What causes arteriovenous malformation in the intestines? Is the blood loss dangerous? I was recently treated for anemia. Is there anything else I can do besides taking iron pills?

B.R.

Arteriovenous malformations (AVMs) are dilated, misshapen blood vessels located just underneath the inner lining of the stomach or the small or large intestines. In many people, they are thought to be present from birth and may be hereditary in such cases. In other people, they tend to appear with age, especially in the large intestine of patients with kidney failure.

No one is sure what causes AVMs. Often, they are discovered incidentally when a person undergoes an upper or lower endoscopy for other reasons. In such instances, no treatment is necessary.

In other cases, AVMs cause gastrointestinal (digestive tract) bleeding. The bleeding can be slow and lead to a gradual anemia over weeks to months, or can occur rapidly and cause intermittent, massive blood loss. Since AVMs are not a common cause of gastrointestinal bleeding and tend to be small (less than 5mm in most cases), they can be missed when an endoscopy is done to evaluate bleeding. Also, they often elude diagnosis because they can occur in the small intestine, a region that is difficult to examine during endoscopy.

When AVMs are detectable and thought to be the cause of gastrointestinal bleeding, they are treated with direct heat cautery -- a procedure in which the malformed blood vessels are burned and obliterated.

In many cases, the AVMs cannot be detected despite extensive testing, but are still thought to be the most likely cause of gastrointestinal bleeding. If the bleeding is rapid or frequent, it may be necessary to surgically remove the affected segments of intestine.

If the bleeding is slow, several other treatment approaches can be tried. Patients are often placed on iron pills to replace the iron lost in bleeding. Other therapies are used if iron tablets aren't enough to correct the anemia. In women, birth control pills are sometimes prescribed because the estrogen in the pills may reduce bleeding by causing regression of the AVMs or improving blood clotting. A new medication being used increasingly is octreotide (Sandostatin), a monthly injection that tends to reduce blood flow to the AVMs. Finally, some patients who continue to bleed and are not candidates for surgery may require periodic blood transfusions.