自然消失した中頭蓋窩クモ膜嚢胞の1例

Spontaneous Disappearance of a Middle Fossa Arachnoid Cyst : A Case Report

　自然消失した中頭蓋窩クモ膜嚢胞の1例について報告する。症例は16歳の男性で，交通事故により頭部を打撲した。頸部痛のほかは神経学的異常は認めず，CTscanでは左シルビウス裂にクモ膜嚢胞が見られたが経過観察とした。10カ月後にCTscanを再検したところクモ膜嚢胞が消失し，mass effectが軽減しているのが認められた。この間に患者は更なる頭部外傷や体調の異常を自覚することはなかったことから自然消失したものと考えた。

　クモ膜嚢胞の自然消失はこれまでに4例が報告されているのみである。自然消失の機序は嚢胞の内膜あるいは外膜が破綻して内容液が吸収されたためと考えられた。

A case of a middle fossa arachnoid cyst which spontaneously disappeared is reported.

A 16 year old boy visited our out-patient clinic complaining of headache after a blunt head trauma by a motorcycle accident. The neurological exami-nation was negative except for mild neck pain on the flexion and extension of neck. Plain x-ray of skull and neck were negative. CT scan demonstrat-ed an arachnoid cyst in the left Sylvian fissure. It was planned to follow up the patient by CT scan. After 10 months, he was examined by CT scan, which revealed the spontaneous disappearance of the arachnoid cyst and some dilatation of the ante-rior horn of the lateral ventricle. The patient did not have any additional trauma or infection during the interval between two examinations.

Spontaneous disappearance of arachnoid cyst was extremely rare as only 4 cases were reported previ-ously. The basic mechanism of this natural cure was considered to be rupture of outer or inner membrane of arachoid cyst which would facilitate absorption of its content.