Diagnosis Of Acoustic Neurinoma Research Articles

Auditory Evoked Potentials

This article describes the basic elements of auditory evoked potentials, including stimulus tone and recording condition, and clinical applications of auditory evoked potentials, such as ECochG, ABR and ASSR. The clinical applications of auditory evoked potentials are roughly classified into (1) objective audiometry and (2) neurological examination. ECochG is applied to the diagnosis of endolymphatic hydrops and inner ear hearing loss. ABR is still an important examination in the diagnosis of acoustic neurinoma, though the prevalence of MRI has reduced its importance. The elongation of the I-V inter-peak latency (I-V IPL) of ABR in lower brainstem lesion is mainly due to I-III IPL elongation, whereas I-V IPL elongation is mainly due to III-V IPL elongation in upper brainstem lesions. Recruitment and conductive hearing loss can be estimated by the finding of the latency-intensity curve of wave V. Although ABR is the most popular device in objective audiometry, the prediction of hearing levels in the lower frequency range using ABR evoked by clicks is less accurate. The most important benefit of ASSR is to provide an accurate assessment of hearing at different frequencies in a frequency specific manner, if stimulation consists of a sinusoidally amplitude-modulated tone. However, ASSR is not appropriate to use as a diagnostic tool in neurological examinations, because the waveforms of ASSR consist of the interference of different wave components. Power spectrum analysis and phase coherence using fast Fourier transformation are useful for the automatic detection of ASSR, because of its sinusoidal waveform configuration. Because the detectability of ASSR changes under different arousal states, 40-Hz ASSR is suitable for waking adults and 80-Hz ASSR for sleeping children in the assessment of hearing. Its advantage is that the thresholds at 4 different frequencies in both ears can be predicted more rapidly than ABR using the multiple simultaneous stimulation technique.

Evaluation of the vestibulo-ocular reflex using sinusoidal off-vertical axis rotation in patients with acoustic neurinoma

The vestibulo-ocular reflex (VOR) was studied to examine the utility of off-vertical axis rotation (OVAR) in the diagnosis of acoustic neurinoma. Subjects were sinusoidally rotated with eyes open in complete darkness at frequencies of 0.4 and 0.8 Hz with a maximum angular velocity of 60°/s at either earth-vertical axis rotation (EVAR) or OVAR. Thirteen patients with acoustic neurinomas were investigated. Results showed that VOR gain during OVAR at 0.8 Hz and in a 30° nose-up position in patients with internal auditory canal tumors was significantly less than the gain measured during EVAR. The VOR gain measured from all patients (including those with tumors extending to the cerebellopontine angle) was not significantly different when the patients were subjected to EVAR and OVAR. These observations were possibly due to superior vestibular nerve dysfunction. We concluded that certain stimulating parameters—patient's nose tilted up 30°; sinusoidal OVAR at 0.8 Hz and 60°/s maximum angular head velocity—were useful for evaluating vestibular function in patients suffering from an acoustic neurinoma located within the internal auditory canal.

Surdez súbita unilateral como manifestação de schwannoma vestibular: relato de caso

O schwannoma vestibular, também conhecido como neuroma ou neurinoma do acústico, é o tumor mais freqüente do ângulo pontocerebelar correspondendo a aproximadamente a 9% de todos os tumores intracranianos. APRESENTAÇÃO DO CASO: Os autores apresentam um relato de caso de surdez súbita e zumbido unilateral com melhora dos sintomas através de tratamento clínico com Prednisona e Pentoxifilina e posterior diagnóstico por exame de imagem de schwannoma vestibular. DISCUSSÃO: A surdez súbita pode ser descrita como uma perda neurossensorial abrupta e intensa. Costuma ser acima de 30 dB, em três ou mais freqüências contíguas e se desenvolve em menos de três dias. CONCLUSÃO: É de grande importância a pesquisa da etiologia nos casos de surdez súbita para a boa condução do caso e orientação terapêutica.

Facial nerve involvement in patients with acoustic neurinomas. Examination with magnetic single- and bi-stimulation.

