Diversion colitis: histological features in the colon and rectum after defunctioning colostomy.

Diversion of the faecal stream by ileostomy or colostomy leads to inflammation in the defunctioned segment, known as diversion colitis. The affected bowel is rapidly restored to normality by reanastomosis. Diversion colitis should not be mistaken for inflammatory bowel disease, for which reanastomosis would be inappropriate. Studies of biopsy material from patients with diversion colitis have shown a variety of histological features, but no consistent pattern. The histology in resection specimens of defunctioned large bowel from 15 patients with no pre-existing inflammatory bowel disease was studied. Nine patients had symptoms of abdominal pain or rectal discharge of blood or mucus that developed between 9 months and 17 years after diversion procedure. The histology was abnormal in all. Findings were similar in 14 patients, regardless of the duration of faecal diversion, and comprised diffuse mild chronic inflammation with or without mild crypt architectural abnormalities, crypt abscesses, or follicular lymphoid hyperplasia. One patient had more severe changes, resembling active ulcerative colitis. These features in biopsy specimens are unlikely to be diagnostic but should provide useful information in avoiding a mistaken diagnosis of inflammatory bowel disease in these patients.