The superior mesenteric artery occlusion
The superior mesenteric artery occlusion is the gastrointestinal artery most commonly involved in acute, occlusive events leading to ischaemia. It supplies the small bowel apart from the proximal duodenum and drains via the superior mesenteric vein into the portal system

>>> signs and symtoms

The patient with an acute occlusion to their superior mesenteric artery may present with a sudden onset, severe colicky abdominal pain. The patient is classically elderly and has a past history of cardiac or arterial disease. Occasionally, the pain is vague and insidious.

Vomiting and diarrhoea can develop, and both may have a bloody element due to slow haemorrhage into the bowel lumen.

Physical signs are minimal initially and the patient is classically noted at this time to have pain out of proportion to the examination findings. However, as necrosis passes outwards from the mucosa, guarding, tenderness, abdominal distention and an absence of bowel sounds are apparent. Shock is a late sign.

>>>aetiology

thromboembolic arterial occlusion
mesenteric venous occlusion
systemic vasculitis
cardiovascular causes
secondary to intestinal obstruction
strangulated hernia
intussusception - usually in children
volvulus - usually small bowel or sigmoid colon
>>>diagnosis

The diagnosis of occlusion of the superior mesenteric artery is often too late to save the patient's life. This is because the clinical presentation is often deceptive: signs are deceptively sparse and investigation is usually inconclusive at an early stage.

This condition should always be suspected in an arteriopath who develops unexplained abdominal pain. Prompt laparotomy to search for 'pale and pulseless' bowel is the best policy.

>>>Investigations

Patients with occlusion of the superior mesenteric artery may be investigated along the following lines:

FBC: may show leucocytosis
biochemistry:
mildly raised serum amylase
increased inorganic phosphate indicates intestinal infarction
metabolic acidosis
radiology:
plain abdominal X-ray:
absence of bowel gas at first
later, appearances of ileus, mucosal oedema and gas in the bowel wall and portal vein
mesenteric angiography: often diagnostic, but difficult to do in the moribund patient
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