粘膜筋板の内反により深達度診断が困難であった表面型直腸粘膜内癌の1例

Flat and Depressed Type Intramucosal Carcinoma in the Rectum with Challenging Invasion Depth Diagnosis Because of Inverted Muscularis Mucosae, Report of a Case

要旨●患者は60歳代，男性．201X年盲腸癌術後のスクリーニング大腸内視鏡検査でRaに5mm大の，中央に発赤調を呈し半球状に隆起する粘膜下腫瘍様の隆起性病変を認めた．10か月後の経過検査では病変の大きさに変化はみられなかったが，中央隆起部は前回の半球状の発赤した隆起から辺縁平滑な急峻な下掘れ状陥凹へと形態変化を認めた．EUSでは低エコー腫瘤は粘膜下層3,000μmまでの浸潤所見を認め，固有筋層との間にはspaceを認めた．EUS上ではT1b癌と診断したが，病変が小さく，EUSで腫瘍と固有筋層との間にはspaceを認めたことからESDを施行し，断端陰性での一括切除が可能であった．病理組織学的には大きさ5×3mm大の0-IIa＋IIc型病変で，癌は粘膜下層には浸潤せず，粘膜筋板の内反によりSM内に押し下げるように粘膜内で増殖した高分化腺癌，pTis，ly0，v0，HM（−），VM（−）であった．

　In a male patient in his sixties, a 5-mm submucosal tumor-like lesion with reddish central protrusion was detected on colonoscopy. The 10-month follow-up colonoscopy revealed that the lesion size remained unchanged, but its shape changed to a flat elevated lesion with a central depression. Endoscopic ultrasonography revealed that hypoechoic tumor invaded the submucosal layer with 3,000-μm invasion distance, and the submucosal space was visualized between the tumor invasion front and proper muscle layer. However, the preoperative diagnosis was submucosal invasive cancer with moderate amount ; the lesion was small, and the submucosal space was visualized between the tumor invasion front and proper muscle layer by EUS. In addition, endoscopic submucosal dissection was performed, and en-block resection with negative vertical margin was accomplished. Histopathological specimens revealed well-differentiated intramucosal carcinoma（Tis）ly0, v0, HM（−）, VM（−）mimicking submucosal（T1）carcinoma because of inverted muscularis mucosae into the submucosal layer.