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PubMed1992

Electrical evaluation of the facial nerve in acoustic neuroma patients: preliminary comparison between transcranial magnetic coil stimulation and electroneurography.

Subclinical involvement of the facial nerve by acoustic neuromas may be identified preoperatively using conventional electroneurography (ENoG). The clinical application of extratemporal stimulation distal to the stylomastoid foramen is limited in these cases by the more proximal site of the lesion. Transcranial magnetic coil stimulation (MCS) is a noninvasive means by which the facial nerve is stimulated at the level of the motor cortex or the brain stem, before it enters the internal auditory canal. Topographically such an assessment may have more diagnostic relevance than other forms of electrical stimulation in acoustic neuroma patients. To test this theory the facial nerves of 20 patients with acoustic neuromas were stimulated using ENoG and MCS preoperatively and 1 week postoperatively. Stimulation parameters were comparable and included threshold and suprathreshold levels of stimulation while compound action potential amplitudes and early and late response latencies were monitored. Facial nerve function was assessed clinically using the Stennert grading system. All the patients had clinically normal facial nerve function preoperatively. Normative data suggested a close correlation between threshold and suprathreshold amplitudes generated by both ENoG and MCS. To the contrary, in the pathologic ears there was a higher incidence of stimulus response abnormality determined by MCS than by ENoG. A comparison of these data, tumor size, and postoperative results promotes further evaluation of MCS as a prognostic index in acoustic neuroma patients.

Action Potentials↗
PubMed1991

[Neurilemmomatosis--a sporadic and familial cases].

Three cases of neurilemmomatosis are reported. A 22-year-old man without any relatives with similar symptoms visited our clinic, complaining of multiple skin tumors since the age of 15 and bilateral acoustic nerve symptoms since 19. Physical examination revealed no pigmented or depigmented spots. Histopathological examination of the eight tumors excised from the skin, acoustic nerve and spinal cord showed that these were all neurilemmomas. A 36-year-old man with a 15 year history of multiple skin tumors and one year history of acoustic nerve symptoms was seen at our clinic, revealing no pigmentary disorders. The tumors excised from the skin and bilateral acoustic nerves were all neurilemmomas histopathologically. A 5-year-old boy, who was the only child of the second case and had had several skin tumors since his birth, visited us after postoperative death of his father. He revealed no pigmentary abnormalities. The histology of the skin tumor was neurilemmoma. The absence of neurofibromas and pigmented spots in these patients with neurilemmomatosis suggests that this disorder might be close to, but distinct from neurofibromatosis. Although familial cases of neurilemmomatosis like our case 2 and 3 reported so far are very few, they support a possibility that neurilemmomatosis might be a genetically determined neurocutaneous syndrome, a kind of phacomatosis.

Adult↗
PubMed1992

Intraoperative monitoring of facial and cochlear nerves during acoustic neuroma surgery.

The likelihood of successful preservation of facial and cochlear nerve function during acoustic neuroma surgery has been improved by the advent of intraoperative monitoring techniques. The facial nerve is monitored by recording EMG from facial muscles, with no muscle relaxants used; mechanical irritation of the nerve during surgery causes increased EMG activity, which can be detected in real time using a loudspeaker. Brief episodes of activity associated with specific surgical maneuvers aid the surgeon in avoiding damage to the nerve, whereas prolonged tonic EMG activity may reflect significant neural injury. Electrical stimulation with a hand-held probe elicits evoked EMG responses, which can be used to locate and map the nerve in relation to the tumor. The threshold for eliciting evoked EMG responses provides a rough indicator of the functional status of the nerve. Different nerves in the posterior fossa (trigeminal, facial, spinal accessory) can be identified in multichannel recordings by the spatial distribution and latency of responses to electrical stimulation. The ability to elicit EMG responses from low amplitude stimulation of the facial nerve at the brain stem after tumor removal is a reasonable predictor of postoperative facial function. Cochlear nerve function is assessed by recording the ABR from ear canal and scalp electrodes or the CNAP with an electrode placed directly on the nerve at the brain stem root entry zone. The ABR is a well-known, noninvasive technique that can be adapted to intraoperative use relatively easily but is of limited utility owing to the delay inherent in signal averaging. Direct CNAP recordings require placement of an intracranial electrode in such a way as to contact the cochlear nerve without interfering with surgical access but have the distinct advantage of rapid feedback on changes in cochlear nerve status.

