductive or mixed hearing losses implanted with the VSB using Round Window (RW) Vibroplasty. METHODS: Twelve German-speaking adults participated in a single-subject, repeated measures study design comparing their performance using the VSB with their own unaided preoperative performance. Hearing performance and changes in residual hearing were assessed using routine audiometric measures, sound field thresholds, and word and sentence recognition in quiet and in noise. Subjective benefits, including subjective hearing performance, device satisfaction, and quality of life were evaluated using the Abbreviated Profile of Hearing Aid Benefit, the Hearing Device Satisfaction Scale, and the Glasgow Benefit Inventory, respectively. RESULTS: Aided hearing thresholds, word recognition at conversational levels, and sentence recognition in quiet and noise were significantly improved without significant changes in residual cochlear hearing and without major medical and surgical complications. One subject required repositioning surgery to improve transducer coupling with the RW membrane. Subjective benefit and device satisfaction were good, as were overall and general quality of life. CONCLUSION: The VSB, implanted using RW vibroplasty, is a safe and effective treatment for adults with conductive and mixed hearing losses who may have few, if any, other options.

Bionic ear imaging.

PURPOSE: The aim of this study was to illustrate the different imaging features of middle and inner ear implants, brainstem implants and inferior colliculus implants. MATERIALS AND METHODS: We retrospectively reviewed the computed tomography (CT) images of 468 patients with congenital or acquired transmissive or neurosensory hearing loss who underwent surgery. The implants examined were: 22 Vibrant Soundbridge implants, 5 at the long limb of the incus and 17 at the round window, 350 cochlear implants, 95 brainstem implants and 1 implant at the inferior colliculus. All patients underwent a postoperative CT scan (single or multislice scanner) and/or a Dentomaxillofacial cone-beam CT scan (CBCT) (axial and multiplanar reconstruction), and/or a plain-film radiography to visualise the correct position of the implant. RESULTS: The CBCT scan depicts Vibrant site of implant better than plain-film radiography, with a lower radiation dose compared to CT. For cochlear implants, a single plain radiograph in the Stenvers projection can directly visualise the electrodes in the cochlea. All patients with brainstem or inferior colliculus implants underwent postoperative CT to exclude complications and the assess correct implantation, but the follow-up of these implants can be performed by plain radiography alone. CONCLUSIONS: CT and CBCT scans are reliable and relatively fast methods for precisely determining the location of middle ear implants. CBCT is preferable to CT because of the lower radiation dose administered; a single plain-film radiograph is enough to visualise and follow-up cochlear, brainstem and inferior colliculus implants.

Auditory brainstem implant in posttraumatic cochlear nerve avulsion.

Patients aged over 12 years with neurofibromatosis type 2 are considered candidates for an auditory brainstem implant (ABI). This study extends the indication criteria of ABI to subjects with profound hearing loss due to damaged cochleas and/or cochlear nerves (CNs) following head injuries. In our department, over the period from April 1997 to November 2002, 32 patients, 23 adults and 9 children, were fitted with ABIs. Their ages ranged from 14 months to 70 years. These patients were suffering from a variety of tumor (13 subjects) and nontumor CN or cochlear diseases (19 subjects). Six patients, 5 adults and 1 child, had profound hearing loss following head injury. Their mean age was 25 years (range: 16-48 years). Five were male and 1 female. The retrosigmoid approach was used in all 6 patients. The electrode array was inserted into the lateral recess of the fourth ventricle and correct electrode positioning was monitored with the aid of electrically evoked auditory brainstem responses and neural response telemetry. Correct implantation was achieved in all patients. No complications were observed due to implantation surgery or related to ABI activation and stimulation of the cochlear nuclei. At activation, an average of 9.8 electrodes (range 5-13) were switched on without side effects. One to 6 electrodes were activated in the following sessions after time periods ranging from 2 to 16 months. All patients achieved auditory-alone-mode closed-set word recognition scores ranging from 40 to 100%; 3 had auditory-alone-mode open-set sentence recognition scores of 60-100%; 2 of these even had speech-tracking performance scores of 38 and 43 words, respectively, showing an ability to engage in normal conversation and converse over the phone. The present study demonstrates that the ABI is a useful rehabilitation instrument in subjects with damaged cochleas and/or CN avulsion following head injury who are unamenable or poorly responsive to auditory rehabilitation using cochlear implants.

