Pathology of the defunctioned rectum in ulcerative colitis.

Faecal stream diversion may induce inflammatory changes in the defunctioned segment of the large intestine. These changes are predominantly mucosal, although confusing histological features including granulomas may be present. The pathology of 15 defunctioned rectal stumps has been studied. All patients had previously undergone urgent total colectomy for ulcerative colitis and rectal stumps had been left in situ while they awaited pelvic ileal reservoir construction. All rectal stumps showed predominantly mucosal disease but there were additional features such as florid lymphoid follicular hyperplasia (12 cases), transmural inflammation (nine cases), granulomas (four cases), fissures (eight cases), and changes akin to ischaemia or to pseudomembraneous colitis (four cases). These changes may result from a combination of defunctioning and of active ulcerative proctitis. Some induce a histological appearance that may mimic Crohn's disease. Nevertheless review of all 15 colectomy specimens showed unequivocal ulcerative colitis and none of the patients has subsequently shown any clinical, radiological, or pathological evidence to support a diagnosis of Crohn's disease. Histology of the rectal stump in ulcerative colitis may lead to an erroneous diagnosis of Crohn's disease and the patient may subsequently be denied the advantage of a pelvic ileal reservoir.