Long pedunculated colonic polyp composed of mucosa and submucosa: proposal of a new entity, colonic muco-submucosal elongated polyp.

We encountered 15 patients with colonic polyps showing histologic features that did not belong to any of the known categories. All polyps were elongated and drumstick-shaped, with lengths of 12 to 160 (mean, 29 mm) mm. Histologically, the polyps were covered with normal mucosa and consisted of edematous, loose, fibrous, connective tissues and dense, fibrous submucosal layers, often showing dilation of blood vessels and lymphatics. Although the mechanism of generation of such polyps remains unknown, their elongation may be caused by intestinal motion. Because this kind of polyp has not been described previously outside Japan, we here introduce a new type of polyp, which we have proposed calling the colonic muco-submucosal elongated polyp.