[Cochlear implantation through the middle fossa approach]. / Implantacja wszczepu slimakowego z dojscia przez srodkowy dól czaszki.

The inner part of cochlear implant is inserted into inner ear during surgery through mastoid and middle ear. It is a classical method, used in the majority cochlear centers in the world. This is not a suitable method in case of chronic otitis media and middle ear malformation. In these cases Colletti proposed the middle fossa approach and cochlear implant insertion omitting middle ear structures. In patient with bilateral chronic otitis media underwent a few ears operations without obtaining dry postoperative cavity. Cochlear implantation through the middle fossa approach was performed in this patient. The bone fenster was cut, temporal lobe was bent and petrosus pyramid upper surface was exposed. When the superficial petrosal greater nerve, facial nerve and arcuate eminence were localised, the cochlear was open in the basal turn and electrode were inserted. The patient achieves good results in the postoperative speech rehabilitation. It confirmed Colletti tesis that deeper electrode insertion in the cochlear implantation through the middle fossa approach enable use of low and middle frequencies, which are very important in speech understanding.

The retrosigmoid approach for auditory brainstem implantation.

OBJECTIVE: To describe our experience with the retrosigmoid-transmeatal (RS-TM) approach in auditory brainstem implantation (ABI) as well as the anatomosurgical guidelines for this route. STUDY DESIGN: Retrospective case review. SETTING: Ear, Nose, and Throat Department of the University of Verona. PATIENTS: Five patients with neurofibromatosis type 2 (NF2) were operated on for vestibular schwannoma removal with ABI implantation from April 1997 to June 1999. The patients were four men and one woman, whose ages ranged from 22 to 37 years. The tumor sizes ranged from 12 to 30 mm. The records of a total of 179 patients operated on for vestibular schwannoma (VS) removal via the RS-TM approach from January 1990 to June 1999 were also evaluated. Their ages ranged from 18 to 88 years (average 54 years). The tumor sizes ranged from 4 to 50 mm. Five patients had a solitary VS in the only hearing ear. INTERVENTION: The classic RS-TM approach was used in all patients. After tumor excision, for ABI implantation, the landmarks (seventh, eighth, and ninth cranial nerves, choroid plexus) for the foramen of Luschka were carefully identified. The choroid plexus was then partially removed, and the tela choroidea was divided and bent back. The floor of the lateral recess of the fourth ventricle and the convolution of the dorsal cochlear nucleus became visible. The electrode array was then inserted into the lateral recess and correctly positioned with the aid of electrically evoked auditory brainstem responses (EABRs). MAIN OUTCOME MEASURES: Intraoperative EABR and postoperative speech perception evaluation. RESULTS: Auditory sensations were induced in all patients with various numbers of electrodes. Different pitch sensations could be identified with different electrode stimulation. CONCLUSIONS: In the authors' experience, the RS-TM approach is the route of choice for patients who are candidates for ABI when there is a chance of hearing preservation during surgery. If auditory function is lost during surgery, anatomical preservation of the cochlear nerve may allow hearing restoration with a cochlear implant. Direct intraoperative recording of cochlear nerve action potentials (CNAPs) and round window electrical stimulation are mandatory for these purposes. In addition, decompression of the intrameatal portion of the vestibular schwannoma and planned partial tumor resection with hearing preservation are also possible with the RS-TM approach.

New approach for cochlear implantation: cochleostomy through the middle fossa.

