Ulcerative Colitis - Usually begins in the rectum and May remain localised or extend, sometimes throughout the entire colon. Inflammation affects the mucosa and sub mucosa, in severe cases the muscularis is is involved. The mucus membrane is erythematous, finely granular, friable with scattered haemorrhagic areas. Large mucosal ulcers with copious purulent exudate characterise severe disease. Fistula and abscesses do not occur.
Crohn’s - usually affects distal ileum and colon, but may occur in any part of the GI tract from mouth - anus. Abscesses, internal and external fistula and bowel obstruction may arise. Mucosal lesions develop into oedema creating a cobblestone appearance. Spread of this leads to lymphedema, thickening of the bowel wall and mesentery. Fissures inbetween oedematous islands can extend through the bowel wall to form a fistula. Extensive inflammation may lead to hypertrophy of the mucosa, fibrosis and stricture formation leading to obstruction.