[Neuro-otologic diagnosis of tumors of the posterior cranial fossa--delayed auditory evoked potentials also on the opposite side].

We report on patients from a combined neurosurgical neuro-otological group (N = 36) in whom we were able to show that in tumours of the posterior cranial fossa, the acoustic evoked potentials may be -normal on the healthy side; -delayed on the healthy side, too, and improved post-operatively; -delayed on the healthy side postoperatively only. The relevant constellation of findings is mainly determined by the localization and size of the tumour, and hence by compression of the brain stem with or without occlusive hydrocephalus in the fourth ventricle. The observations suggest that mere comparison of the latency differences of both sides does not exhaust the possibilities of ERA; and, rather, that it is necessary to record the responses from both sides over the usual audiometric range of sound intensity and to correlate them both to the norm latencies and to the individual audiometric image.