The middle fossa approach was used in 11 patients with profound bilateral hearing loss for insertion of a cochlear implant. Fibroadhesive otitis media (n = 1), bilateral cavity radical mastoidectomy (n = 1), autoimmune inner ear disease (n = 2), previous cranial trauma (n = 1), genetic prelingual deafness (n = 5), and otosclerosis (n = 1) were the causes of deafness. A cochleostomy was performed on the most superficial part of the basal turn, and the electrode array was inserted up to the cochlear apex. Speech perception tests (1-9 months after cochlear implant activation) yielded better results in these patients compared with a homogeneous group of postlingually deaf patients operated on through the traditional transmastoid route. Insertion of the implant through the middle fossa cochleostomy furnishes the possibility of stimulating areas of the cochlea (ie, the middle and apical turns) where a greater survival rate of spiral ganglion cells is known to occur, with improvement of information regarding the formants relevant for speech perception.

Medical treatment in Ménière's disease: avoiding vestibular neurectomy and facilitating postoperative compensation.

The efficacy of medical treatment in preventing the need for vestibular neurectomy (VN) in patients with disabling Ménière's disease, and in facilitating postoperative compensation of equilibrium after VN, was investigated. Ninety-five patients with classic symptoms of unilateral incapacitating Ménière's disease were included. Patients were treated with either 16 mg betahistine three-times daily (n = 49) or 125 mg acetazolamide once-daily (n = 46) for 6 months. The study showed that marked benefit was achieved in 51 of the 95 patients, of whom significantly more were in the betahistine group than in the acetazolamide group [32 (65%) vs 19 (41%); p < 0.05]. Twenty-seven patients in the acetazolamide group and 17 in the betahistine group experienced no benefit from medical treatment and therefore underwent VN. Twelve patients in the betahistine group and 6 in the acetazolamide group eventually experienced a relapse and thus also underwent VN. Therefore 62 patients in total underwent VN. Following surgery, patients were given medical treatment in an attempt to facilitate vestibular compensation; 28 received betahistine (16 mg three-times daily) and 34 received cinnarizine (25 mg three-times daily) for 3 months. The patients treated with betahistine had a shorter period of disability and significantly better results on rotatory testing. In conclusion we recommend the use of betahistine in patients who have undergone VN.

Retrosigmoid approach for auditory brainstem implant.

The present paper reports our experience with the surgical retrosigmoid-transmastoid (RS-TM) technique for implanting auditory brainstem implants (ABIs). From April 1997 to August 1998, four patients with neurofibromatosis type 2 (NF2) were operated on for vestibular schwannoma removal with ABI implantation. The subjects (three men and one women) ranged in age from 22 to 31 years. Tumour size ranged from 12 to 30 mm. A classical RS-TM approach was performed. After tumour excision, identification of landmarks (VIIth, VIIIth and IXth cranial nerves, choroid plexus) to the foramen of Luschka was carefully carried out. The choroid plexus was partially removed and the tela choroidea divided and deflected. The floor of the lateral recess of the fourth ventricle and the convolution of the dorsal cochlear nucleus became visible. The electrode array was then inserted into the lateral recess and placed in the correct position with the help of electrically-evoked auditory brain stem responses. Auditory sensations were induced in all patients with various numbers of electrodes. Different pitch sensations could be identified with different electrode stimulation. Details of the results are presented. In our series, the RS-TM approach represents the elective route for ABI insertion.

Advantages of the retrosigmoid approach in auditory brain stem implantation.

