Pattern visual evoked potential in patients with posteriorly situated space-occupying lesions

The potentials evoked by pattern reversal stimulation (2/sec, 11 degrees field, 26' high contrast checks) are described in 22 patients with intracranial space-occupying lesions lying posterior to the optic chiasm. Seventeen (77%) of these patients had clinically demonstrable visual field defects. The nature and position of the lesion was defined by CT scan, by cerebral angiography, or at operation. Completely normal pattern visual evoked potentials (VEPs) were recorded in four patients (18%), all of whom had full visual fields. Definitely abnormal VEPs occurred in 12 patients (55%), 11 with visual field defects. The remaining six patients (27%), all with visual field defects, had VEPs that were inconsistently abnormal and they are rated as equivocal. The findings are discussed with particular attention to the importance of stimulus and recording parameters.