The connective tissue changes of Crohn's disease.

Although the inflammatory pathology of Crohn's disease is manifestly its most important attribute, the connective tissue changes are important in the genesis of the more chronic features of the disease, and yet these have received little attention from clinicians, pathologists, and scientists. Fat-wrapping appears to be pathognomonic of Crohn's disease, and is an important marker of disease for surgeons. There is evidence of a complex interplay between the effector inflammatory cells of Crohn's disease and adipocytes, hyperplasia of which results in fat-wrapping. Pathologically, this is exhibited in the close relationship between the transmural inflammation that is so characteristic of Crohn's disease and fat-wrapping. Fibrosis and muscularization are also important components of the chronic changes of intestinal Crohn's disease. Neuronal and vascular changes make up the remaining connective tissue changes: these constitute a distinctive feature, and are even specific for Crohn's disease. For pathologists, the combination of these connective changes will allow a diagnosis of chronic 'burnt-out' Crohn's disease, even in the absence of its highly characteristic inflammatory features. The connective tissue changes of Crohn's disease form an important part of its long-term pathology. They deserve more attention from clinicians, diagnostic pathologists and researchers alike.