From April 1997 to December 1999, six patients (five men and one woman), ranging in age from 22 to 37 years with neurofibromatosis type 2 (NF2) were operated on via the classic retrosigmoid-transmental (RS-TM) approach for removal of a vestibular schwannoma (VS) (tumor size from 12 to 40 mm) and for auditory brain stem implantation (ABI). After tumor removal, the floor of the lateral recess of the fourth ventricle and the convolution of the dorsal cochlear nucleos were reached, and the ABI was inserted. More recently, an ABI was implanted via the retrosigmoid approach in a 4-year-old boy with a cochlear malformation (common cavity) associated with cochlear nerve aplasia. Electrically evoked auditory brain stem responses (EABRs) and neural response telemetry (NRT) were performed to verify the correct positioning of the inserted electrodes. No major complications related to ABI were observed. ABI has been activated to date in five of the NF2 patients. Auditory sensations with various numbers of electrodes were evoked in all patients. We consider the RS-TM approach the route of choice for ABI insertion in patients with NF2 and good hearing, offering a chance of hearing preservation, and in patients with complete cochlear ossification, severe head trauma and cochlear fracture, or nerve disruption, or a combination of these. A new indication for ABI implantation via the RS approach is presented by patients with bilateral cochlear nerve aplasia.

Intraoperative monitoring for hearing preservation and restoration in acoustic neuroma surgery.

The present article reports on our experience with hearing preservation during 158 acoustic neuroma (AN) operations via the retrosigmoid-transmeatal (RS-TM) approach with the aid of intraoperative auditory monitoring. Several auditory monitoring methods are described. Of these, the bipolar cochlear nerve action potential (CNAP) was found to be the most helpful in preserving hearing. Of 106 patients with useful hearing preoperatively, more than 50% had useful hearing after surgery. Electrical auditory brainstem responses were useful in the placement of an auditory brain stem implant (ABI) in 4 patients with neurofibromatosis type 2 (NF2). All 4 reported speech perception benefit and use their ABIs regularly in their lives. It is our firm belief that intraoperative auditory monitoring has a pivotal role in the preservation and restoration of hearing in AN surgery.

Malleus-to-footplate prosthetic interposition: experience with 265 patients.

Absence of the long process of the incus with or without absence of the stapes head accounts for more than 80% of ossicular discontinuities. Total or partial replacement prostheses, made of various materials, are interposed to restore the transfer function of the middle ear. To simplify ossicular reconstruction, reduce operative times and costs, improve functional outcomes, and avoid the risk of infections, we have adopted, during the past 10 years, a technique that makes use of a personally designed alloplastic prosthetic device. The prosthesis connects the malleus to the footplate, even in the presence of the stapes superstructure. This malleus-to-footplate prosthesis consists in a plastipore-coated steel piston and hydroxyapatite head, complete with a groove. The groove is placed beneath the malleus neck after dissection of the tensor tympani tendon and the shaft of the piston on the footplate. Two hundred ninety primary ossiculoplasties with the malleus-to-footplate prostheses were performed in 265 patients from 1986 to 1995 in the ENT Department of the University of Verona. The average postoperative air-bone gap at 0.5 to 3 kHz was 11 dB at 1 year and 14 dB at 5 years. These outcomes are significantly better than those personally obtained previously with ossicular or alloplastic prostheses. No extrusions occurred. The structural characteristics of the malleus-to-foot-plate prosthesis endow the prosthesis with a high degree of biocompatibility and stability and optimal sound-transfer function. The rationale for this particular ossiculoplasty procedure is discussed.

Retrosigmoid-transmeatal en bloc removal of small to medium-sized acoustic neuromas.

One hundred three subjects with acoustic neuroma (AN) underwent surgery--involving a retrosigmoid-transmeatal approach--between January 1990 and December 1995. All the intracanalar tumors (n = 18) and 70 of the intra- and extracanalar neuromas with an extracanalar neuroma size less than 25 mm--a total of 88 patients--constituted the final study population. The first 48 patients were operated on with the use of classic procedures described in the literature, characterized by limited exposure of the internal auditory canal and removal of the tumor after debulking. Surgery in the next 40 subjects was conducted according to the technique of en bloc removal of the tumor. The main features of this technique are continuous direct recording of cochlear and facial-nerve action potentials, wide opening of the internal auditory canal with lateral extension to the fundus, and removal of the tumor following the capsular lining without debulking. Statistical analysis of the results of the en bloc removal, compared with the previously used debulking technique, showed improvement in postoperative outcome for both auditory and facial-nerve function.

