Acute: 5 per 100,000 per year (developed world) Chronic: 1 per 100,000
Mesenteric ischemia is a medical condition in which injury to the small intestine occurs due to not enough blood supply. It can come on suddenly, known as acute mesenteric ischemia, or gradually, known as chronic mesenteric ischemia. The acute form of the disease often presents with sudden severe abdominal pain and is associated with a high risk of death. The chronic form typically presents more gradually with abdominal pain after eating, unintentional weight loss, vomiting, and fear of eating.
Acute mesenteric ischemia affects about five per hundred thousand people per year in the developed world. Chronic mesenteric ischemia affects about one per hundred thousand people. Most people affected are over 60 years old. Rates are about equal in males and females of the same age. Mesenteric ischemia was first described in 1895.
While not always present and often overlapping, three progressive phases of mesenteric ischemia have been described:
A hyper active stage occurs first, in which the primary symptoms are severe abdominal pain and the passage of bloody stools. Many patients get better and do not progress beyond this phase.
A paralytic phase can follow if ischemia continues; in this phase, the abdominal pain becomes more widespread, the belly becomes more tender to the touch, and bowel motility decreases, resulting in abdominal bloating, no further bloody stools, and absent bowel sounds on exam.
Symptoms of mesenteric ischemia vary and can be acute (especially if embolic), subacute, or chronic.
Case series report prevalence of clinical findings and provide the best available, yet biased, estimate of the sensitivity of clinical findings. In a series of 58 patients with mesenteric ischemia due to mixed causes:
In the absence of adequate quantitative studies to guide diagnosis, various heuristics help guide diagnosis:
Mesenteric ischemia "should be suspected when individuals, especially those at high risk for acute mesenteric ischemia, develop severe and persisting abdominal pain that is disproportionate to their abdominal findings"., or simply, pain out of proportion to exam.
Regarding mesenteric arterial thrombosis or embolism: "early symptoms are present and are relative mild in 50% of cases for three to four days before medical attention is sought".
Regarding mesenteric arterial thrombosis or embolism: "Any patient with an arrhythmia such as atrial fibrillation who complains of abdominal pain is highly suspected of having embolization to the superior mesenteric artery until proved otherwise."
Regarding nonocclusive intestinal ischemia: "Any patient who takes digitalis and diuretics and who complains of abdominal pain must be considered to have nonocclusive ischemia until proved otherwise."
It is difficult to diagnose mesenteric ischemia early. One must also differentiate ischemic colitis, which often resolves on its own, from the more immediately life-threatening condition of acute mesenteric ischemia of the small bowel.
In a series of 58 patients with mesenteric ischemia due to mixed causes:
Lactic acid elevated 91% (probably an overestimate as only tested in 57% of patients)
In very early or very extensive acute mesenteric ischemia, elevated lactate and white blood cell count may not yet be present. In extensive mesenteric ischemia, bowel may be ischemic but separated from the blood flow such that the byproducts of ischemia are not yet circulating.
A number of devices have been used to assess the sufficiency of oxygen delivery to the colon. The earliest devices were based on tonometry, and required time to equilibrate and estimate the pHi, roughly an estimate of local CO2 levels. The first device approved by the U.S. FDA (in 2004) used visible light spectroscopy to analyze capillary oxygen levels. Use during aortic aneurysm repair detected when colon oxygen levels fell below sustainable levels, allowing real-time repair. In several studies, specificity has been 83% for chronic mesenteric ischemia and 90% or higher for acute colonic ischemia, with a sensitivity of 71%-92%. This device must be placed using endoscopy, however.
Plain X-rays are often normal or show non-specific findings.
Evidence of adjacent solid organ infarctions to the kidney or spleen, consistent with a cardiac embolic shower phenomenon
In embolic acute mesenteric ischemia, CT-Angiography can be of great value for diagnosis and treatment. It may reveal the emboli itself lodged in the superior mesenteric artery, as well as the presence or absence of distal mesenteric branches. 
Late findings, which indicate dead bowel, include:
As the cause of the ischemia can be due to embolic or thrombotic occlusion of the mesenteric vessels or nonocclusive ischemia, the best way to differentiate between the etiologies is through the use of mesenteric angiography. Though it has serious risks, angiography provides the possibility of direct infusion of vasodilators in the setting of nonocclusive ischemia.
The treatment of mesenteric ischemia depends on the cause, and can be medical or surgical. However, if bowel has become necrotic, the only treatment is surgical removal of the dead segments of bowel.
In non-occlusive mesenteric ischemia, where there is no blockage of the arteries supplying the bowel, the treatment is medical rather than surgical. People are admitted to the hospital for resuscitation with intravenous fluids, careful monitoring of laboratory tests, and optimization of their cardiovascular function. NG tube decompression and heparin anticoagulation may also be used to limit stress on the bowel and optimize perfusion, respectively.
Surgical revascularisation remains the treatment of choice for mesenteric ischaemia related to an occlusion of the vessels supplying the bowel, but thrombolytic medical treatment and vascular interventional radiological techniques have a growing role.
If the ischemia has progressed to the point that the affected intestinal segments are gangrenous, a bowel resection of those segments is called for. Often, obviously dead segments are removed at the first operation, and a second-look operation is planned to assess segments that are borderline that may be savable after revascularization.
Methods for revascularization
Open surgical thrombectomy
Trans-femoral antegrade mesenteric angioplasty and stenting
^Font VE, Hermann RE, Longworth DL (1989). "Chronic mesenteric venous thrombosis: difficult diagnosis and therapy". Cleveland Clinic Journal of Medicine. 56 (8): 823–8. doi:10.3949/ccjm.56.8.823. PMID2691119.
^Evennett NJ, Petrov MS, Mittal A, Windsor JA (July 2009). "Systematic review and pooled estimates for the diagnostic accuracy of serological markers for intestinal ischemia". World J Surg. 33 (7): 1374–83. doi:10.1007/s00268-009-0074-7. PMID19424744.
^Smerud M, Johnson C, Stephens D (1990). "Diagnosis of bowel infarction: a comparison of plain films and CT scans in 23 cases". AJR Am J Roentgenol. 154 (1): 99–103. doi:10.2214/ajr.154.1.2104734. PMID2104734.
^Schoots IG, Koffeman GI, Legemate DA, Levi M, van Gulik TM (2004). "Systematic review of survival after acute mesenteric ischaemia according to disease aetiology". The British Journal of Surgery. 91 (1): 17–27. doi:10.1002/bjs.4459. PMID14716789.