深達度診断に苦慮した横行結腸早期癌の1例

Early Transeverse Colon Carcinoma which was Difficult to Diagnose

要旨　患者は50歳代，女性．排便時の血液付着を主訴に当科を受診した．大腸内視鏡検査で横行結腸に径10mm大で，陥凹の中心にドーム状隆起を伴う，いわゆるIs＋IIc型病変を認めた．NBI観察では，佐野分類でIIIA，広島分類でC1，昭和分類でirregularと診断した．ピオクタニンによる拡大観察では，pitの大小不同は認めたものの，辺縁不整，内腔狭小はあまり認めず，V_I型軽度不整と診断した．超音波内視鏡では，隆起部で第3層の不整を認め，中心に低エコー領域があり，粘液や血管の存在が疑われた．以上の所見よりpSM-m癌を疑い，腹腔鏡下横行結腸切除術を施行した．病理組織学的には，粘膜内に限局した病変で，粘膜下層には動脈を主体とする大型血管の集簇を認めた．最終診断はwell differentiated adenocarcinoma（tub1），pM，ly0，v0で，リンパ節転移，遠隔転移は認めなかった．陥凹型早期大腸癌はSM浸潤率が隆起型に比較して高く，特に陥凹内隆起を伴う病変はSM深部浸潤を示唆する所見として重要とされている．今回，陥凹内に隆起を伴うが，組織学的にはM癌であった症例を経験したので報告した．

　A female over 50 years of age was referred to our department for further examination because of positive occult blood in her feceas. Total colonoscopy demonstrated a protruded lesion with a surrounding depressed part in the transverse colon. Usually, this morphological type has been classified a type Is＋IIc. NBI（narrow band imaging）observation revealed Sano's type IIIA, Hiroshima's type C1 and Showa's irregular surface vascular pattern which means mucosal carcinoma. Magnifying observation with crystal violet dyeing showed V_I mild irregular pit pattern consisting of oval long pit and small pit. In ultrasonic endscopy, the tumor's low echoic area, which was suspected as a mucinous lesion or blood vessels, invading the submucosal layer. On a whole, we diagnosed this lesion as early colonic caricinoma which had invaded at least to the mid-submucosal layer. We operated laparoscopy-assisted partial transverse colectomy. Histopathological examination revealed well differentiated mucosal adenocarcinoma（tub1）, pM, ly0, v0 with no metastasis but having a submucosal large artery.

　This case was thought to be uncommon as regards the submucosal large artery and mucosal type Is＋IIc carcinoma which had invaded the deep subumucosal layer.