The need for oxygen
All organs of the body require oxygen and nutrients which are carried in the blood stream. If the flow of blood is interrupted for more than a few minutes, cells begin to die and damage occurs in that organ. A typical example would be a heart attack. A heart attack occurs when a blood clot causes a blockage in an artery in the heart. Part of the heart muscle dies and is replaced by scar tissue. Another example familiar to most people would be a stroke, or "brain attack." A stroke occurs when a blood clot causes a blockage in an artery in the brain. Part of the brain dies and paralysis often occurs.
Ischemic colitis - a "colon attack" Most people don't know that the same process can occur in the colon, or large intestine. This condition is called ischemic colitis. The word Ischemia means lack of blood. Colitis means inflammation of the colon. In people with ischemic colitis, a portion of the colon becomes inflamed and ulcerated due to a shortage of oxygen-rich blood. Ischemic colitis can be thought of somewhat like having a "stroke" in the colon. If blood flow to the colon is reduced sufficiently, damage occurs to the inner lining, or mucosa. If the damage is severe enough, the mucosa dies and is sloughed off leaving a crater, or ulcer.
The picture on the right is from a 72 year-old gentleman who came to our emergency room after having abdominal pain for two days. When the pain persisted and he developed bloody diarrhea, he decided he had better come to the hospital. His history and physical exam suggested ischemic colitis. A colonoscopy "scope" test was performed and showed severe ulceration of his upper left colon typical of ischemic colitis. In the picture above, the white material represents dead tissue that has been replaced by ulcers. (Compare the appearance to the photo on the left from a normal individual.) This patient was treated with antibiotics and medicines to prevent blood clots. After several weeks, the colon healed.
It's just plumbing To understand more about ischemic colitis, you must review some basic anatomy. It may be hard to believe, but the average adult digestive tract is about thirty feet long. The food goes down the esophagus (foodpipe) into the stomach pouch where acid digestion liquifies solids. The actual digestive process and absorption of nutrients occurs within the twenty feet or so of small intestine. The last six feet of the digestive tract is called the colon. It is here that waste water is purified and reabsorbed back into the blood stream.
Intestines can't feed themselves.
Even though our intestines process all the food that we eat, they cannot take nutrients or oxygen directly from that cheeseburger. Rather, like all other body organs, the intestines depend upon a constant flow of blood. The heart pumps this blood into the abdominal aorta, the main artery that enters the abdomen. The abdominal aorta has three side branches that carry blood directly to the digestive tract. Each has a different territory.
The celiac artery supplies the stomach and the upper part small intestine, or duodenum.
Superior Mesenteric Artery
The superior mesenteric artery (SMA) supplies blood to the rest of the small intestine and the right and mid-portion of the colon.
Inferior Mesenteric Artery
The inferior mesenteric artery (IMA), the smallest of the three and the one most often affected by "hardening of the arteries," supplies blood to the left side of the colon and the rectum.
Occlusive vs. Non-occlusive causes
In general, about 10% of the blood pumped out of the heart goes to the intestinal tract. But, the exact amount may vary from moment to moment. In cases of ischemic colitis, blood flow to a portion of the intestine is severely reduced for a while. Many factors may be responsible. Obviously, intestinal blood flow can be reduced by a physical blockage in the artery, like a blood clot. This is called occlusive disease.
However, in most cases, ischemic colitis is non-occlusive - meaning that there is no blood clot obstructing the flow of blood. Rather, there may be a temporary spasm of small blood vessels within the colon wall due to changes in heart rate, blood pressure, or various medications. This spasm, termed "vasoconstriction," may reduce blood flow enough to damage that portion of the colon.
The inside dies first
Whatever the cause, if blood flow is reduced for a long enough period of time, that portion of the colon will be damaged. However, the damage is not uniform. It mostly occurs on the more delicate inner lining.
The colon wall has an inner and outer covering. The tough outer layer is called the serosa. (Some sausage casing is made of intestinal serosa.) The "meat" of the wall, called the muscularis, is very resistant to ischemic damage. It is the delicate inner covering, called the mucosa, that is most vulnerable to ischemia. This is why most cases of ischemic colitis have damage only to the inner colonic mucosa.
Who is at risk?
Ischemic colitis is very much like coronary artery disease. Both conditions are caused by decreased blood flow - one in the heart, and the other in the colon. So, the risk factors for ischemic colitis are very similar to those of coronary heart disease: age over 50, smoking, high blood pressure, high cholesterol.
There has been some recent evidence that some patients with this problem suffer from an acquired or congenital abnormality in blood clotting called a "hypercoagulable condition." Blood clotting is an important body function. Like the "little Dutch boy," it seals an injury and stops the loss of blood. However, blood is not supposed to clot within the arteries and veins. If it does, it can block blood flow to an organ, such as the colon. Recent studies suggest that an underlying hypercoagulable condition may cause such blood clots and be the underlying cause of some cases of ischemic colitis. Occasionally, an individual will have an episode without any identifiable risk factors, just bad luck.
Symptoms of ischemic colitis
As cells begin to die and tissue dies, most patients know that something serious is wrong. They usually experience severe abdominal pain. After a while, bloody diarrhea with dark clots occurs. There may be nausea and vomiting.
How does the doctor know
An accurate diagnosis is the first step in treatment. The history of abdominal pain and bloody diarrhea raises suspicion. Despite the severe abdominal pain, there is often an unexpected lack of tenderness when the doctor examines the abdomen. Blood tests, CT scan x-rays are often helpful in making the diagnosis. If the diagnosis is still unclear, a limited colonoscopy exam may be requested to visualize the inner lining as in the case above.
If occlusive disease is suspected, an abdominal arteriogram may be suggested. This is an x-ray of the arteries in the abdomen, much like a cardiac catheterization. Here is an image taken from an abdominal arteriogram that demonstrates a focal narrowing at the origin of the SMA just as it leaves the aorta. This is an exomple of occlusive disease. If this narrowing was symptomatic and the causes of case of ischemic colitis, a balloon angioplasty might be performed to open up the narrowed segment. This is similar to the procedure done in patients with coronary heart disease.
Spontaneous recovery without treatment is the most frequent outcome. Mild cases may not even seek medical attention. Severe cases require hospitalization. Most inpatients are treated with IV fluids and are often administered antibiotics to lessen the chance of infection. Food is initially withheld to allow the intestines to rest for a few days. Most patients do quite well and are home in a few days. If they are anemic, they may be give iron pills for a month or so to help the body replace lost blood. If the colon ulcers were severe, prescription drugs like mesalamine (Asacol) may be prescribed to help the ulcers heal more quickly.
How about surgery?
Surgery is rarely necessary. In severe cases of acute disease and chronic strictures, however, surgical removal of the involved segement is safe and usually curative. If a focal narrowing is found in one of the three main arteries feeding the intestines, balloon angioplasty or surgical bypass might be indicated.
Can an attack be prevented?
There is no way to reliably prevent a repeat episode although most patients are placed on low dose daily aspirin to reduce blood clots. All tobacco products must be avoided. Over-the-counter cold remedies containing decongestants such as phenylephrine, phenylpropanolamine (also known as PPA), and pseudoephedrine should not be used. These ingredients produce a narrowing of blood vessels. This leads to clearing of nasal congestion, but it may also cause an decrease in blood flow. (These drugs can be identified if the small print warning on the box suggests that they not be taken by those with high blood pressure.) Anti-histamine-only preparations, like Coricidin HBP, are safe.