Definitions and Physiology of Crohn’s Disease Crohn's disease is a chronic inflammatory bowel disease that starts with crypt inflammations and abscesses, which then progress into tiny focal aphthous ulcers. Crohn's disease typically begins between ages 15 and 40. It affects the distal ileum and colon and can occur in any part of the digestional tract. Transmural spread of the inflammation can lead to Lympedma (which is a lymphatic obstruction) and thickening of the bowel wall and mesenteries. Mesenteric fat typically extends onto the serosal surface (outer surface) of the bowel....