Inverted Bruns' nystagmus in arachnoid cysts of the cerebellopontine angle.

A 9-year-old girl with huge, double arachnoid cysts at the cerebellopontine angle is reported. After a cyst-peritoneal shunt operation, she developed fine, high-frequency gaze nystagmus towards the lesion side combined with coarse, large amplitude nystagmus in the opposite direction, which is the reverse of the Bruns' nystagmus. We call this reverse phenomenon 'inverted' Bruns' nystagmus. As the nystagmus disappeared after a second shunt operation, the nystagmus was presumed to be caused by the cystic lesion.