The diagnosis of acoustic neurinomas is usually made by auditory and vestibular testing and magnetic resonance imaging. As clinical involvement of the facial nerve is infrequent, occurring only in large tumours, only little is known about the subclinical involvement of the facial nerve. Transcranial magnetic stimulation of the VIIth cranial nerve in the temporal bone, adjacent to acoustic neurinoma growth, seems to be an adequate instrument for electrophysiological measurements of minimal nerve lesions without clinically obvious facial palsy. In 70% out of 97 patients with surgically and histologically confirmed acoustic neurinomas, obvious elongation of the intratemporal conduction time of the facial nerve was found. This affection was dependent on tumour size. No correlation was found to preoperative or postoperative facial nerve function and hearing function. The latencies of the conduction time showed a tendential increase in patients with a more difficult grade of surgery and of facial nerve preparation due to fibrous adhesions and nerve spreading on the tumour capsule. A completely new stimulation modality, the application of two magnetic stimuli in quick succession, was applied for the first time in acoustic neurinoma patients, and revealed facial nerve involvement by acoustic neurinoma growth. Facial nerve involvement in acoustic neurinoma can be detected by transcranial magnetic stimulation even in patients with small and medium sized tumours but with clinically normal facial function.

Diagnosis of acoustic neurinoma in its early stages

Diagnosis of acoustic neurinoma in its early stages

False‐positive MR imaging in the diagnosis of acoustic neurinomas

False‐positive MR imaging in the diagnosis of acoustic neurinomas

聴神経腫よう診断への耳鼻咽喉科医の寄与 全国大学附属病院調査

In order to find out how otologists contribute to the diagnosis of acoustic neurinoma, a questionnaire was sent to 80 neurosurgical departments of university hospitals. Answers were obtained from 71 departments.1) Acoustic neurinomas represented 7.8% of all brain tumors in Japan. The rate varied from 0% to 24% in university hospitals. 2) 48.8% of acoustic neurinomas were diagnosed by otologists. The rate varied from 0% to 100% in university hospitals.Since in most cases, the first symptom of acoustic neurinoma is unilateal progressive hearing loss, it was presumed that more than 48.8% of acoustic neurinoma patients had visited an otologist's clinic.In order to prevent wrong diagnosis, problems which frequently rise in diagnosing acoustic neurinomas are discussed.

Clinical aspects and diagnosis of acoustic neurinomas

The application of microsurgical techniques for the removal of acoustic neuromas has evidenced greatly improved postoperative results. Therefore the early detection of an acoustic neuroma is a special need for every neurologist. The development of new electrophysiological and radiological procedures now allows a far better approach in the diagnosis of acoustic neuromas. Brain stem auditory evoked potentials as well as acoustic reflex testing have shown to be rather sensitive tools in the diagnosis of retrocochlear pathology. Other electrophysiological procedures have been widely replaced by these techniques. Gasmeatocisternography in combination with cranial computed tomography is the method of choice in the detection of small acoustic neuromas. The current status in the application of different techniques for the diagnosis of acoustic neuromas is reviewed.

Stapedius reflex test, brainstem audiometry and opto-vestibular tests in diagnosis of acoustic neurinomas. A comparison of test sensitivity in patients with moderate hearing loss.

The stapedius reflex test, brainstem audiometry and the opto-vestibular tests for identifying acoustic neurinomas (AN) were evaluated and compared in a study of 21 patients with radiologically or surgically verified AN and a pure tone average not exceeding 60 dB HL. The stapedius reflex test results were interpreted according to the criteria developed at this clinic. The stimuli for the auditory brainstem response (ABR) were 2 kHz haversine waves and 4 kHz square waves. The vestibular examination consisted of a caloric test and the recording of eye-tracking and gaze nystagmus. In the cases studied the stapedius reflex test gave 1 false-negative result and ABR none. The ENG gave 3 false-negatives whereas the results of speech discrimination tests were misleading in no fewer than 1/3 of the cases. The results of the different tests were directly correlated but correlation coefficients did not exceed 0.65. Tumours larger than 15-20 mm showed a different test pattern than those below that size: stapedius reflex response, ABR and caloric response were eliminated and all of these patients had abnormal optomotor function. It is suggested that an optimal routine test procedure should consist of a pure tone audiogram, supplemented by ABR or the stapedius reflex test. Opto-vestibular tests may be of value in a preliminary estimation of tumour size.

