Colonic mucosubmucosal elongated polyp: a clinicopathologic study of 13 cases and review of the literature.

Colonic mucosubmucosal elongated polyp (CMSEP) is a distinctive non-neoplastic colorectal polyp characterized by pedunculated, elongated shape and is composed mainly of expanded submucosa with a normal mucosal lining. Only a small number of these polyps have been reported, exclusively from Japan. We report the clinicopathologic characteristics of 13 CMSEPs occurring in 11 patients, mostly from European ancestry. Ten of these polyps were resected during colonoscopy, and 3 were diagnosed in a patient who underwent sigmoid resection for diverticular disease. Among patients who had undergone a colonoscopy, 4 had altered bowel habit, and 1 suffered from abdominal discomfort; the other 5 patients had routine screening colonoscopy. Eight polyps were located in the sigmoid colon, 3 in the right colon, 1 in the rectosigmoid junction, and 1 in the descending colon. Polyp size ranged from 10 to 150 mm. Histologically, CMSEPs were characterized by unremarkable large bowel mucosa and submucosal stalk containing dilated thick-walled veins running parallel to the long axis of the polyp. Mucosal inflammation or fibromuscular proliferation characteristic of mucosal prolapse was absent. The pathogenesis of CMSEP may involve mechanical traction of the mucosa and the superficial submucosa during peristalsis in a fragile area of the colon. Despite the occasional large size, CMSEP is a benign lesion seldom leading to clinical complications.