I. Overview
The term viscera generally refers to hollow organs of the gastrointestinal system such as the stomach, small and large intestine and solid organs such as the liver, spleen and pancreas. Visceral ischemic syndromes refer to diseases where there are problems with the blood supply of these organs. The terms mesenteric and visceral ischemia are often used interchangeably. As the organs of the gastrointestinal tract require an adequate blood supply to carry out the digestion of food in order to provide energy for the body, abnormalities of this blood supply may lead to serious nutritional and metabolic problems, which if not corrected, may lead to death.

II. Chronic mesenteric ischemia
In chronic mesenteric ischemia, the disease process generally involves severe disease of all of the main arteries supplying the gastrointestinal tract. The disease, which occurs in these arteries, is usually a result of atherosclerosis or blockage of the blood vessel with hard plaque. The poor blood supply does not allow the gastrointestinal tract to digest food or absorb the digested food into the body. The complaints a patient might have with this disease usually occur over a period of time and occur most commonly after meals (post-prandially). The most common complaint is abdominal pain. This pain may vary from a continuous dull ache to an intermittent or crampy type pain. Patients may associate the eating of food with the development of pain one half to one hour after a meal leading to a fear of eating. This may lead to chronic weight loss and nutritional depletion. Occasionally patients with chronic mesenteric ischemia may develop an episode of sudden severe abdominal pain with nausea, vomiting or diarrhea representing an acute worsening of the blood supply. In this situation the patient should seek medical attention immediately (see acute thrombotic mesenteric ischemia below).

The diagnosis of chronic mesenteric ischemia in patients with the typical complaints mentioned above is usually made with an angiogram or x-ray of the arteries supplying the gastrointestinal tract.  If the angiogram shows severe blockage of these arteries, the blockage may be repaired in several ways. If the blockage is not complete, the radiologist performing the angiogram may be able to dilate or open up the narrowed artery with a special balloon catheter. This procedure is known as balloon angioplasty. Occasionally, a metal support or stent may be placed to prevent the artery from re-narrowing. When it is not possible to do angioplasty or stent placement, surgery to improve the blood supply may be necessary. The type of surgery needed will depend upon where and how extensive the blockage is in the arteries. The surgery may involve either endarterectomy, an incision in the artery with removal of the plaque inside the artery, or bypass. The bypass is usually between the aorta and one or more of the major arteries supplying the gastrointestinal tract.

III. Acute mesenteric ischemia
Acute mesenteric ischemia refers to a sudden, severe reduction in blood flow to the gastrointestinal tract which if not corrected leads to death or infarction of either part of or the entire gastrointestinal tract. This may take one of two forms: occlusive or nonocclusive mesenteric ischemia depending on the presence or absence of blockage within the blood vessels. Furthermore, occlusive acute mesenteric ischemia may involve the arterial or venous blood supply of the gastrointestinal tract.

In acute occlusive arterial ischemia, there is a sudden worsening in the artery(s) may take one of two general forms: embolic or thrombotic. In acute embolic mesenteric ischemia, an embolus or blood clot usually coming from the heart causes the blockage in the artery. This embolus lodges in one of the major arteries of the gastrointestinal tract. The lack of blood flow beyond this may lead to death (infarction) of the intestines. Patients usually complain of severe, unrelenting abdominal pain. The pain may also be accompanied by nausea and/or vomiting. Most patients with this problem have a history of heart problems such as an irregular heartbeat or a heart attack in the past. The pain is severe enough that most patients seek medical help quickly. If the doctor suspects this problem, one of two courses of action will be taken. Either the patient will have an x-ray of the arteries (angiogram) or be taken directly to surgery. The angiogram may show the location of the blockage in the artery supplying the intestines. The vascular radiologist, in this situation, may be able to use thrombolytic therapy, chemical agents which break up the clot within the artery, in an attempt to restore the arterial circulation. Even if this is successful, the patient will need exploratory surgery to determine the presence of any damaged intestine that requires removal. If the surgeon believes there is a high likelihood of damaged (necrotic) intestine, the patient will be taken directly to surgery without angiogram. At surgery, if an embolus is present in the main artery supplying the intestines, it will be removed with a special balloon tipped device. After this is done, any necrotic intestine is removed. These patients will usually undergo exploratory surgery (second look laparotomy) within 48 hours on a planned basis to make sure that the remaining organs of the gastrointestinal tract are healthy.

