Bruns bidirectional nystagmus in cerebellopontine angle tumours.

Bruns nystagmus is an uncommon, bidirectional optokinetic disturbance associated with advanced cerebellopontine angle tumours. In a retrospective analysis of 115 such tumours, Bruns nystagmus was observed in 18 patients (16%). All tumours in this group were 3 cm or greater in diameter. Fourth ventricle displacement as assessed by computerized cranial tomography was present in all cases where the fourth ventricle was visualized (89%). Seven of 15 cases (47%) had significant contralateral N5 delay on brainstem auditory evoked potential testing, 5 (33%) were normal and 3 (20%) gave no consistent result. It was concluded that Bruns nystagmus occurs in large tumours associated with significant brainstem distortion. The neurophysiological abnormalities demonstrated by brainstem audiometry appear to be a less sensitive measure of brainstem compression than neuro-anatomical assessment using CT.