Colitides: diagnostic challenges and a pattern based approach to differential diagnosis

The etiologies of colonic injury and inflammation are many and varied. The most commonly encountered colitides in clinical practice are associated with inflammatory bowel disease, infection, ischemia, radiation, diverticulosis, and medications. Like the rest of the gastrointestinal (GI) tract, the colon has a limited set of responses to various types of injury and therefore there is significant overlap between many of these disorders. Microscopic recognition of the pattern of injury is essential in constructing the differential diagnosis and identifying or at least suggesting the possible cause of injury. The aim of this article is to review the most commonly encountered colitides using a practical pattern based approach, to provide some guidance in differentiating between these patterns and to highlight some of the challenges faced by pathologists in approaching such cases in daily practice.