Advances in monitoring of seventh and eighth cranial nerve function during posterior fossa surgery.

OBJECTIVE: This study aimed to illustrate some recent advances in intraoperative monitoring of the seventh and eighth cranial nerves (i.e., direct recording of cochlear nerve action potentials [CNAPs] and facial nerve action potentials [FNAPs]). STUDY DESIGN: Reports of representative cases and average postoperative results obtained in subjects submitted to cerebellopontine angle surgical procedures are examined. Results obtained in patients with direct recording techniques are compared with those obtained with the classical monitoring techniques (auditory brain stem response [ABR], electrocochleography [ECoG], facial electromyography [EMG]). SETTING: The study was conducted at an Ear Nose and Throat Department, University of Verona, Verona, Italy. INTERVENTION: Intraoperative monitoring during cerebellopontine angle surgery was performed. RESULTS: Patients monitored with direct audiomonitoring techniques presented better postoperative auditory functions compared to patients monitored with ABR. The FNAP and EMG groups showed FN outcome that did not differ significantly. CONCLUSIONS: Intraoperative monitoring of cranial nerves furnishes a valid tool for identification of neural structures, prevention of damage, understanding of the pathophysiology of damage, and prediction of postoperative function. The fundamental prerequisite for obtaining optimal benefits from monitoring is the use of techniques of direct and continuous electrophysiologic recording with instantaneous feedback to the surgeon, such as CNAPs and FNAPs.

ECochG, CNAP and ABR monitoring during vestibular Schwannoma surgery.

Identification of the specific pathophysiological processes and correlation with post-operative hearing are the prerequisites for utilizing electrophysiological audio monitoring techniques in preventing damage to auditory structures during vestibular Schwannoma (VS) surgery. The present paper compares the value of auditory brainstem responses (ABRs), electrocochleography (ECochG) and directly recorded cochlear nerve action potentials (CNAPs) in detecting damage to auditory structures during VS surgery and predicting post-operative hearing. Eighteen consecutive patients operated on for VS, in an attempt at hearing preservation, participated in the investigation. The ipsilateral hearing level (pure tone average [PTA] 0.5-3 kHz) ranged from 10 to 50 dB HL (mean: 30.7 dB HL), with a speech discrimination score equal to or better than 50 per cent. CNAPs furnished the highest predictive score for post-operative hearing. In particular, when a permanent loss of CNAPs occurred the sensitivity and specificity were 100 per cent. The discrepancies between the ECochG and CNAP findings were attributable to high prevalence of cochlear nerve damage, capable of 'disconnecting' the ear from the central auditory pathways, causing persistence of peripheral auditory function and no propagation of the neural input. ABR monitoring was highly sensitive in detecting auditory damage but its prognostic utility was marred by its poor specificity.

Intraoperative monitoring of facial nerve antidromic potentials during acoustic neuroma surgery.

The present paper presents monopolar recording of facial nerve antidromic potentials as an alternative technique to facial electromyography for the continuous monitoring of the facial nerve during acoustic neuroma surgery. The investigation involved 22 patients undergoing acoustic neuroma surgery via a retrosigmoid approach (tumour sizes ranging from 5 to 28 mm). Bipolar electrical stimulation of the marginalis mandibulae was performed to elicit facial nerve antidromic potentials. Stimulus intensity ranged from 2 to 6 mA with a delivery rate of 7/sec. A silver wire monopolar electrode positioned intracranially on the proximal portion of the acoustic facial bundle was used to record antidromic potentials. To define the specific origin of the action potentials and acquire normative data, monopolar and bipolar recordings of facial nerve antidromic potentials were performed in 15 subjects undergoing retrosigmoid vestibular neurectomy for Meniere's disease. The average facial nerve antidromic potential latency was 4.2 (+/- 0.6) msec in subjects with acoustic neuroma and 3.3 (+/- 0.2) msec in subjects with Meniere's disease. Facial nerve antidromic potentials furnished near real-time information about intraoperative facial nerve damage and postoperative facial nerve function during acoustic neuroma surgery. Facial nerve antidromic potentials may provide additional information to conventional EMG. They allow the use of endplate blockers, yield quantitative estimation of facial nerve conduction properties in terms of amplitude and latency, and allow actual continuous monitoring of the facial nerve.

