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Acute superior mesenteric artery occlusion

An acute superior mesenteric artery occlusion, which can then result in an acute mesenteric ischaemia, can be a life threatening event related to the artery supplying the majority of the small bowel and right side of the colon

Epidemiology 

An acute occlusion is an uncommon event that typically affect elderly patients, who are at increased risk of other cardiovascular events. 

Clinical presentation

Clinical presentation is variable and unfortunately often non-specific such that the diagnosis is not made for some time. It may be dramatic with acute onset severe abdominal pain, or less well defined 4.

Pathology

Acute occlusion can be due to a number of causes 3,4 :

  • embolic event: ~ 60%
  • acute in situ thrombosis superimposed on atherosclerosis: 30%
  • aortic dissection with involvement of the SMA origin
  • slow flow or idiopathic 

Risk factors therefore include:

  • advanced age
  • smoking
  • prothrombotic tendency
    • antiphospholipid antibodies, etc. 2
  • valvular/cardiac abnormalities
    • mechanical heart valve
    • atrial fibrillation
    • AMI
    • ventricular aneurysm
  • right to left shunt
    • PFO/ASD with paradoxical embolism

Radiographic features

CT

Computed tomography is widely accepted as the first line imaging technique in this evaluation7 due to its speed, widespread availability and ability to diagnose other causes of acute abdominal pain.

Technique

For a discussion on CT technique refer to intestinal ischaemia article. 

Findings

Findings in acute superior mesenteric artery occlusion include:

  • lack of enhancement of the lumen of the SMA and/or its branches
    • embolism lodgement location varies
  • bowel wall
    • thickness
      • variable
      • in pure arterial occlusion wall may be thinned (aka paper-thin wall) due to  loss of intestinal muscular tone and absence of blood  6
      • thickened wall may also be present but does not correlate with severity 6
    • enhancement absent
    • once necrotic mural gas may be present (pneumatosis intestinalis
  • ileus
  • free fluid
  • portal venous or intrahepatic gas
  • free intra abdominal gas
Ultrasound

Ultrasound is able to demonstrate normal flow in both SMA and SMV, but is incapable of assessing side branches or the bowel wall. It has little role in the acute management of this condition.

Angiography

Although once the gold standard for diagnosis, increasingly it is reserved for those patients deemed to perhaps benefit from endovascular intervention.

Treatment and prognosis

An acute SMA occlusion has a mortality of over 60-80% despite treatment 3,5. Treatment options include 4:

  • endovascular thrombectomy
  • intraluminal papaverine
  • surgical thrombectomy +/- resection of infarcted bowel

Differential diagnosis

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