Perforation of viscus

Mesenteric vascular occlusion leading to intestinal infarction and secondary peritonitis

Inflammatory conditions with localized, followed by generalized peritonitis (e.g. appendicitis, cholecystitis, diverticulitis, Crohn's disease abscess, pancreatitis)

Late intestinal obstruction (most commonly due to large bowel tumour, adhesions, hernia or volvulus)

Perforated duodenal ulcers are now relatively uncommon. Perforated colonic (or less commonly, small bowel) diverticula may be encountered. Most cases of perforation of the upper and lower GI tract are related to endoscopic procedures (e.g. polypectomy).

Elderly patients and those on long-term corticosteroids may not manifest typical symptoms of peritonitis and signs may be misleadingly mild.

Thrombosis complicating atherosclerotic disease of the mesenteric arteries, polycythaemia, sickle cell disease, cryoglobulinaemia and amyloidosis

Embolism from the heart (e.g. atrial fibrillation, endocarditis)

Aortic dissection (Chapter 50)

Vasculitis

Always consider a cardiac source of emboli in patients with atherosclerosis who present with features suggestive of acute mesenteric ischaemia.

Polyarteritis nodosa is often overlooked as a cause of vasculitic mesenteric infarction as the autoantibody screen is typically negative.

Common causes are gallstones (50% cases) and alcohol (20%)

Less common causes include endoscopic retrograde cholangiopancreatography (ERCP) and severe hyperlipidaemias

Atherosclerotic and inflammatory factors contribute to the pathogenesis of abdominal aortic aneurysm

Risk of rupture greatly increased in male smokers >65 y and in aneurysms >5.5 cm in diameter

Typically causes acute severe abdominal, flank or back pain. Syncope without prominent pain can be a presentation.

May also result in leg or spinal cord ischaemia.