殿部粉瘤から発生した扁平上皮癌の1例

Squamous Cell Carcinoma Arising in an Atheroma of Buttock. Case Report

　症例は74歳の女性で，20年前から左殿部に腫瘤を自覚していた．最近になり増大してきたため当院を受診した．MRI画像では左殿部皮下に腫瘤を認め，内部に壁から隆起するようにT1・T2強調像ともに等信号を示す疣状の充実性病変を認めた．辺縁切除後の病理検査では，この充実性部分は高分化型の扁平上皮癌であった．粉瘤悪性化の過去の報告でも，MRI画像上粉瘤内に壁から隆起するT1・T2強調画像にて等～高信号を呈し，造影効果を伴う充実性病変を認めており，このような所見は粉瘤の悪性化を示唆するものと考えられた．

　We report a case of squamous cell carcinoma (SCC) arising in an atheroma of the buttock. A 74-year-old woman first noted a mass on her left buttock 20 years previously. The mass had enlarged over the years, and she came to our hospital for a consultation. MR imaging showed a well circumscribed cyst on the buttock, and T1 and T2 weighting revealed a papilla-like solid lesion of intermediated intensity inside the cyst. Marginal excision of the cyst was performed. Histological examination revealed an epidermoid cyst and well-differentiated SCC continuous with the cyst wall. Surgery was followed by adjuvant radiation therapy, and the patient is alive without local recurrence or distant metastasis as of 11 months postoperatively. Three other case reports of SCC arising from an atheroma have described the same MR imaging findings of a well-defined solid lesion inside the cyst that was high～intermediated intensity on T1 and T2 weighting and enhanced. Such findings indicate malignant degeneration of an atheroma.