Case 1 -

Diversion Colitis Laura W. Lamps, M.D. Audrey J. Lazenby, M.D. Joel K. Greenson, M.D.

Clinical Presentation: These rectal biopsies are from a 38 year old man with Crohn's disease, status post resection of his terminal ileum and right colon. He has an ileostomy and a Hartmann's pouch. Case 1 - Figure 1 - Low magnification view showing superficial mucosal erosion and prominent mucosal lymphoid aggregates, yet no significant architectural distortion. Case 1 - Figure 2 - Higher magnification of the prominent lymphoid aggregates typical of diversion colitis. Although some cases of diversion colitis have cryptitis and crypt abscesses, this case does not. Endoscopic Findings: The endoscopist described streaky erythema without ulcers in the Hartmann's pouch Diagnosis : Diversion colitis General Comments: Diversion colitis is an inflammatory process that occurs in segments of the large bowel that are excluded from the fecal stream, as in patients with an ileostomy or colostomy. It is found in 50-100% of patients following colonic bypass, and is cured by surgical reversal of this condition. While this is often an incidental finding in asymptomatic patients, some may present with mucoid or bloody discharge and/or abdominal pain. The condition occurs 3 –36 months following colonic exclusion and completely regresses within 3 months of re-establishment of the fecal stream. Symptoms occur more frequently with increased duration of diversion. Pathologic features: The gross and endoscopic features of diversion colitis include erythema, friability, edema, and nodularity with apthous ulcers. Histologically, the nodularity corresponds to large lymphoid aggregates with prominent germinal centers. The histologic features of diversion colitis are quite variable. Typically, one sees lamina propria plasmacytosis with prominent lymphoid follicles, often accompanied by cryptitis, crypt abscesses, and neutrophils within the lamina propria. Crypt architecture generally remains intact. In some instances, however, the inflammation may mimic severe ulcerative colitis, complete with crypt distortion and marked chronic inflammation of the lamina propria. In other cases, patchy cryptitis and aphthous lesions may mimic Crohn's disease. Pathogenesis: The cause of diversion colitis is thought to be a deficiency of short-chain fatty acids, which are usually derived from fermentation of dietary starches by normal colonic bacterial flora. Short-chain fatty acids are the main source of energy for colonocytes. Once the fecal stream is diverted, dietary starches are no longer present. Somehow this lack of colonocyte nutrition leads to an inflammatory disorder. If re-anastomosis and restoration of the fecal stream is not possible, the inflammation can be reversed by giving short-chain fatty acids via enemas several times a week. Differential diagnosis: Because the histology is so variable, the key to making this diagnosis rests in knowing that the biopsies come from a diverted segment of colon. Pathologists should remember that a Hartmann's pouch is a diverted segment of colon that virtually always shows some element of diversion colitis (not pouchitis). Even in patients with Crohn's disease, the presence of a focally active colitis with aphthous ulcers should be considered to be diversion colitis, as previous studies have shown that these changes will quickly regress once the fecal stream is re-established. Biopsies of a diverted segment are often taken prior to re-establishing the fecal stream, at which time it is critical that the pathologist make the correct diagnosis. If the pathologist is not told that the biopsies in question are from a diverted segment of colon, he or she will probably diagnose some form of chronic inflammatory bowel disease. This errant diagnosis will likely delay the patients' surgery and lead to unnecessary anti-inflammatory therapy. References: Glotzer DJ, Glick ME, Goldman H. Proctitis and colitis following diversion of the fecal stream. Gastroenterology 80:438-41;1981. Komorowski RA. Histologic Spectrum of Diversion Colitis. Am J Surg Pathol 14:548-54;1990. Harig JM, Soergel KH, Komorowski RA, Wood CM. Treatment of diversion colitis with short-chain fatty acid irrigation. N Engl J Med 320:23-28;1989. Haque S, Eisen RN, West AB. The morphologic features of diversion colitis: Studies of a pediatric population with no other disease of the intestinal mucosa. Hum Pathol 24:211-19;1993. Korelitz BI, Cheskin LJ, Sohn N, Sommers SC. Proctitis after fecal diversion in Crohn's disease and its elimination with reanastomosis: Implications for surgical management. Gastroenterology 87:710-13;1984. Ma CK, Gottlieb C, Haas PA. Diversion colitis: a clinicopathologic study of 21 cases. Hum Pathol 1990;21:429-36.