"En-bloc" removal of small- to medium-sized acoustic neuromas with retrosigmoid-transmeatal approach.

Surgery of acoustic neuroma (AN) has significantly refined over the past years due to a series of advances in diagnostics and surgical technique. Electrophysiologic investigation performed during surgery has greatly contributed to this progress, increasing the surgeon's understanding of the mechanism of damage and suggesting various changes in his or her surgical strategy.In this context, the advantages of the retrosigmoid "en-bloc" removal of small to medium size ANs have been examined in the present study. At the ENT Department of the University of Verona, 103 subjects with AN were operated on, from January 1990 to December 1995, with a retrosigmoid-transmeatal approach. Eighteen subjects (17.4%) presented pure a intracanalar (IC) tumor and 85 (82.6%) had both IC and extracanalar (EC) involvement. All the IC tumors (n = 18) and 70 of the IC-EC neuromas with an EC size less than 25 mm are reported in this paper for a total of 88 patients. The first 48 patients were operated on via the classic procedures described in the literature, characterized by removal of the tumor after "debulking" and limited exposure of the internal auditory canal (IAC). The following 40 subjects were operated on according to the technique of "en-bloc" removal of the tumor and wide exposure of the IAC.In the "en-bloc" group the tumor was first detached from the cerebellar flocculus and the pons, when necessary. The tumor was not debulked to preserve the anatomic relationship with the nerves and to facilitate identification, cleavage and dissection of the tumor from the neural structures. Thereafter, the posterior wall of the IAC was drilled out and opened in a circumferential range from 180 to 270 degrees . The IAC dura was subsequently opened, and the distal end of the AN along with the vestibular nerves were identified. The vestibular nerves were sectioned in the distal portion of the IAC and dissected with the tumor from the underlying facial and cochlear nerves. Dissection continued medially to the IAC porus. The AN was progressively dissected from the cochlear and facial nerves in the cerebellopontine angle (CPA) with multiple direction maneuvers, as required by the characteristics and degree of adherence to the neural structures.The anatomic and functional results obtained with this new procedure ("en-bloc" removal) were compared with the classic "debulking" technique. The statistical analysis shows an improvement in postoperative outcome for both auditory and facial nerve function. The "en-bloc" removal procedure along with the wide exposure of the content of the IAC and electrophysiologic monitoring of the seventh and eighth cranial nerves are, in our experience, the recommended strategies for improving outcomes in small to medium size ANs.

Mechanisms of auditory impairment during acoustic neuroma surgery.

Hearing loss during removal of acoustic neuroma (AN) may be due to labyrinthine and/or neural and/or vascular damage. Surgical maneuvers relating to perioperative and postoperative hearing may give rise to mechanisms of auditory impairment. Recording action potentials from the intracranial portion of the cochlear nerve (CN) has proven particularly useful for identifying the mechanisms of iatrogenic auditory injury. In this paper intraoperative and postoperative auditory impairments are investigated in relation to surgical steps in a group of 47 subjects with AN (size ranging from 5 to 25 mm) undergoing removal by a retrosigmoid-transmeatal approach. Drilling of the internal auditory canal (IAC), removal of the AN from the IAC fundus, coagulation close to the CN, lateral to medial tumor traction, separation of the CN from the facial nerve, and stretching of the CN have proven to be the most critical surgical steps in hearing preservation. On the other hand, maneuvers such as intracapsular tumor removal, vestibular neurectomy, suction close to the AN, and closure of the IAC defect did not correlate with changes in auditory potentials. Predisposing factors to postoperative hearing deterioration were IAC enlargement greater than 3 mm, IAC tumor size greater than 7 mm, extracanalar tumor size greater than 20 mm, labyrinth medial to the IAC fundus, severe involvement of the CN in the IAC, preoperative abnormal auditory brainstem responses, and normal vestibular reflectivity. Age and preoperative hearing did not prove to be statistically related to postoperative hearing. The variations in morphology and latency of CNAPs are discussed in relation to the mechanisms of iatrogenic injury.

