非注視下において交代性眼振を呈した小脳橋角部髄膜腫症例

A Case of Cerebellopontine Angle Meningioma with Periodic Alternating Nystagmus

　I．緒言

　第1眼位で周期的に眼振の方向が左右に変換する交代性眼振は，Borries^1）の報告以来，注目されるようになり，現在まで約100例の報告があるが，その発生機序は不明である。我々は非注視下においてのみ交代性眼振を呈した右側小脳橋角部髄膜腫症例を経験したので，神経耳科学的検討を加え報告する。

　About one hundred cases of periodic alternating nystagmus (PAN) have been reported since Borries first described in 1920, although, the etiology and the pathophysiology of PAN are still undetermined. A case of cerebellopontine angle meningioma with PAN was studied neurotologically. A 38-year-old female presented chief complaints of hard of hearing and tinnitus in the right ear. The alternating nystagmus was only present when the eyes were closed or kept open in dark and disappeared with visual fixation. Caloric test showed a remarkable hypoexcitability in the right side. The function of visual fixation was preserved in this patient by visual suppression test. The alternating nystagmus disappeared soon after subtotal removal of the tumor.