粘液結節の成分によりmpまで浸潤を認めたIIa＋IIc類似進行大腸癌の1例

Advanced Colon Cancer Resembling Type IIa＋IIc with Mucinous Component Invading the MP, Report of a Case

　症例は72歳，男性．6年前に胃癌のため胃全摘術を受けている．消化管検診の目的で受診，注腸X線検査にてS状結腸にひだ集中を伴い中央に浅い陥凹のある最大径15mmのIIa＋IIc型病変を認めた．大腸内視鏡では，立ち上がりはなだらかで，色素撒布により陥凹境界はより明瞭となったが，陥凹面での色素の付着性は不良であった．拡大内視鏡では基部から陥凹辺縁までI型pitで，陥凹内はⅤI型pit，軽度不整であった．超音波内視鏡では第3層に低エコーと結節状の無エコーが混在し，第4層を高度に圧排しており，mpまでの浸潤を疑う所見であった．生検では高分化型腺癌であり，S状結腸切除とD1郭清とした．病理組織診断は粘液結節を伴った高分化型腺癌で深達度mpであり，隆起の主な成因は粘液結節成分であり，結節の最深部でmpに達していた．本症例は早期癌としての形態を保っており，大腸粘液癌の初期像とも考えられた．表面構造が比較的保たれたまま深部への浸潤を認めた癌であり，大腸癌の深達度診断を進めるうえで極めて興味深い症例であった．

　The present case involved a 72-year-old male patient who requested a gastrointestinal examination six years after a gastric cancer procedure. A barium enema study revealed a Type IIa＋IIc lesion measuring 15 mm in maximal diameter with converging folds in the sigmoid colon. Colonoscopy showed the lesion had the same general coloring as surrounding tissue and a gently sloping base. A dye-spreading study clearly delineated the borders of the depressed region but the adherence of the indigo carmine was comparatively poor. Magnifying colonoscopy showed Type VI pit pattern with mild irregularities in the depressed area, and Type I pit pattern from the edge of the lesion to the depressed border. Ultrasonic endoscopy showed echo-free nodules and low echoic areas in the third layer, significantly suppressed in the upper part of the fourth layer. Based on these findings, we determined that the lesion invasion extended to the muscularis propria (MP) layer. Since the biopsy samples indicated well-differentiated adenocarcinoma, we performed a sigmoidectomy and D1 resection. Histological examination of resected specimens also showed well-differentiated adenocarcinoma with mucinous components and confirmed that the invasion depth extended to the MP. The lesion exhibited the configuration of early-stage colonic cancer, and the study images obtained appeared to indicate mucinous carcinoma of the colon. Since cases of invasive cancer generally retain little of the surface structure, this case was particularly interesting given the depth of invasion of the colonic cancer.