Auditory brainstem evoked responses in brainstem compression due to posterior fossa tumors

Five patients with unilateral posterior fossa tumors were investigated with Auditory Brainstem Evoked Responses (B.E.R.). The B.E.R., recorded from the ear ipsilateral to the tumor, were consistent with a lesion of the acoustic nerve or the cochlear nuclei in all patients. The contralaterally evoked responses in four patients with large tumors and radiological signs of brainstem compression showed normal latencies and amplitudes of the first three waves, while waves IV and V were definitely abnormal with respect to amplitudes and latencies. (The 4th patient had a normal wave IV and a delayed, small wave V). In one patient with a relatively small acoustic neurinoma the contralateral B.E.R. were normal. It is concluded that the upper pontine and lower midbrain level, presumed sites of generation of wave IV and V of the B.E.R., are more susceptible to brainstem compression due to unilateral posterior fossa tumors, than the lower parts of the brainstem.