Arteriovenous malformations (AVMs) are defects in your vascular system. The vascular system includes arteries, veins, and capillaries. Arteries carry blood away from the heart to other organs; veins carry blood back to the heart. Capillaries connect the arteries and veins. An AVM is a snarled tangle of arteries and veins. They are connected to each other, with no capillaries. That interferes with the blood circulation in an organ.

AVMs can happen anywhere, but they are more common in the brain or spinal cord. Most people with brain or spinal cord AVMs have few, if any, major symptoms. Sometimes they can cause seizures or headaches.

AVMs are rare. The cause is not known, but they seem to develop during pregnancy or soon after birth. Doctors use imaging tests to detect them.

Medicines can help with the symptoms from AVMs. The greatest danger is hemorrhage. Treatment for AVMs can include surgery or focused radiation therapy. Because surgery can be risky, you and your doctor need to make a decision carefully.

NIH: National Institute of Neurological Disorders and Stroke