From aphthous ulcer to full-blown Crohn's disease.

At onset, Crohn's disease (CD) is characterized by transmural inflammation with mucosal ulcerations. In its earliest phase the lesions are mainly aphthous ulcers. The ulcers then become larger, a nodular pattern develops and penetration of the deep ulcers leads to fistulas and collagen deposition to fibrotic strictures. The best model to study the earliest lesions in CD is the postoperative recurrence situation where these early lesions recur within weeks to months after surgery. CD recurrence is triggered by the fecal contents of the gut since temporary diversion prevents the recurrence of bowel inflammation. With the development of newer techniques, such as microarray analysis of total mucosal gene expression and molecular analysis of gut content and mucosal microbiome, this model will allow to shed light on the earliest pathogenic features of CD.