Arteriovenous malformations (AVMs) are defects in your circulatory system. The circulatory system includes the arteries, veins and capillaries that carry blood to and from the heart. An AVM is a snarled tangle of arteries and veins. It interferes with the blood circulation in an organ. AVMs can happen anywhere, but the ones located in the brain or spinal cord can have effects such as seizures or headaches. However, most people with brain and spinal cord AVMs experience few, if any, significant symptoms.
NIH: National Institute of Neurological Disorders and Stroke