Cochlear Nerve↗
PubMed2000

Combined transhorizontal-supracerebellar approach for microvascular decompression of trigeminal neuralgia.

A combined approach for microvascular decompression of trigeminal neuralgia is reported. Arachnoid dissection of the cerebellar horizontal fissure (transhorizontal approach) allowed easy identification of the root exit zone of the trigeminal nerve. The superior semilunar lobule was pulled back rostrally so that retraction of the acoustic nerve was minimal. After identification of the offending vessels, the supracerebellar artery was mobilized and dissected out through the supracerebellar route, which was also less invasive to the acoustic nerve than the standard approach. By combining these two approaches, the whole surface of the trigeminal nerve can be observed easily. Thus, the offending vessels can be readily identified, mobilized and moved away from the trigeminal nerve with minimal retraction of the acoustic nerve.

Adult↗
PubMed2006

Descriptive epidemiology of vestibular schwannomas.

Vestibular schwannomas, commonly termed acoustic neuromas, arise from the vestibular branch of the eighth cranial nerve (acoustic nerve) and are benign, slow-growing brain tumors that negatively impact patient quality of life. They are thought to account for the majority of intracranial nerve sheath tumors. To describe incidence rate patterns and trends of primary nerve sheath tumors of the brain/CNS and the subset of vestibular schwannomas in two population-based incidence registries, data were obtained from 11 Central Brain Tumor Registry of the United States (CBTRUS) collaborating state registries and the Los Angeles County Cancer Surveillance Program (LACCSP) (1975-1998). Average annual incidence rates were tabulated by age, gender, race, year, and region and were age-adjusted to the year 2000 U.S. standard population. Multiplicative Poisson regression models were used to compare trends in primary nerve sheath tumors of the brain/CNS overall and in subgroups, including vestibular schwannomas, controlling for age, gender, race, microscopic confirmation, and region. Joinpoint regression analysis was used to identify any sharp changes in incidence over time. The overall incidence of primary nerve sheath tumors of the brain/CNS was 1.1 per 100,000 person-years (CBTRUS, 1995-1999 and LACCSP, 1995-1998). The incidence of vestibular schwannomas was similar for both data sets: 0.6 per 100,000 person-years (CBTRUS, 1995-1999) and 0.8 per 100,000 person-years (LACCSP, 1995-1998). Moreover, the incidence of primary nerve sheath tumors of the brain/CNS overall (CBTRUS, 1985-1999 and LACCSP, 1975-1998) and of vestibular schwannomas (CBTRUS, 1992-1999 and LACCSP, 1992-1998) increased over time. However, the incidence of benign schwannomas in sites other than the acoustic nerve either decreased (CBTRUS, 1992-1999) or experienced no significant change (LACCSP, 1992-1998). While improvements in diagnosis and reporting may explain some of these trends, further consideration of potential etiologic factors may be warranted.

Adolescent↗
PubMed1983

Wave I of early auditory evoked potentials in multiple sclerosis.

Early auditory evoked potentials (EAEPs) were recorded in a series of 71 consecutively examined patients suffering from clinically definite or probable multiple sclerosis (MS). Wave I abnormalities, i.e., delayed latency, with or without reduced amplitude, were observed in 15 such patients and were interpreted as due to MS in 8 of them. As EAEP wave I is identical with the potential N1 in electrocochleography and corresponds to activity of the most distal part of the acoustic nerve or the spiral ganglion, it is concluded that the peripheral part of the acoustic nerve is involved in about 10% of MS patients. In two cases normalization of initially delayed wave I latencies were demonstrated during follow-up recording. The pattern of a late wave I but normal hearing in 3 patients is interpreted in terms of a desynchronized compound nerve activity with fully preserved conductivity, segmental demyelination of a considerable number of acoustic nerve fibres being the most likely cause.

