Abstract
Primary position upbeat spontaneous nystagmus is a sign of a central vestibular lesion, and apogeotropic positional nystagmus is rarely caused by cerebellar lesions. Low-tone sensorineural hearing loss is a symptom of endolymphatic hydrops-related disorders, such as Meniere's disease. Herein, we report a case of a tumor in the fourth ventricle who presented with primary position spontaneous upbeat nystagmus, apogeotropic positional nystagmus and low-tone sensorineural hearing loss. A 25-year-old man visited our hospital complaining of bilateral tinnitus with persistent dizziness. MRI revealed a mass in the fourth ventricle with hydrocephalus, and surgical resection of the tumor was performed. The tumor was found to arise from the pons and lower midbrain, and was diagnosed by histopathology as pilocytic astrocytoma. It is assumed that the primary position upbeat spontaneous nystagmus was caused by the tumor of the fourth ventricle affecting the region of pressure of the tumor of the fourth ventricle at the ventral tegmental tract or brachium conjunctivum in the midbrain tegmental area, and that the apogeotropic positional nystagmus was caused by the tumor compressing the cerebellum. The tumor of the fourth ventricle may also have caused obstruction of the endolymphatic sac, resulting in the endolymphatic hydrops endolymphatic hydrops could have been caused by the tumor of the fourth ventricle causing extramural obstruction of the endolymphatic sac.
