A case of pedunculated colonic adenoma with pseudocarcinomatous invasion and squamous metaplasia occurring in the sigmoid colon

: A case of pedunculated colonic adenoma with pseudocarcinomatous invasion and squamous metaplasia occurring in the sigmoid colon is reported. The patient was a 65-year-old man who visited our hospital for further evaluation of a positive fecal occult blood test. Colonoscopy revealed a pedunculated polyp with a thick swollen stalk in the sigmoid colon. EUS revealed a hyperechoic lesion in the stalk. However, endosonographically, the third and fourth layers of the colonic wall were shown to be normal. It was suspected to be a colonic adenoma with pseudocarcinomatous invasion from these endoscopic findings. Endoscopic polypectomy was performed. Histological examination of the specimen revealed tubular adenoma with moderate epithelial atypia and submucosal displacement of adenomatous glands with variable cystic changes. Squamous metaplasia and hemosiderin deposition were also seen in the mucosal and submucosal layer, respectively. This polyp was diagnosed as a colonic adenoma with pseudocarcinomatous invasion with squamous metaplasia.