硬膜内に進展した後頭骨板間層類皮腫の1例

A Case of Occipital Diploic Dermoid Tumor with Perforation of the Dura

Ⅰ．はじめに

　類上皮腫や類皮腫はともに胎生期遺残組織の迷入が主な発生母地とされ，脳腫瘍としては比較的稀な腫瘍である．前者は上皮組織のみで囲まれ皮膚付属器を欠き，小脳橋角部や傍鞍部，頭蓋骨板間層によく認められるのに対し，後者は皮脂腺や毛髪などの皮膚付属器を有し，下垂体部や小脳虫部，脳幹，副鼻腔，眼窩などの正中線上に好発する．今回，CTおよびMRI所見より右後頭骨板間層から頭蓋内に大きく進展した類上皮腫と術前診断したものの，病理組織にて囊胞壁の一部に皮脂腺を含んでいたため類皮腫と診断された1例を経験したので，文献的考察を加え報告する．

　Along with epidermoid cysts, dermoid cysts are uncommon, benign and slow-growing lesions. We described a case of diploic dermoid cyst of the occipital bone with an intracranial extension in the right posterior fossa diagnosed and subjected to pathological examination. A 63-year-old man presented with dizziness at the time of posture conversion. Magnetic resonance imaging（MRI）showed a heterogenous hypo-intensity area on T1-weighted image, hyper-intensity on T2-weighted image and remarkably-strong intensity on diffusion-weighted image. Gadolinium enhancement was partially seen in the tumor capsule. Bone density computed tomography（CT）and 3-dimensional CT using helical CT scan revealed the osteolytic range with destruction of the inner and outer table. From these findings, this tumor was diagnosed as diploic epidermoid cyst before surgery. The tumor was totally removed and underwent cranioplasty with a titanium plate. However, pathological examination confirmed dermoid cyst with existence of sebaceous gland in some cyst-walls. It was difficult to diagnose this case as dermoid tumor from radiological features before surgery.