Diverticular disease-associated segmental colitis.

Diverticular disease-associated segmental colitis is a unique variant of chronic colitis limited to segments of the left colon that harbor diverticula. Histologically, this disease mimics chronic idiopathic inflammatory bowel disease and can be indistinguishable from ulcerative colitis or Crohn's colitis on histologic grounds alone. Patients typically present with hematochezia and cramping abdominal pain, and colonoscopic evaluation reveals inflammatory changes limited to the segment of bowel containing the diverticula, with rectal sparing. Although this disease does not appear to be an unusual form of diverticulitis but possibly an immunologically mediated process, many patients respond to treatment directed toward diverticulitis. A subset of patients requires immunosuppressive therapy and/or surgery, and a small subset progresses to develop classic ulcerative colitis. Because of the histologic overlap with ulcerative colitis and occasionally Crohn's colitis, it is essential that endoscopists provide a full description of the macroscopic appearance of the inflammatory changes at endoscopy, such as limitation to a segment of diverticular disease, so that the pathologist can provide a more informative interpretation of the biopsy.