Direction-changing spontaneous nystagmus in cerebellopontine angle tumour.

The most common symptoms of tumours involving the cerebellopontine angle (CPA) are unilateral sensorineural hearing loss, dizziness, and asymmetric tinnitus. While the clinical manifestations have been well documented in previous studies, the nystagmus findings in these patients have not been thoroughly investigated yet. This study aimed to investigate the incidence of direction-changing spontaneous nystagmus in patients with CPA tumours, evaluate their radiologic characteristics, and gain insight into the mechanisms underlying nystagmus. Direction-changing spontaneous nystagmus was observed in 6 out of 83 patients (7%) with CPA tumours during the 7-year period. Temporal bone magnetic resonance imaging findings revealed the presence of an intrameatal mass in CPA tumours in all six patients with direction-changing spontaneous nystagmus. Vestibular schwannomas were confined within the internal auditory meatus in four patients, and petroclival meningiomas extended into the internal auditory meatus in two patients. The mechanism of direction-changing spontaneous nystagmus may be explained as paroxysmal secondary central hyperactivity in the vestibular nucleus due to the long-standing pressure effect in the vestibular nerve by tumours, or by ephaptic discharges in the vestibular nerve.