Mesenteric ischemia is a condition which refers to a low blood-flow state of one or more of the three arteries supplying the digestive tract. The three arteries which can be involved in this condition are:

Of these, the celiac and superior mesenteric are the most commonly involved.

Clinical features
There are two forms of mesenteric ischemia: acute and chronic. Acute mesenteric ischemia generally causes sudden and severe abdominal pain, often associated with vomiting and diarrhea. In some illnesses affecting circulation, including conditions associated with low blood pressure or heart failure, mesenteric ischemia can occur due to the underlying condition.

The chronic form is associated with often nonspecific symptoms. Abdominal pain 30 minutes to 90 minutes after eating is common, and is referred to often as "abdominal angina". The pain generally fades, but returns when the patient eats again. Patients often begin to eat less due to the discomfort, usually resulting in weight loss, often severe or life-threatening. Other chronic symptoms can include nausea, vomiting, diarrhea, and constipation. In some cases, bleeding from the affected portion of the gut can occur. Ileus (decreased activity of the intestines) can also occur due to the low blood flow.

Pathogenesis
Acute mesenteric ischemia, like strokes and heart attacks, is caused when one of the arteries is blocked by an embolism (blood clot), or thromboses. The chronic form is caused by gradual buildup of blockages within the arteries, and is a form of atherosclerosis.

Risk factors for the chronic form of mesenteric ischemia include smoking, high cholesterol, and high blood pressure. It is more common in males and in the elderly. In some cases, rapid weight loss for other reasons can induce mesenteric ischemia if a patient is already prone to the condition. This is thought to be because of downward traction on an already-narrowed artery as fatty tissues in the abdomen decrease and the intestines displace downward.

Diagnosis
Arteriography (or angiography) are the gold standard tests for diagnosing this condition. The traditional way is by catheterization and the use of radio-opaque dyes. Computerized tomography can sometimes be of benefit, and has already been done in some cases while searching for other illnesses. Strides in the field of magnetic resonance imaging have made MRA (magnetic resonance angiography) a viable alternative however.

Treatment
Acute mesenteric ischemia is almost exclusively treated by emergency sugical intevention. surgical treatment is usually required to effectively treat chronic mesenteric ischemia as well. If the blockage is sufficiently proximal and accessible, catheterization and balloon dilation or placement of a stent is sometimes an option.

Natural course
Untreated acute mesenteric ischemia is almost always fatal. With loss of blood flow to portions of the gut, necrosis occurs, and the bowel contents including bacterial flora can escape into the abdominal cavity causing peritonitis. Death from sepsis is almost always the end result. Chronic mesenteric ischemia has a more indolent course and sysmptoms can drag on for months or years before a correct diagnosis is made. Ultimately, if left untreated, severe weight loss and malnutrition usually contribute to the patient's demise.

Prognosis
Acute mesenteric ischemia has mortality rates as high as 85% without immediate treatment. Mortality rates climb significantly if peritonitis occurs due to ischemia. If a significant portion of the intestinal tract becomes necrotic and dies, there is no way to prevent the death of the patient. Untreated chronic mesenteric ischemia has a high rate of morbidity as well, but a lower mortality rate.


References
www.vanderbilt.edu/biomag/mesich.htm
www.hmc.psu.edu/healthinfo/m/mesentericischemia.htm
www.fpnotebook.com/SUR6.htm
www.emedicine.com/emerg/topic311.htm

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