GRANULOMATOUS colitis may involve any portion of the large bowel. Although an extensive length of intestine is diseased in many cases, segmental lesions are not uncommon. When segmental disease occurs in patients of middle or old age, it may involve a portion of the colon, usually the sigmoid, where multiple diverticula are also present. Difficulty then arises in differentiating granulomatous colitis from diverticulitis. An unusual feature of both diseases is the presence of a paracolic fistulous tract.
Paracolic longitudinal tracts of the sigmoid were originally thought to be secondary only to diverticulitis. In 1970 we1 reported that paracolic longitudinal tracts also occur in granulomatous colitis, usually in association with diverticula. It was suggested that the transverse fissures of Crohn's disease penetrate the mucosal herniations of the diverticula to produce fistulous tracts. We also postulated that when the tract exceeded 10 cm in length, its presence was pathognomonic for granulomatous colitis.
Richard H. Marshak, Arthur E. Lindner, Daniel Maklansky. Paracolic Fistulous Tracts in Diverticulitis and Granulomatous Colitis. JAMA. 1980;243(19):1943–1946. doi:10.1001/jama.1980.03300450047026