Diversion colitis--new light through old windows.

Diversion proctocolitis is an iatrogenic disorder caused by surgical diversion of the faecal stream away from the colorectal mucosa. Such surgery may be necessary in cases of tumour, trauma or inflammatory conditions of the colorectum. Histopathological change is characterized by a chronic lymphoplasmacytic inflammatory infiltrate, and the hallmark feature, lymphoid follicular hyperplasia. Histological appearances are determined by the disease state of the colonic mucosa prior to faecal diversion. Macroscopic appearances may vary considerably, but often include aphthoid ulceration. The exact pathogenesis of the condition remains unclear, but the removal of short-chain fatty acids, present in the faecal stream, is considered an important aetiological factor. Current research areas, including the microbiology and cellular kinetics of diversion colitis, are discussed along with clinical features and treatments.