[Auditory-evoked brainstem response in a schwannoma of the VIIIth cranial nerve: an anatomophysiological and functional correlation. Our experience].

INTRODUCTION: Schwannomas are tumors charasteristically originated from the nerve sheath. They expande eccentrically from the nerve promoting a disturbance in the neural function either due to vascular compresion or to the effect of the tumor itself on the nerve, disturbance that can be evidenced with the Auditory-evoked Brainstem Response (ABR), fact that constituted the base for their diagnosis in the past. The new radiological techniques developed over the last decades have made possible an earlier diagnosis, and therefore changed their prognosis in terms of nerve function. Diagnosis is more certain today with these techniques so it could seem that ABR may not have any longer a role in the management of this condition.

OBJECTIVE: To describe the most frequent ABR patterns in those patients suffering from acoustic schwannoma related to the size of the tumour and the remanent audition thresholds, and to determine the value of this test in our practice.

MATERIAL AND METHODS: We describe the ABR features found in our series of 72 patients. Whose diagnosis was done between 1997 and 2003 in relation to the size of the tumour and the residual auditory function.

RESULTS AND CONCLUSIONS: ABR has a good sensibility for detection of acoustic schwannoma. This sensibility decreases in small-sized tumours, specially in intracanalicular ones. ABR patterns do not relate to the size of the tumour but they do to the auditory function. The authors defend ABR to be a very valuable test due to the information and accesibility they provide.