Colonic muco-submucosal elongated polyp misdiagnosed as an inverted colonic diverticulum.

Colonic muco-submucosal elongated polyp is a large intestine polyp with a long and broad stalk and a "worm-like" appearance which is covered by normal mucosa. The submucosal layer consists of edematous and fibrotic interstitium, adipose tissue, dilated blood vessels, and lymphatic follicles. Endoscopic magnification of the mucosal surface showed a uniform honeycomb pattern of regular colonic muco-submucosal elongated polyp vessels, with soft and deformable "folds" and "gyrus" at the top. The exact pathogenesis of CMSEP is still unclear.