Contribution of morphology for the comprehension of mechanisms of fibrosis in inflammatory enterocolitis.

Strictures are a common complication of Crohn's disease and an indication for surgery in approximately 50% of patients. Morphologic studies have shown that fibrosis of the submucosa and muscularis propria are common in Crohn's disease, especially in strictures. Immunohistochemical and in situ hybridization studies have demonstrated a marked increase of various subtypes of collagens in Crohn's disease. Collagens type I and III are present in ulcerated areas where they appear around capillaries and in a linear deposition at the junction between the granulation tissue and the necrotic debris. Collagens type IV and V show a prominent perivascular expression, increased deposition in the muscularis propria and increased expression around ganglia. Initiation and maintenance of the connective tissue changes are related with the inflammatory infiltrate. Inflammatory cells can further alter smooth muscle proliferation and migration and promote the formation of myofibroblasts. These alterations together with increased collagen deposition are involved in the complex process of strictures and bowel wall alterations in Crohn's disease.