Mural bridging lesions in colonic Crohn's disease.

A case of Crohn's colitis with mural bridging lesions is described. The bridging lesions comprised colonic-type mucosa, smooth muscle, nerve fibers, with foci of adipose tissue and fibrous connective tissue. The lesions arose from the muscularis propria proximal to colonic strictures and possibly due to diverticular outpouching of the colonic wall associated with increased intraluminal pressure, although the exact mechanism of their formation appears unclear. This entity has not been previously described in inflammatory bowel disease, to our knowledge. Bridging pseudopolyps are seen in ulcerative colitis and rarely in Crohn's disease but do not contain substantial amounts of smooth muscle and/or nerve fibers. We believe that the mural bridges described in this article represent residual muscularis propria at the site of diverticular formation due to long-standing Crohn's colitis. We speculate that the stricture formation seen distal to the site of the mural bridging lesions may have been an important factor in formation of the colonic diverticula and, hence, these lesions that we interpret as representing residual muscularis propria adjacent to sites of diverticular formation in long-standing Crohn's colitis.