Auditory Perception↗
PubMed1998

Cochlear implantation in osteogenesis imperfecta.

A case is reported in which a Nucleus 22 channel intracochlear implant was applied to a Hungarian woman (age 50 yr) with profound deafness associated with osteogenesis imperfecta. Successful intracochlear insertion of the 22 electrodes resulted in a 70 dB hearing improvement at frequencies 250-2000 HZ. Nevertheless, a characteristic facial twitching appeared upon activation of electrodes 9-13. Inactivation of these electrodes abolished the non-acoustic nerve excitation with preservation of acoustic performance. Osteogenesis imperfecta may involve a state of risk for non-acoustic nerve activation in cochlear implant patients possibly resulting from a reduced impedance to current spread by abnormal bone tissue. This, however can be overcome by simple programming manoeuvres.

Cochlear Implantation↗
PubMed2003

An auditory-periphery model of the effects of acoustic trauma on auditory nerve responses.

Acoustic trauma degrades the auditory nerve's tonotopic representation of acoustic stimuli. Recent physiological studies have quantified the degradation in responses to the vowel /E/ and have investigated amplification schemes designed to restore a more correct tonotopic representation than is achieved with conventional hearing aids. However, it is difficult from the data to quantify how much different aspects of the cochlear pathology contribute to the impaired responses. Furthermore, extensive experimental testing of potential hearing aids is infeasible. Here, both of these concerns are addressed by developing models of the normal and impaired auditory peripheries that are tested against a wide range of physiological data. The effects of both outer and inner hair cell status on model predictions of the vowel data were investigated. The modeling results indicate that impairment of both outer and inner hair cells contribute to degradation in the tonotopic representation of the formant frequencies in the auditory nerve. Additionally, the model is able to predict the effects of frequency-shaping amplification on auditory nerve responses, indicating the model's potential suitability for more rapid development and testing of hearing aid schemes.

Animals↗
PubMedDate not supplied

Electrically evoked auditory brainstem response by direct electrical stimulation to the cochlear nerve in acoustic neuroma patients.

The electrically evoked auditory brainstem response (EABR) was recorded by direct electrical stimulation of the cochlear nerve in 8 acoustic neuroma patients. The EABR by electrical stimulation of the cochlear nerve at the fundus of the internal auditory canal was almost similar to those previously reported from cochlear implant patients in waveform morphology and wave latencies. However, the wave corresponding to wave II in human auditory ABR was not recorded in the EABRs by stimulation of the distal part of the intracranial cochlear nerve. These results suggest that the cochlear nucleus does not contribute to the generation of wave II in ABR.

Adult↗
PubMed1976

[A case of reversible deafness in cystic arachnoiditis (author's transl)].

A patient studied preoperatively by a neuro-otological test battery showed signs of an extensive cerebellopontine angle tumour. During the operation dense fibrotic tissue was found extending from the choroid plexus to the right acoustic nerve, which was freed and thus decompressed. Postoperatively, low frequency hearing improved markedly in the right ear. In contrast to the well-known documented cases of successful decompression of the optic nerve it has not been possible up to now to achieve a successful outcome in similar procedures on the acoustic nerve. In the described case the fibrotic lesion had obviously just caused reversible damage to the myelin sheaths of the eighth nerve, which can be interpreted as "neurapraxia" (Seddon, 1943). Further investigations in regard to the systematic elucidation of possibly reversible damage to the acoustic nerve are currently being performed at the IInd ENT department of Vienna University.

