Non-occlusive mesenteric ischemia

Non-occlusive mesenteric ischemia is the second most common cause of acute mesenteric ischemia, with a higher incidence in hospitalized and critical care patients. 

Epidemiology

Non-occlusive mesenteric ischemia accounts for ~25% (range 20-30%) of acute mesenteric ischemia. It most commonly affects patients >50 years ³. 

Risk factors

• atrial fibrillation ⁵

Pathology

Non-occlusive mesenteric ischemia occurs without arterial or venous occlusion in the region of bowel ischemia/infarction ¹. 

Etiology

Systemic hypoperfusion from numerous causes ^2,3:

• cardiac disease (e.g. myocardial infarction)

• systemic hypotension (e.g. cardiogenic, septic, or hemorrhagic shock) resulting in shock bowel

• blunt abdominal trauma

• hypotension following dialysis 

• cardiac or major abdominal surgery

Medication-induced mesenteric vasospasm (e.g. vasoconstriction from digitalis, amphetamines, cocaine, vasopressin) can also be a cause ².

Radiographic features

CT

CT has lower sensitivity for non-occlusive mesenteric ischemic compared to the occlusive type but maintains a high specificity, thus negative CT findings are insufficient to rule out the diagnosis ⁵.

Findings of bowel ischemia (e.g. portal venous gas, pneumatosis intestinalis, abnormal bowel wall enhancement) may be present and the affected bowel may be in watershed areas. CT angiography can show mesenteric arterial narrowing and reduced superior mesenteric artery caliber ^2-5. 

Features of CT hypoperfusion complex may also be present and evaluation of extra-intestinal viscera is important ².