長期間症状固定した視野障害，認知機能障害に対して手術が著効した成人側頭円蓋部くも膜囊胞の1例

Remarkable Recovery of Chronic Symptoms in an Adult with Middle Fossa Convexity Arachnoid Cyst after Cystoventriculostomy:A Case Report

Ⅰ．はじめに

　頭蓋内くも膜囊胞は，出生時もしくは生後間もなく形成され，多くは無症候のまま残存すると考えられ，画像検査で偶発的に発見されることも少なくない．くも膜囊胞が増大する場合はその大多数が小児期に進行し，成人期に進行することは非常に稀である^2,16)．成人期にくも膜囊胞が増大を続けたり，臨床症状を来したりするといった報告は少ない．また，成人期に軽度の症状が固定した状態で経過した後にくも膜囊胞がみつかった場合，くも膜囊胞の治療により長期固定した症状が改善する可能性の判断は困難である．くも膜囊胞に対する外科治療には少なからず合併症があることを考慮すると^5,12)，症状固定後どの程度の期間までが手術適応と判断できるかに関して，コンセンサスが得られていないのが現状である．

　成人期に側頭円蓋部くも膜囊胞を診断された後，精査にて視野欠損，認知機能障害を認め，2年の経過で軽度の左上肢麻痺が新規に出現したため新規症状改善目的にて開窓術を施行し，左上肢麻痺に加え，視野欠損，認知機能障害のすべての症状が改善した稀な症例を経験したので報告する．

　Intracranial arachnoid cysts（ACs）are thought to develop during infancy and remain clinically asymptomatic in most cases. AC is often diagnosed incidentally during imaging studies. The prognosis for the recovery of newly developed symptoms is usually favorable. However, the prognosis following surgery for chronic symptoms is still unclear. Herein, we report the case of an adult patient with right convexity AC whose chronic symptoms improved after surgery.

　The patient was a 63-year-old woman who had an AC in her right temporal convexity since the age of 59, without any symptoms, which was incidentally diagnosed on MRI. At 61 years of age, she visited a hospital complaining of slight weakness in her left upper limb. No changes were found on the MRI scan, but her visual field indicated the presence of a left homonymous hemianopia, and her cognitive function had decreased slightly. Two years later, she developed modest left hemiparesis;therefore, she underwent cystoventriculostomy to improve the symptoms of hemiparesis. After the surgery, the left hemiparesis recovered fully, and a remarkable improvement was noted in the left homonymous hemianopia and the degenerated cognitive functions.

　There are no clear guidelines regarding the surgical indications for AC in adults. Many reports suggest that new symptoms related to AC can be improved with surgery. However, amelioration of chronic symptoms has rarely been reported. The present case indicates that it is possible to improve the chronic symptoms of AC in adults with surgical procedures.