In acute thrombotic mesenteric ischemia, patients with a severe narrowing in one or more of the major arteries develop a complete blockage in the artery leading to a drastic reduction in blood flow to the gastrointestinal tract. About half of these patients already have complaints of abdominal pain and weight loss consistent with chronic mesenteric ischemia. This is the major reason why patients with chronic abdominal pain after eating should seek medical attention. The patient’s complaints are similar to those of acute embolic mesenteric ischemia. If an angiogram is performed, a severe narrowing (stenosis) in one or more of the major arteries may be opened with a special balloon tipped catheter (balloon angioplasty). A special metal support or strut (stent) may also be placed within the artery for this purpose to prevent re-narrowing. In addition, thrombolytic therapy may be used to dissolve clot lying within the artery. Whether these actions are successful or not in restoring blood flow, the patient will need an operation to determine the presence of any necrotic intestine. At the time of surgery if the major artery(s) remain blocked, a bypass from either the aorta or one of the iliac arteries to one or more of the major arteries of the gastrointestinal tract is performed. These patients will usually undergo a planned second look laparotomy as mentioned above.

In acute mesenteric venous thrombosis, there is a blockage not in the arteries but in the veins, which drain or return blood from the gastrointestinal tract to the heart. The blockage in the veins is caused by a blood clot. Patients with this disease may have a wide spectrum of problems that range from no complaints or a severe catastrophic illness. The most common complaint is abdominal pain This tends to develop more slowly than the pain of mesenteric ischemia due to an arterial blockage. Patients commonly have small or trace amounts of bleeding from the gastrointestinal tract which can be detected by testing the patient’s stool for blood. The diagnosis of mesenteric venous thrombosis can be made with an x-ray of the mesenteric veins or venogram, CAT scan with contrast or a special ultrasound of the mesenteric veins (duplex scan). Patients are given intravenous antibiotics and placed on blood thinning medication or anticoagulation, which is usually continued for the rest of the patient’s life. The radiologist may also use thrombolytic therapy to try and break up the clot in the mesenteric veins. Patients may also need surgery to examine the gastrointestinal tract and remove any necrotic intestine. If the clot in the veins has not been dissolved with the thrombolytic therapy, the surgeon may need to directly remove clot from the mesenteric veins (mesenteric venous thrombectomy) at the time of operation. Patients will usually have a second operation to assess the gastrointestinal tract (second look laparotomy).

Visceral or mesenteric ischemia may also occur when there is no blockage in the arteries or veins supplying the gastrointestinal tract. In this disease known as nonocclusive mesenteric ischemia, there is a dramatic decrease in the arterial blood flow due to spasm or a reflex narrowing of the arteries supplying the intestines. Patients with this problem are often very ill from another major illness such as congestive heart failure or shock. In addition, the patient is often very dehydrated which may contribute to the poor blood flow to the intestine. The complaints are very similar to those in patients with acute embolic ischemia. The most common complaint is severe abdominal pain. The diagnosis is usually made with an x-ray of the mesenteric arteries, angiogram. The treatment of this problem involves giving the patient intravenous fluids and medications directed towards improving the blood flow to the gastrointestinal tract and other vital organs. In addition, medications which help relieve the spasm in the arteries, (vasodilatory agents) are given directly into the arteries supplying the intestines. These medicines are given to the patient through the same catheters used by the radiologist for the angiogram. The patient is then taken to surgery in order to examine the gastrointestinal tract and resect any necrotic intestine. A second operation to examine the gastrointestinal contents, second look laparotomy, may be performed 24 to 48 hours later.