Effect of CSF shunt on brainstem auditory evoked potential in hydrocephalus secondary to brain tumour.

BAEPs were prospectively studied in thirty patients with hydrocephalus prior to and within 48 hours of CSF diversion. They comprised patients with (1) cerebellar tumours (2) brainstem tumours (3) third ventricular tumours. Preshunt BAEPs were abnormal in 80% patients with cerebellar tumour, 70% patients with third ventricular tumour and in all patients with brainstem tumour. Postshunt BAEPs improved in 70% patients with brainstem tumour and in 40% patients with third ventricular tumours. In both the groups I-III and III-V interpeak latency improved. In group 1, (cerebellar tumours) none of the patients showed improvement in the BAEP after shunt. In 7 patients of this group CCT deteriorated after the shunt. The deterioration was at the III-V interlatency in 5 patients. One patient had deteriorated at both I-III and III-V levels and another had prolongation of the I-III interlatency after shunting. In 6 patients the wave V amplitude reduced by more than 50% after shunting.