仙骨部の巨大表皮囊腫に，有棘細胞癌を合併した1例

Squamous Cell Carcinoma Arising in a Giant Epidermal Cyst. Case Report

　症例は，64歳の男性である．15年前に殿部に腫瘤が出現して，徐々に増大したため当科を受診した．MRIで，仙骨部皮下脂肪内にT1強調画像で等信号，T2強調画像で高信号を呈する多房性腫瘤を認めた．造影MRIでは被膜のみが造影された．表皮囊腫と診断して摘出術を行った．病理組織検査の結果，囊腫は増殖性表皮囊腫と外毛根鞘性囊腫からなり，増殖性表皮囊腫から連続性に有棘細胞癌が認められた．後日，追加切除と大殿筋皮弁術を行い，放射線療法を追加した．治療終了後，6カ月経過後の時点では，再発や転移はない．

　We report a case of squamous cell carcinoma arising in a giant epidermal cyst. A 64-year-old man first noticed a tumor in his right buttock 15 years before, and consulted us because it had gradually grown larger. MRI revealed multiple cysts with T1 low signals and T2 high signals. On enhanced MRI scans only the tumor sheath was enhanced. The clinical diagnosis was epidermal cyst, and surgical resection was performed. Histological examination revealed a hybrid cyst consisting of a proliferating epidermal cyst and a proliferating trichilemmal cyst. Squamous cell carcinoma was found in the proliferating epidermal cyst. Additional resection was performed, and the surgical wound was covered with a gluteus maximus flap. There have been no signs of recurrence or metastasis as of six months postoperatively.