An arteriovenous malformation (AVM) is a congenital tangle of vessels in which arteries connect directly to veins without the normal capillary network. It can present with bleeding or seizures; treatment options include surgery, embolisation and radiosurgery.
What is an arteriovenous malformation (AVM)?
Normally, blood from the arteries passes through a network of capillaries, where its pressure falls, before reaching the veins. In an AVM, arteries connect directly to veins through an abnormal tangle of vessels called the "nidus". High-pressure blood passing straight into the veins strains the vessel walls and increases the risk of bleeding.
Brain AVMs are thought to be present from birth but usually cause symptoms in young adulthood. Some are found incidentally on imaging performed for other reasons.
Symptoms
- Sudden headache, vomiting and altered consciousness due to bleeding
- Seizures
- Recurrent headaches
- Weakness or numbness of an arm or leg, speech or visual disturbance
Diagnosis
MRI and MR angiography show the location of the AVM and its relationship to surrounding brain tissue. The feeding arteries, nidus and draining veins are assessed in detail with digital subtraction angiography (DSA). Grading systems based on the AVM's size, location and venous drainage are used in treatment planning.
Treatment Approach
- Microsurgery: For suitable AVMs in accessible areas, complete removal of the nidus eliminates the risk of bleeding immediately.
- Radiosurgery (Gamma Knife): Used for small and medium-sized AVMs, particularly in deep or critical areas. Radiation gradually thickens the vessel walls with the aim of closing the AVM. Closure usually occurs over a few years, during which the patient is followed with regular imaging.
- Embolisation: Through the blood vessels, the arteries feeding the AVM are blocked with special materials. It is used alone or as an adjunct before surgery or radiosurgery.
- Observation: For some AVMs that have not bled, observation may be preferred when the risks of treatment outweigh those of the natural course.