Bruns Nystagmus (During Video-Oculography) Due to Vestibular Schwannoma

A 25-year-old man with a history of right-sided hearing loss, headaches and imbalance was found to have a right vestibular schwannoma on MRI, and underwent a partial resection and radiotherapy. He denied symptoms of head movement dependent oscillopsia (i.e., suggestive of significant unilateral or bilateral vestibular loss), but did experience oscillopsia when looking to the right (absent head movement). With fixation, there was subtle spontaneous left-beating nystagmus (LBN) in primary position and in up and down gaze, increasing in left gaze in accordance with Alexander's law, consistent with vestibular nystagmus due to the right vestibulopathy (from the schwannoma). This vestibular nystagmus was high frequency and small amplitude. In right gaze, there was low frequency, large amplitude right-beating nystagmus (RBN), consistent with gaze-evoked nystagmus due to dysfunction of the gaze-holding mechanism (neural integrator) from right posterior fossa compression (especially the cerebellar flocculus based on MRI). The combination of contralesional (LBN) vestibular nystagmus and ipsilesional (RBN) gaze-evoked nystagmus is characteristic of cerebellopontine angle pathology, and is termed Bruns nystagmus. 1