Aged↗
PubMed1990

[Postoperative MR findings in acoustic neuromas: nerve edema within the internal auditory canal].

Postoperative MR findings of eleven acoustic neuromas were analyzed. MRI's were able to clearly visualize residual tumor around the 7th and 8th cranial nerves that were left to preserve cranial nerve function, although conventional X ray CT scans often failed to detect it due to artifacts in the parapetrous area. The facial nerves preserved during operations were also visualized from their brainstem portion to the internal auditory meatus. These findings indicate that MRI is excellent in delineating soft tissue in the CP angle that would be overlooked by conventional X ray CT scan. It was also found that the nerve bundles within the internal auditory canal gained increased signal intensity on the T1 and proton weighted images after surgical interventions and that this effect extended into the most distal end of the nerve bundles and even into the intracochlear portion of the cochlear nerve. The nerve bundles with increased signal intensity were conspicuously enhanced after intravenous administration of Gd-DTPA. This indicated that the blood nerve barrier of the nerves within the internal auditory canal were disrupted due to the surgical manipulations in excising tumors. Following such surgical manipulations, nerve edema ensued, although manipulations in the cerebello-pontine angle were done carefully and protectively under a surgical microscope. The clinical significance of disruption of the blood nerve barrier and following nerve edema were discussed from the standpoint of preservation of the 7th and 8th cranial nerve functions.

Blood-Brain Barrier↗
PubMed1994

Calcium and calmodulin inhibit phosphorylation of a novel auditory nerve protein.

The growing use of cochlear prosthetic devices and demonstrations of direct ototoxic insult to spiral ganglion neurons make it imperative to gain an understanding of intracellular biochemical regulation in primary sensory neurons. Calcium and calmodulin regulate many aspects of neuronal cellular physiology through stimulation of protein kinase activity. We have previously demonstrated the presence of calmodulin-dependent protein kinase substrates in the guinea pig modiolus and, additionally, the presence of two proteins (12 kDa and 81 kDa, designated as p12 and p81) whose phosphorylation is blocked by calcium and calmodulin (Coling and Schacht, 1991). Here, we investigate three models for this unusual regulatory mechanism. The effects of calcium, calmodulin and trifluoperazine on dephosphorylation of both proteins suggests that calmodulin inhibits protein kinase activity. P81 was identified by immunoprecipitation as the myristoylated alanine-rich C kinase substrate (MARCKS), a ubiquitous actin-binding protein. Two observations indicate that MARCKS may be regulated differently in acoustic nerve than in cerebral cortex. 32P incorporation was significantly higher in acoustic nerve than in brain. The calmodulin-dependent block of MARCKS phosphorylation was observed only in acoustic nerve. p12 shares several characteristics with myelin basic protein (MBP). We used a double label assay with 32P autoradiography and immunoblotting to show that p12 is in fact distinct from MBP. We suggest that either p12 or p12 kinase may be either specific to the peripheral auditory system or novel marker proteins for that tissue.

Animals↗
PubMed1991

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.

Electromyography↗
PubMed1993

[A case of superficial siderosis of the central nervous system with total deafness].

Superficial siderosis of the central nervous system (SSCN) in a disease characterized by chronic deposition of hemosiderin in the leptomeninges, subpial tissue, spinal cord, and cranial nerves. Previously the diagnosis of SSCN could only be made at autopsy or during a neurosurgical procedure. Now, however, a diagnosis of SSCN can be made non-invasively by magnetic resonance imaging (MRI). We present the case of a 50-year-old male with SSCN accompanied by bilateral sensorineural hearing loss which gradually progressed to total deafness over a seven year period. This patient also had associated bilateral caloric weakness with episodes of severe recurrent headaches over the two preceding years. The deafness and gait disturbance, which were his chief complaints, were followed by other neurological manifestations including pyramidal tract signs, anosmia, and ageusia. High-field MRI on T-2 weighted images of the CNS showed diffuse marginal hypointensity of the cerebrum, brain stem, and cerebellum. Atrophy of the cerebellum and brain stem was also apparent. Low signal intensity along the proximal segment of the acoustic nerve and the facial nerve was noted from the cistern to the internal auditory canal. Neither bilateral transtympanic promontory nor round window electrical stimulation elicited any sound sensation. In this case it was thought that the acoustic nerve alone or both the acoustic nerve and the cochlea were affected by this disease. Consequently, cochlear implantation was not indicated. The source of bleeding into the subarachnoid space could not be detected despite thorough examination. This diagnosis will be made only by physicians who are aware of this rare entity and have knowledge of the characteristic clinical pathology.(ABSTRACT TRUNCATED AT 250 WORDS)

