囊状変性を伴った側頭骨線維性骨異形成症の1例

A Case of Calvarial Fibrous Dysplasia Presenting with Cyst Degeneration

Ⅰ．はじめに

　線維性骨異形成症（fibrous dysplasia：FD）は頭蓋顔面骨に発生する最も一般的な良性腫瘍である．正常骨髄が徐々に異常な線維性結合織に置き換わっていく結果，FDが形成されると考えられているが，その成因は不明である．FDは臨床上単一骨を侵し全体の多くを占めるmonostotic formと，複数骨を障害し稀なpolyostotic formに分類されている¹⁾．頭蓋顔面骨FDに最も頻度の高い臨床所見は顔面の非対称（86％）である．前頭骨が最も障害されやすく，次いで蝶形骨が侵されやすい⁸⁾．脳神経に対する圧排，伸展，絞扼などによる各種脳神経症状，美容面での問題を生じ得るが，一般に手術成績は良好である⁷⁾．約0.5％で悪性転化するが，その多くはMcCune-Albright症候群と関連したpolyostotic formに起こると考えられている¹⁾．無症候性のFDが経過中に囊状変性（cyst degeneration）を起こし急激発症することがあるが，頭蓋骨での報告は稀である¹⁾．囊状変性を起こしたFDの場合，巨細胞腫，軟骨芽細胞腫，血管腫，動脈瘤様骨囊腫などとの鑑別が問題となる^2-5)．今回われわれは囊状変性を来し痛みで発症した前頭骨monostotic FDの症例を経験したので，発症機序の考察を含め報告する．

　A 49-year-old female developed a painful dysesthesia in the left forehead 10 years after having become aware of a subcutaneous mass accompanied with mild tenderness. Her medical history was unremarkable. Neurological examination showed normal findings with intact facial nerve function. Blood examination was normal. Neuroimaging revealed a cystic bony mass and an adjacent patchy diploic lesion in the left temporal bone. She underwent total tumor resection by frontotemporal craniotomy. Intraoperatively,a bony defect was noted in the lower surface of the patchy lesion communicating with the diploic venous system. A part of the dura mater was invaginated in the bony defect. The patchy lesion was found to communicate with the bony cyst through the diploic structure. Histological appearance of the bony cyst was consistent with the fibrous dysplasia accompanying cyst degeneration. Histological findings of the patchy lesion were identical to those of the bony cyst except for cyst degeneration. We assumed that the diploic venous system and the meningeal vessel might have been associated with the etiology of cyst degeneration in the present case of fibrous dysplasia.