Mesenteric Ischemia can result from an arterial embolus (clot from another location), arterial thrombus, vasospasm (constriction of the blood vessels), or venous thrombosis. Vasospasm causing mesenteric ischemia is also called nonocclusive mesenteric ischemia (NOMI), since there is no clot within the arteries or veins. More than 50% of mesenteric ischemia is caused by an embolus (clot), usually from within the heart. The embolus lodges within the superior mesenteric artery (a main artery supplying the intestines) 50% of the time.
Thrombosis can also cause mesenteric ischemia in patients with atherosclerosis (plaque within the blood vessels). Vasospasm (NOMI) often occurs in very sick, hospitalized patients who are receiving “vasopressor” medications, which help to maintain a normal blood pressure. These medications constrict the blood vessels in the body to increase the blood pressure in patients with a low blood pressure. However, constricting the blood vessels can also prevent enough blood from reaching the mesentery and intestines, causing mesenteric ischemia.
The superior mesenteric vein is occluded in 95% of cases of mesenteric venous thrombosis. Some patients who develop mesenteric venous thrombosis have a blood clotting disorder, allowing blood to clot more easily.
What Are The Symptoms ?
If you have chronic mesenteric ischemia, you may experience severe pain in your abdomen 15 to 60 minutes after you eat. This pain can occur in any part of the abdomen, but most commonly it occurs in the middle to upper part. The pain may last for as long as 60 to 90 minutes and then disappear. Unfortunately, it tends to return the next time you eat. Many people with chronic mesenteric ischemia begin losing weight because, although they may feel hungry, they do not want to eat because they experience the pain.
Sometimes the symptoms of chronic mesenteric ischemia can be vague and can be similar to those of other conditions. Therefore, your physician will evaluate you and order tests to rule out other problems before making a definite diagnosis. In addition to abdominal pain and weight loss,
other symptoms that you might experience include:
What Causes Mesenteric Ischemia ?
Atherosclerosis, which slows the amount of blood flowing through your arteries, is a frequent cause of chronic mesenteric ischemia. Your arteries are normally smooth and unobstructed on the inside, but as you age, a sticky substance called plaque forms in the walls of your arteries. Plaque is made of fats and other materials circulating in your blood. As more plaque builds up, your arteries can narrow and stiffen. Eventually, enough plaque builds up to reduce blood flow through your arteries.
A clot, called an embolus, which travels to one of the mesenteric arteries and suddenly blocks the blood flow, is a common cause for acute mesenteric ischemia. These clots often originate in the heart and are more common among patients with an irregular heartbeat or Stent Surgery
Other conditions that may lead to mesenteric ischemia include:
- Low blood pressure
- Congestive heart failure
- Aortic dissection, which is a tear in the aorta's inner layer;
- Occlusion or blockage of the veins in the bowel;
- Coagulation disorders, or
- Unusual disorders of the blood vessels such as fibromuscular dysplasia and arteritits.
What Tests Will I Need ?
Your physician may perform several tests to rule out other conditions with similar symptoms. First your physician will ask you questions about your general health, medical history, and symptoms. In addition, your physician will conduct a physical examination. Together these are known as a patient history and exam. As part of your history and exam, your physician will ask you if you smoke or have high blood pressure. Your physician will also want to know when and how often your symptoms occur as well as how long you have been experiencing them.
After the history and exam, if your physician suspects you may have chronic or acute mesenteric ischemia, he or she may perform additional tests to evaluate your bowel and circulation, Arterial Bypass Surgery
- Angiogram. An angiogram (also called an arteriogram) is the test of choice, especially for acute mesenteric ischemia when rapid diagnosis is very important. An angiogram uses x-rays to view your body’s blood vessels. When the arteries are studied, the test is also called an arteriogram. To create the x-ray images, your physician will inject a dye through a thin, flexible tube, called a catheter, which is threaded into the desired artery from an access point. The access point is usually in your groin but it can also be in your arm. This dye, called contrast, makes blood vessels visible on an x-ray. In some circumstances, treatment through the catheter may also be started at the time of the angiogram.
- Doppler ultrasound. Doppler ultrasound uses high-frequency sound waves that bounce off of blood cells and blood vessels. This test can determine blood flow and show problems with the structure of blood vessels while it identifies specific arteries that are blocked. It takes some time to perform, however, and its accuracy may be limited by gas in the bowel.
- Blood test. When you have mesenteric ischemia, especially the acute variety, your white blood cells may be high. Blood tests may also show if acid in your blood is at high levels, a condition called acidosis. These findings may indicate the presence of serious bowel injury.
- Computed tomography (CT) scan. A CT scan creates detailed three-dimensional images from x-rays of slices of your body and can determine if there are problems with the arteries, such as aortic dissection, as well as with your other abdominal organs.
- Magnetic Resonance Angiogram (MRA) scan. A MRA scan also creates detailed three-dimensional images of your blood vessels from magnetic images of slices of your body. Its use is limited, however, if you have a metal implant in your body, such as a pacemaker or artificial hip.
How Is A Mesenteric Ischemia Treated ?
The goal of treatment for mesenteric ischemia (both chronic and acute) is to re-open the artery to allow adequate blood flow to reach your intestine to allow it to work properly. Because this must be accomplished before permanent damage is done to the bowel, depending on the situation, your vascular surgeon may treat mesenteric ischemia as an emergency or as a scheduled procedure.
For chronic mesenteric ischemia, one treatment method is trans-aortic endarterectomy, which is an operation that removes the plaque that blocks your mesenteric artery. To perform this procedure, a vascular surgeon makes an incision in your abdomen, or side, and then removes the plaque contained in the inner lining of the blocked mesenteric artery. Another treatment option for chronic mesenteric ischemia is bypass surgery. In bypass surgery, the surgeon creates a detour around a narrowed or blocked section of the artery. To create this bypass, your vascular surgeon can use one of your veins or sometimes a tube made from man-made materials can be used as an alternative. Your vascular surgeon attaches the bypass above and below the blocked area, producing a new path for blood to flow to your intestines. Your vascular surgeon will advise you what procedure is best for you on the basis of your particular situation.
Angioplasty and stenting is a newer method for opening a mesenteric artery and bracing it open to allow the blood to flow through. It can sometimes be performed at the time of the angiogram. In an angioplasty procedure, your vascular surgeon inflates a small balloon inside a narrowed mesenteric artery. After widening the artery with angioplasty, your vascular surgeon may insert a stent, which is a tiny metallic mesh tube that can support your artery’s walls to keep your vessel wide open.
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