DISEASES OF BOTH THE ARTERIES AND THE VEINS
An uncommon problem with blood vessels is a malformation in which arteries and veins are directly connected, instead of being joined by capillaries. This can take two general forms: arteriovenous malformation, which is a congenital condition, and arteriovenous fistula, which is usually the result of trauma.Arteriovenous malformations are “tangles” of small arterial vessels that are intertwined with small veins. The blood from the arteries flows directly into the veins. These malformations can be present anywhere in the body and in any organ. The consequences of having an arteriovenous malformation depend on their location and size. A small one in the brain may produce more problems than a larger one in the liver, for example.A fistula can be thought of as a window or conduit that directly connects a large artery with a large vein. This might occur if a person receives a puncture wound that penetrates through an artery and vein that lie next to each other. Even after the healing process occurs, a connecting pathway between the two vessels may remain. Some blood from the artery may be diverted (shunted) directly into the vein before it goes to the capillaries. If a fistula (or arteriovenous malformation) is large, the blood flow through it may be very high. If so, the heart works excessively hard to keep up with the needs of the body.Some arteriovenous malformations can be fixed by blocking the artery from which they branch. This can occasionally be done by inserting a special small balloon or other material directly into the artery with a catheter.*215\252\8*
