過形成，鋸歯状腺腫から発育進展した大腸低分化腺癌の1例

Colonic Poorly Differentiated Adenocarcinoma Developing from Hyperplastic and Serrated Adenoma, Report of a Case

要旨　患者は30歳代，男性．健診で腫瘍マーカー（CA19-9）の高値を指摘され，精査目的で当センターを受診した．大腸内視鏡検査で，横行結腸肝彎曲部に，大きさ約20mmのI＋IIa＋IIc病変を認め，その周囲に粘膜下腫瘍様の盛り上がりとリンパ濾胞の過形成を伴っていた．拡大内視鏡検査では，IIa部分は過形成，I部分は鋸歯状腺腫で，IIc部分はV_I～V_N型pit patternを呈していたため，SM浸潤癌と診断した．注腸X線検査では，病変周囲の粘膜下腫瘍様隆起が明瞭に病出されており，側面像でも硬化所見を認めたことから，鋸歯状腺腫を伴ったSM深部浸潤癌と診断し，右半結腸切除術を施行した．病理組織学的所見では，隆起部は過形成粘膜，鋸歯状腺腫，管状腺癌から成り，陥凹部は低分化腺癌がSM深部浸潤を来し，高度なリンパ管侵襲とリンパ行性の進展が粘膜下腫瘍様隆起を形成していた，さらに漿膜および上腸間膜にリンパ節転移を認めた．以上から，本症例は，過形成粘膜から鋸歯状腺腫が発生し，異型度を増しながら管状腺癌，低分化腺癌へと発育し，リンパ行性の進展と高度なリンパ節転移を来したと推測され，その特異的な発育進展を推測できる特徴的な画像所見が得られたので報告した．

　A 3x-year-old man was referred to our hospital because of high levels of the tumor marker CA19-9 identified at an annual health check-up. Colonoscopy revealed a type I＋IIa＋IIc lesion 20mm in diameter with surrounding submucosal tumor-like protrusion and lymphoid follicle hyperplasia at the hepatic flexure of the transverse colon. This lesion was diagnosed as submucosal（SM）invasive carcinoma, as magnifying colonoscopy indicated a hyperplastic pattern for IIa lesion, serrated adenoma for I, Vi and Vn pit pattern for IIc. As double-contrast barium enema examination depicted a distinct submucosal tumor-like protrusion with an indurated layer in lateral view, a diagnosis of SM invasive carcinoma with serrated adenoma was made. Consequently, right hemicolectomy was performed. Histopathological study indicated hyperplastic serrated adenoma and tubular adenocarcinoma for the protruding lesion, and poorly differentiated adenocarcinoma with severe SM invasion for the recessed lesion. Severe lymph duct invasion and lymph node progress were observed within the submucosal tumor-like protrusion. In addition, lymph node metastasis was presented within the serous membrane and superior mesenteric lymph nodes. We reported a case of tubular adenocarcinoma, and poorly differentiated adenocarcinoma developing from hyperplastic and serrated adenoma, leading to lymph duct progression and severe lymph node metastasis. This case showed unique development and progression, and we presented characteristic imaging findings.