短期間にⅠs型からⅡa＋Ⅱc型へと肉眼形態が変化したS状結腸sm癌の1例

Submucosal Cancer of the Sigmoid Colon Rapidly Transforming from Sessile (Is Type) to Superficial Depressed Lesion (IIa＋IIc Type), Report of a Case

要旨　患者は49歳，女性大腸癌検診で便潜血反応陽性を指摘され，当センター外来を受診した．大腸内視鏡検査を施行したところS状結腸に大きさ約10mmのⅠs型癌を認め，形態からsm深部浸潤により隆起が形成された病変と診断した．30日後に施行した大腸内視鏡検査では，同病変は類円形の平坦な病変となり，病変中央の隆起は消失していた．隆起が消失した部分には白苔を伴った不整形の浅い陥凹とわずかな陥凹内隆起を認め，これらの内視鏡所見から病変はsmに深部浸潤したⅡa＋Ⅱc型癌と診断した．注腸X線検査では，病変は大きさ10mmの辺縁平滑な類円形病変として描出され，中央には不整形の浅い陥凹と陥凹内隆起を示す透亮像を認めた．側面像ではゆるやかな弧状変形がみられた．超音波細径プローブ所見を加味し，病変は中央部分でsmに深部浸潤したⅡa＋Ⅱc型癌と最終診断した．腹腔鏡補助下にS状結腸切除術を施行した．病理組織学的には大きさ8mmの類円形を呈する陥凹性病変で，中央の陥凹内隆起部分で深達度sm₃まで浸潤した高分化腺癌であった．病変の立ち上がり部分は正常粘膜で被覆されていた．大腸癌の発育進展を考えるうえで興味ある症例と思われ報告した．

　A 49-year-old woman was referred to our center for positive fecal occult blood. Colonoscopic examination revealed a sessile lesion (Is type), approximately 10 mm in size, in the sigmoid colon. Morphologically, it was considered to be an elevated lesion due to massive submucosal invasion. Colonoscopic examination 30 days later revealed that the lesion had metamorphosed to a flat lesion with disappearance of the elevation in the center. In the area where the elevation had disappeared, an irregular shallow depression with uneven surface was observed.

　From these colonoscopic findings, it was diagnosed as a superficial depressed cancer (IIa＋IIc type) with massive submucosal invasion. Barium enema radiograph revealed a round radiolucent lesion with a thin, irregular barium collection in the center, 10 mm in size. The profile view showed a semilunar deformity. From these findings combined with high-frequency ultra-sound probe findings, the lesion was finally diagnosed as IIa＋IIc type cancer with massive submucosal invasion at the center. Laparoscopic sigmoidectomy was perfomed. In the resected specimen, there was a IIa＋IIc type lesion measuring 8×8 mm in size.

　Histologically, it was a well differentiated adenocarcinoma with massive submucosal invasion at the center.

　The tumor border was covered with normal mucosa. The case was thought to be noteworthy for considering the natural course of colorectal cancer.