An arteriovenous malformation occurs when arteries and veins develop in ways that form a tangle. The tangled arteries and veins of arteriovenous malformations also form abnormal connections between them that impair normal blood flow and oxygenation to surrounding tissues. Arteriovenous malformations most commonly form in the brain or spinal cord but may also appear elsewhere in the body. Some types of arteriovenous malformations may resemble birthmarks called hemangiomas or port-wine stains. Arteriovenous malformations can rupture and cause bleeding.

Arteriovenous malformations may not cause any initial symptoms and are often only discovered after they have ruptured or during an examination or imaging for another health concern. Symptoms of an arteriovenous malformation depend on where it is located. Symptoms may not appear until after the arteriovenous malformation has ruptured and caused bleeding. Symptoms of an arteriovenous malformation may include headache; nausea; dizziness; seizures; loss of neurological function; confusion; cognitive difficulties; learning or behavioral difficulties in children and teens; loss of consciousness; vision problems; buzzing sounds in the ears; speech difficulties or difficulty understanding language (aphasia); memory loss or dementia; hallucinations; weakened muscles; partial paralysis; facial paralysis; drooping eyelids; changes in sense of smell; difficulty with balance and walking; coldness in fingers and toes; and back pain. A particular type of arteriovenous malformation called a vein of Galen defect may cause symptoms at birth, including fluid on the brain (hydrocephalus); swollen scalp veins; seizures; failure to thrive; and congestive heart failure.

Treatment for arteriovenous malformation depends on its location and symptoms. Some arteriovenous malformations may be managed with a watch-and-wait approach and regular imaging. Arteriovenous malformations that have bled, are causing other symptoms, or that are in a part of the brain that can be safely treated may require surgery. Endovascular surgery is a minimally-invasive approach to treating arteriovenous malformations in which a catheter is inserted into an artery into which a substance such as a medical glue is injected, or a metal coil is placed, to stop or reduce blood. Stereotactic radiosurgery is also used with focused beams of radiation that stop the blood supply to the arteriovenous malformation. Sclerotherapy is when a liquid medicine is injected into the arteriovenous malformation to reduce its blood flow. Medications to manage the symptoms of arteriovenous malformations, such as seizures or headaches, may also be given.