四丘体槽くも膜囊胞の伸展方向と手術アプローチの選択

Selection of Surgical Approach for Quadrigeminal Cistern Arachnoid Cyst

Ⅰ．はじめに

　頭蓋内くも膜囊胞の発生頻度は，頭蓋内占拠性病変の約1％である¹⁾．好発部位はシルビウス裂（49％）であるが，小脳橋角部（11％）および四丘体槽部（10％）にも認められる^7,12-14)．四丘体槽くも膜囊胞の典型的な症状は，頭蓋内圧亢進症状と四丘体圧迫による眼症状であるが，中脳水道狭窄による閉塞性水頭症の原因となることもある^10,18,19)．

　くも膜囊胞に対して現在まで行われている治療法としては，囊胞腹腔短絡術と開頭による囊胞壁切除術が挙げられる．それぞれの方法には利点と問題点があり，治療方法の選択には議論の多いところであるが，囊胞が深部に存在する場合には囊胞腹腔短絡術が選択される比率が高いと報告されている¹²⁾．一方，近年の光学技術の進歩による内視鏡の細径化と内視鏡用手術器具の開発により，くも膜囊胞に対する内視鏡治療の報告が増加しており^{2-4,6,8,11,16,17)}，四丘体槽くも膜囊胞に対しても行われるようになってきた^9,15)．

　われわれは，伸展方向と症候の異なる4例の四丘体槽くも膜囊胞に対して，内視鏡単独あるいは内視鏡支援にて囊胞壁切除術を行い，良好な治療成績を得てきた．四丘体槽くも膜囊胞の伸展方向による症候の特徴と手術アプローチに関して検討したので報告する．

Preoperative magnetic resonance imaging of 4 cases of quadrigeminal cistern arachnoid cyst were retrospectively reviewed and patterns of extension to surrounding cisterns from the quadrigeminal cistern were examined. Relationship between patterns of extension to surrounding cisterns and selected surgical approach were evaluated. In 2 cases,the cyst extended anteriorly and compressed the quadrigeminal plate. These two cases had hydrocephalus due to aqueductal stenosis. The anteroirly extending cyst was treated with endoscopic ventriculocystocisternostomy via the lateral and third ventricles. In one case,the cyst extended superiorly to the velum interpositum cistern,and was treated with endoscopic ventriculocystocisternostomy via the lateral ventricle. In one case,the cyst extended laterally to the ambient cistern and compressed the posterior horn of the lateral ventricle. This case had loculated hydrocephalus of the inferior horn. The laterally extending cyst was treated with resection of the wall of the arachnoid cyst via an infratentorial supracerebellar approach assisted by endoscope. All cysts were successfully treated. Injury of the foramen of Monro occurred during a procedure using a flexible endoscope in a case with an anterior extending cyst. Exact analysis of the preoperative imaging and selection of appropriate surgical approach are key factors for successful treatment of a quadrigeminal cistern arachnoid cyst.