有茎性の直腸悪性黒色腫の1例

Pedunculated Malignant Melanoma of the Rectum, Report of a Case

要旨　症例は73歳，男性．内痔核として近医にて治療中，下血を契機に肛門縁より5cmの位置に肛門より脱出を繰り返す有茎性のポリープを発見された．二度の生検の後，内視鏡的治療の目的で紹介された．初回の生検では直腸潰瘍，第2回は低分化腺癌と診断されていたが，特徴的な内視鏡的色調から悪性黒色腫を疑った．HMB-45，S-100の免疫染色が陽性であり，悪性黒色腫と診断した．CT，MRIで直腸傍リンパ節，左閉鎖リンパ節の転移を認め，MRIのT1強調像で高信号を呈し，メラニン含有を示唆する所見であった．Miles' operationが施行され，深達度mp，リンパ管侵襲ly3の悪性黒色腫で第2群リンパ節転移陽性であった．肛門部の腫瘍性疾患の診療には悪性黒色腫を考慮することが重要と考えられた．

　A 73-year-old man was referred to our hospital for endoscopic treatment of a rectal tumor. During treatment for internal hemorrhoids, he was discovered to have a pedunculated polyp 5 cm oral from the anal verge. Biopsy had been performed twice. The first biopsy was diagnosed as rectal ulcer and the second as poorly differentiated adenocarcinoma. However, we suspected a malignant melanoma from the characteristic black color apparent during colonoscopic examination. The third biopsy specimen stained positive for Fontana-Masson, HMB-45 and S-100, so we diagnosed it as a malignant melanoma. CT and MRI disclosed swelling of the pararectal and left obturator lymph node. The rectal lesion and these lymph nodes were indicated by a high signal on the T1-weighted image of MRI, evidence suggestive of a melanin component.

　Miles' operation was performed and the tumor was 4 cm in diameter, located just above the dentate line and histopathologically diagnosed to be a malignant melanoma with a depth of invasion to mp, ly3, n2(＋).

　This case was thought to be important for indicating the possibility of malignant melanoma as a tumor located in the anorectal region.