Contribution of BERA to the Diagnosis of Neurinomas ofthe Acoustic Nerve

Overview

Neurinoma of the acoustic nerve is a tumour which attracted for several decadesattention of otorhinolaryngologists and neurosurgeons. The number of published papers on thesubjects is increasing every year. The increased interest in this tumour is conditioned by the routineuse of new examination methods in clinical practice and improving standards of the microsurgicaltechnique.Among tumours of the pontocerebellar angle the neurinoma has the closest relationship with fibresof the acoustic nerve. It is a benign tumour which originates from Schwann cells of the vestibularpart of the statoacoustic nerve. Therefore the more accurate term is vestibular schwannoma.Thesite of origin of the neurinoma is the area of the orifice of the outer auditory meatus, a site wherethe nerve is still covered by a sheath of Schwann cells.The tumour spreads at first in the directionof the inner auditory meatus and enlarges it , then it grows into the pontocerebellar angle and finallycauses compression of the brainstem. House differentiates according to the size and spread of thetumour four clinical stages of the disease.Stage I is a tumour which grows only in the inner auditorymeatus , stage II a tumour which spreads already to the area of the orifice of the inner auditorymeatus, stage III a tumour which spreads to the pontocerebellar angle, stage IV a tumour causingcompression of the brainstem. The incidence of the tumour is some nine cases per 1 millionpopulation per year, i.e. ca 0.01 pro mille.At the Clinic of Otorhinolaryngology and Surgery of the Head and Neck and Faculty Hospital, FirstMedical Faculty Charles University Prague-Motol in 1998 microsurgical operations of neurinomasof the statoacoustic nerve were introduced.Before the operations the patients were subjected to anaudiological examination. A group of 23 patients was involved with a diagnosed neurin oma confirmed histologically after operation. The patients were subjected to sound audiometry , examined bysuprathreshold tests , clinical tympanometry , incl. examination of the stapedial reflex, verbalaudiometry, examination of otoacoustic emissions and acoustically evoked brainstem pontentials.Of thr series of tests examination of acoustically evoked brainstem potentials (BERA-BrainstemEvoked Response Audiometry) proved most useful. In none of the patients a normal BERA recordwas obtained.Therefore, consistent with the majority of authors concerndc with the given problemwe consider BERA examination as one of the decisive methods for assessment of the diagnosis ofa vestibular schwannoma.In our group we did not find a statistical relationship between tumoursize and the type of record (classification of records according to Maurer). The majority of patients(78.3 %) attended examination only in stage IV of the disease. We assume therefore that the majorityof neurinomas of the acoustic nerve is diagnosed late. By detailed audiological examination of everyperception hearing disorder it would be possible to detect the disease already in earlier clinicalstages and thus improve the perspectives of the patients to preserve the function of the VIIth nerveand of the acoustic part of the VIIIth nerve.In our patients audiological symptoms predominated as the first sign of the disease over neurological symptoms (73.1 %).The presence of a statoacoustic tumour must be taken into account not only in patients withunilateral progressing perception hearing disorders associated with tinnitus but also in patientswith an atypical symptomatology ( e.g. sudden hearing disorder, sudden deterioration of an alreadyexisting perception defect, dysgeusia , neuralgia of the trigemninal nerve).The suspected presenceof a tumour is confirmed unequvically by nuclear magnetic resonance.

Key words:
BERA, neurinoma of the acoustic nerve.