Inflammatory bowel diseases (IBD) represent a group of chronic systemic inflammatory conditions with predilection to gastrointestinal tract and include Crohns disease and ulcerative colitis. If the IBD cannot be further specified, a term unclassified IBD is used. Histopathological diagnosis of IBD relies on identifying a chronic inflammatory pattern in proper topographic distribution, showing structural abnormalities of the intestinal mucosa and characteristic cellular composition of the inflammatory infiltrate. The intestinal involvement in Crohns disease is typically segmental, with predilection for terminal ileum and presence of epithelioid granulomas in histology. Ulcerative colitis shows a diffuse pattern of the inflammation and usually affects a rectum, with variable extension towards a terminal ileum. However, there is an expanding knowledge about etiopathogenesis, morphology and clinical presentation of IBD, which led to detailed phenotypic subclassification and defined many atypical variants. As a result, diagnosis of IBD became complex multidisciplinary process. The aim of this work is to present an overview of IBD morphology and to provide a base for histopathological diagnosis of IBD on both bioptic samples and surgical resections.

Advances in gut microbiota functions in inflammatory bowel disease: Dysbiosis, management, cytotoxicity assessment, and therapeutic perspectives