 Introduction/Background Mesenteric ischemia is an uncommon disease affecting the small and large bowel resulting from a reduction of intestinal blood flow. Although the disease is responsible for fewer than 1 in 1,000 hospital admissions, the mortality rate remains high, ranging between 30% to 90% in acute settings despite advances in treatment options [1-4]. The etiology of ischemia may vary from arterial occlusion, venous thrombosis, or vasoconstriction. Higher prevalence in the elderly population and nonspecific clinical presentation leading to delayed diagnosis contribute to the high mortality rate [1]. Most cases of mesenteric ischemia are due to an acute event leading to decreased blood supply to the splanchnic vasculature. Chronic mesenteric ischemia is uncommon, accounting for <5% of cases of mesenteric ischemia, and is almost always associated with diffuse atherosclerotic disease [5]. Acute embolization of the SMA involves the distal aspect of the vessel, usually beyond the origin of the middle colic artery, and commonly does not have associated collateral vessels. Acute mesenteric artery thrombosis is typically associated with chronic atherosclerotic disease and, given its more insidious course, a well-developed collateral circulation is commonly present. Nonocclusive mesenteric ischemia is seen in the setting of hypoperfusion because of secondary vasoconstriction of the mesenteric arteries. In these cases, there is no evidence of vascular occlusion, and the ischemia is distributed over a wider area of the bowel in a nonconsecutive manner [9]. Mesenteric and portal venous thrombosis is the least common cause of acute mesenteric ischemia and may be idiopathic. Most common risk factors are hypercoagulable states, portal hypertension, and recent surgery [10,11]. Bowel ischemia results from impaired intestinal mucosa venous outflow, leading to visceral edema and subsequent arterial hypoperfusion.
Imaging of Mesenteric Ischemia.  Introduction/Background Mesenteric ischemia is an uncommon disease affecting the small and large bowel resulting from a reduction of intestinal blood flow. Although the disease is responsible for fewer than 1 in 1,000 hospital admissions, the mortality rate remains high, ranging between 30% to 90% in acute settings despite advances in treatment options [1-4]. The etiology of ischemia may vary from arterial occlusion, venous thrombosis, or vasoconstriction. Higher prevalence in the elderly population and nonspecific clinical presentation leading to delayed diagnosis contribute to the high mortality rate [1]. Most cases of mesenteric ischemia are due to an acute event leading to decreased blood supply to the splanchnic vasculature. Chronic mesenteric ischemia is uncommon, accounting for <5% of cases of mesenteric ischemia, and is almost always associated with diffuse atherosclerotic disease [5]. Acute embolization of the SMA involves the distal aspect of the vessel, usually beyond the origin of the middle colic artery, and commonly does not have associated collateral vessels. Acute mesenteric artery thrombosis is typically associated with chronic atherosclerotic disease and, given its more insidious course, a well-developed collateral circulation is commonly present. Nonocclusive mesenteric ischemia is seen in the setting of hypoperfusion because of secondary vasoconstriction of the mesenteric arteries. In these cases, there is no evidence of vascular occlusion, and the ischemia is distributed over a wider area of the bowel in a nonconsecutive manner [9]. Mesenteric and portal venous thrombosis is the least common cause of acute mesenteric ischemia and may be idiopathic. Most common risk factors are hypercoagulable states, portal hypertension, and recent surgery [10,11]. Bowel ischemia results from impaired intestinal mucosa venous outflow, leading to visceral edema and subsequent arterial hypoperfusion.