Oculomotor Abnormalities in Large Cerebellopontine Angle Tumors: A Case Series of Bruns’ Nystagmus

Patients with large or giant large cerebellopontine angle lesions can present with a wide range of audiovestibular symptoms, including Bruns' nystagmus. This is a rare variant of bidirectional nystagmus, characterized by a combination of slow, large- amplitude nystagmus when looking to the side of the lesion and rapid small-amplitude nystagmus when looking to the contralateral side. This phenomenon arises due to a unique situation in which 2 different neural circuits, specifically the floccular pathways and peripheral vestibular pathways, are simultaneously involved. The presence of Bruns' nystagmus is a good indicator for large CPA lesions of at least 3 cm in diameter with compression and displacement of the cerebellum, comprising the flocculus, and/or the brainstem. A case series of 4 different cases illustrates that investigating the presence of such nystagmus could be incorporated into the common diagnostic work-up of CPA lesions, since it is of particular interest in localizing large CPA tumors requiring urgent imaging. Keywords: Brainstem, cerebellum, neurilemmoma, pathologic nystagmus, vertigo