Differential diagnosis of acoustic neurinomas.

Differential diagnosis of acoustic neurinomas.

Computed Cranial Tomography in Acoustic Tumor Diagnosis

With the development of computed cranial tomography (CCT), many physicians have come to rely on this technique as their sole means of excluding a diagnosis of acoustic neurinoma. In our series of 237 patients with acoustic tumors, 29% of tumors were not detected by CCT. New thin-section scanners improve this detection rate. Tumors within the internal auditory canal, however, will not be detected without special techniques. We recommend that contrast studies of the posterior fossa be employed to exclude definitely the diagnosis of acoustic tumor when one is suspected.

The surgical management of acoustic neurinomas

SummaryAcoustic neurinoma must be included in the differential diagnosis of vertigo. With present audiometric, vestibular and radiographic tests, the diagnosis of acoustic neurinomas may be established with a high degree of certainty. Diagnosis and management of these tumours are discussed.

M�glichkeiten der otoneurologischen Diagnostik mit Hilfe der trigemino-facialen Reflexe

The central transfer of the trigemino-facial reflexes (TFR) from the afferent to the efferent part takes place at the pons level as well as in higher cerebral regions. TFR can therefore be employed as a supplementary topodiagnostic aid in several diseases with central-nervous manifestation. Since the reflex-conducting motoneurones of the N. facialis are especially sensitive to pressure, lag time delay and amplitude suppression of the TFR are particularly sensitive indicators of a developing neurapaxia. TFR registration therefore seems to be especially suitable for an early diagnosis of acoustic neurinomas. The method is characterized by the special possibility of directly investigating the affected part of the nerve. For the different places of damage: N. trigeminus, brain stem and N. facialis, clinical examples are given.

The diagnosis of acoustic neurinoma. A retrospective study.

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Angiographic diagnosis of acoustic neurinomas: analysis of 30 lesions.

Vertebral angiograms in 30 surgically proven acoustic neurinomas are reviewed and arterial and venous abnormalities are analyzed in detail. Previously described angiographic abnormalities are confirmed including displacement and non-visualization of the anterior inferior cerebellar artery and the petrosal veins. In addition arched displacement of the superior cerebellar artery and the marginal artery is emphasized as an important finding in these tumours. Description is given of an abnormal vein which is enlarged and displaced posteriorly in an arcuate fashion over the mass. This unnamed abnormal vein offers one of the most important findings in the diagnosis of acoustic neurinomas. It is concluded that acoustic neurinomas of more than 2.0 cm in diameter can be diagnosed accurately by vertebral angiography and important additional information for surgical removal can be obtained.

The value of the subtraction method in the diagnosis of acoustic neurinomas.

The value of the subtraction method in the diagnosis of acoustic neurinomas.

Diagnosis of acoustic neurinoma by pneumoencephalo-roulette tomography. Technical note.

Diagnosis of acoustic neurinoma by pneumoencephalo-roulette tomography. Technical note.

The otoneurological diagnosis of intracranial expansive processes.

A total of 187 patients with a suspected intracranial expansive process were studied at the Otolaryngological Hospital, University of Helsinki, in co-operation with the Department of Neurosurgery. After a complete otoneurological and neurosurgical examination 126 of them were found to have an expansive process. The involvement could be neither excluded nor confirmed with certainty in 13 cases, and in 48 the possibility of an expansion was excluded completely. The material included 58 acoustic neurinomas, 52 of which were verified histologically. The otoneurological finding supported the diagnosis of acoustic neurinoma in 53 (91 per cent) cases. In the other cases of expansive processes of the posterior fossa, 2(5 out of 39 (67 per cent) displayed symptoms suggestive of expansion of the posterior fossa. Otoneurological symptoms indicative of expansion were established in 8 (28 per cent) out of 29 cases with an expansive process external to the posterior fossa.An der Universitats-Ohrenklinik des Zentralkran...