Imaging description

Non-occlusive mesenteric ischemia (NOMI) is a condition in which bowel ischemia occurs secondary to slow flow in the mesenteric vessels in the absence of thrombosis. CT angiography demonstrates patent origin of the proximal vessels with poor visualization and pruning of the distal vasculature (Figures 78.1, 78.2, 78.3). Delayed opacification of the mesenteric veins may be seen. Thickening of the bowel wall with or without pneumatosis may also be present (Figure 78.3). Selective angiography of mesenteric arteries serves as the gold standard in diagnosing NOMI.

Importance

A low-flow state can be seen in conditions like hypovolemic shock, sepsis, heart failure, hypovolemia due to dehydration, and after dialysis in patients with chronic renal failure. NOMI constitutes about 25% of all cases of acute mesenteric ischemia with mortality as high as 70%. The blood is shunted to maintain perfusion of the brain and heart, and an underlying cardiovascular disease may help precipitate the event. Although reversible, persistent ischemia may lead to bowel infarction. Superimposed infection may also occur. Accurate diagnosis is important as the treatment options differ from occlusive bowel ischemia and include correction of the underlying predisposing factor along with local or systemic vasodilators.

Typical clinical scenario

The typical scenario is of an older patient with underlying cardiovascular disease presenting with hypotension and decreased cardiac output followed by severe abdominal pain. Bowel sounds may be absent and gastrointestinal bleeding can also occur.

Differential diagnosis

Other causes of bowel ischemia such as arterial occlusion from atherosclerotic or thromboembolic disease and venous thrombosis of the mesenteric vasculature may be considered. In both cases filling defect in the effected vasculature may be seen (Figures 78.4 and 78.5).

Teaching point

NOMI is an important cause of ischemic bowel with high mortality and can be differentiated from other causes of bowel ischemia by the presence of narrowed mesenteric vasculature and absence of filling defects within the vessels.