A 68-year-old man was referred to our hospital because of watery diarrhea lasting for three months. On colonoscopy, severe luminal stenosis with coarse granular mucosa was observed in the rectosigmoid colon. Based on the findings of imaging and histological examinations, ischemic colitis due to either inferior mesenteric venous occlusion or disordered venous perfusion associated with thrombosis or arteriovenous malformation was suspected. However, Hartmanns operation was performed considering the possibility of type 4 colorectal cancer. Histological examination of the resected specimen revealed a small superficial depressed rectal adenocarcinoma accompanied by marked venous invasion with a tumor embolus in the inferior mesenteric vein, that caused long-segmental ischemic change of the rectosigmoid colon. We herein report this unusual case of superficial rectal cancer that required differentiation from ischemic colitis caused by other morbidities.
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