Electronystagmographic findings in 147 patients with acoustic neuroma.

We report on the preoperative findings in 147 patients with surgically confirmed acoustic neuroma (AN). Gaze nystagmus, spontaneous nystagmus and positional nystagmus were present in 23.1%, 47.5% and 63.0% of the patient, respectively. Pathological findings in ETT, OKP and bithermal caloric test were found in 44.3%, 45.3% and 77.0%, respectively. The ratio of pathological findings in ETT and OKP was larger in the large tumor group than in the small tumor group. Gaze nystagmus to both directions and direction-changing positional nystagmus were also found in the large tumor group. While the correlation between tumor size and CP% in caloric test was slightly significant (correlation coefficient, 0.52) in all 122 patients, it was more significant (correlation coefficient, 0.65) in 16 patients whose tumor origin was surgically confirmed to be the inferior vestibular nerve. These findings suggest that reduced caloric response is caused by compression of the nerve by tumor mass. On the other hand, 6 patients whose tumor originated from the superior vestibular nerve showed no significant correlation between CP% and tumor size.