Utility and safety of parotid gland biopsy in Sjögren's syndrome.

Parotid gland biopsy was performed in 32 female patients affected by suspected Sjögren's syndrome. In all cases histologic findings were in agreement with this diagnosis and in two subjects led us to detect the malignant transformation into lymphoma. None of the patients developed relevant complications. Our study indicates that parotid gland biopsy in Sjögren's syndrome is a safe procedure and may be useful in performing diagnosis.

New perspectives in intraoperative facial nerve monitoring with antidromic potentials.

Electromyographic (EMG) activity recorded from the facial muscles in response to electrical and mechanical stimulation is the most popular method for continuous monitoring of the facial nerve during cerebellopontine-angle surgery. EMG recording is, however, extremely sensitive to the administration of neuromuscular blockers. An alternative technique for the continuous monitoring of the facial nerve [i.e., monopolar recording of facial nerve antidromic potentials (FNAPs)], is described. Ten subjects undergoing retrosigmoid vestibular neurectomy for Meniere's disease and 11 subjects operated on with acoustic neuroma surgery via a retrosigmoid approach (tumor size range, 12-28 mm) participated in the investigation. Bipolar electrical stimulation of the marginalis mandibulae was performed to elicit FNAPs. Stimulus intensity ranged from 0 to 10 mA with a delivery rate of 7/s. Antidromic potentials were recorded with a silver-wire monopolar electrode positioned intracranially on the proximal portion (root entry zone) of the acoustic-facial bundle. Bipolar recordings with two silver electrodes were also performed from the trigeminal and facial nerves in the cerebellopontine angle to define the specific origin of the action potentials. FNAP amplitude increased as a function of stimulus intensity. The average latency was 3.35 ms (range, 3.0-3.7 ms). Action potentials recorded intracranially during electrical stimulation of the marginal nerve originated specifically from the facial nerve. Changes in latency and amplitude of FNAPs were analyzed as a function of the main surgical steps in patients operated on for acoustic neuroma. FNAP monitoring provided quantitative real-time information about damaging maneuvers performed on the nerve and postoperative facial function.

Extrusion of corpora amylacea from the marginal gila at the vestibular root entry zone.

We have studied the vestibular nerve in patents suffering from Meniere' s disease and vascular cross-compression syndrome of the root entry zone due to close contact with the nerve of the antero-inferior cerebellar artery or one of its branches. All patients underwent vestibular neurectomy using the restrosigmoid approach which allows the resection of a relatively long nerve segment. In all the studied vestibular nerves a central and a peripheral zone could be distinguished. In the central zone, a massive accumulation of corpora amylacea (CA) was detected in the cytoplasm of astrocytes. Many CA were seen to protrude from the central nervous system into the pial connective tissue. These structures resembled sessile or predunculated polyps, with a complex system of scissurae at their bases. CA were also found in extracellular location in the pial connective tissue near capillaries, and not wrapped by membranes. Our findings suggest that after their production in astrocytes, CA are transferred into a pial connective tissue across the glial-limiting lamina. Thus, the present results indicate that CA do not merely represent an accumulation of abnormal material, but they could instead be part of a glio-pial system devoted to the clearance of substances from the nervous system.