Auditory brain stem responses in patients with posterior fossa tumors.

Twenty patients suffering from space-occupying lesions of the posterior fossa were investigated with the help of brain stem auditory evoked potentials. The results were compared with the findings of computerized tomography (CT) and with the operative findings. In large cerebellopontine angle tumors, there was severe attenuation of all components ipsilateral to the lesion, which may or may not include wave I. In patients with intrinsic pontine tumors, severe degradation of the components subsequent to wave III was found. In cerebellar tumors, caudal distortion of the brain stem seems to cause an increase of the interpeak separation of III-V, whereas rostral compression did not alter the responses. No consistent pattern appears to be recorded in extrinsic brain stem tumors. In only 2 of 8 patients in whom postoperative observations were made did the postoperative responses parallel the overall clinical course of the early postoperative period.