Brain↗
PubMedDate not supplied

[Electrometric method of studying taste in brain diseases].

Disorders of the sense of taste were studied in 355 patients with craniocerebral pathology, among whom 70 had tumors of the acoustic nerve, 64 had a craniocerebral trauma, 60 had tumors of the cerebral hemispheres. The most coarse disorders with the loss of the sense of taste on the anterior 2/3 of the tongue were encountered in tumors of the acoustic nerve and in transverse infracture of the pyramid of the temporal bone. Longitudinal infractures of the pyramid usually cause a diminished sense of taste on the anterior 2/3 of the tongue in the acute period, with improvment of the taste in the late periods after the trauma. The test for the sense of taste on the anterior 2/3 of the tongue in tumors of the acoustic nerve, in infractures of the temporal bone pyramid, and in arachnoiditis of the cerebellopontine angle is one of the diagnostic methods. Electrogustometry makes it possible to detect the earliest disorders in the sense of taste and make a more precise diagnosis.

Arachnoiditis↗
PubMed1986

[Importance of intraoperative monitoring of ABR and compound action potential of the eighth cranial nerve during microvascular decompression surgery].

An intraoperative recording of a direct compound action potential of the 8th cranial nerve with pre, intra and postoperative monitorings of auditory brainstem evoked response (ABR) was carried out for the purpose of clarifying mechanism and prevention of postoperative hearing dysfunction following microvascular decompression surgery as a treatment for hyperdysfunction syndrome of cranial nerves. In 221 patients with hemifacial spasm and tic douloureux out of 510 patients operated on by microvascular decompression surgery, ABR was monitored before, during and after surgery and furthermore, in the recent 94 patients among them, an intraoperative direct recording of a compound action potential of the acoustic nerve was performed simultaneously. Among these 94 patients, postoperative mild hearing dysfunction was encountered in 11 patients and severe reduction of hearing acuity in 2. As a result of our studies of monitoring action potential of the 8th cranial nerve and ABR, the following conclusions were drawn. When a latency of component V of ABR was delayed by more than 1.5-2.0 msec during surgery, and delay of latency of main negative peak (N1) of an action potential of the acoustic nerve exceeded by more than 1.0 msec, the occurrence rate of postoperative hearing dysfunction became positively high. There were two different types of changes in both ABR and action potentials; one type was a delay of an action potential in combination with that of ABR latencies and the other one was merely a delay in ABR components without following a remarkable change in action potentials. The former change might due to be an insult of whole neural pathways of the 8th cranial nerve including a cochlear nucleus and the latter change may due to be functional changes of the structures proximal to the cochlear nucleus. The delay of latencies in ABR and action potentials could be imposed either by a traction of the 8th cranial nerve or by a compression of the region of cochlear nucleus by a blain spatula as well as a vascular insufficiency of the tiny vessels which supplied these neural structures. To avoid the surgical insult to the acoustic nerve itself and more proximal neural pathways, the traction of any neural structures by a brain spatula should be lasted less than 5 minutes with more than 2 minutes intervals when judged from the results of our monitoring studies and the pressure of the compression on the cerebellar cortex is much preferable to be less than 20 mmHg for the safety throughout whole surgical procedures.

Adult↗