An intracranial arteriovenous malformation (AVM) is a tangle of arteries and veins that short-circuits normal blood flow. Because the walls of these vessels are thinner than usual, they can leak or burst, producing symptoms that range from quiet warnings to sudden emergencies.

The most dramatic first sign is a sudden, severe headache—often described as a “thunderclap” that hits in seconds. It may be followed by nausea, vomiting, stiff neck, or loss of consciousness if the AVM bleeds.

Seizures are another common clue. A person may jerk, stare blankly, or black out for a few minutes, even with no history of epilepsy. These spells can occur weeks or years before any bleed.

Gradual headaches that feel like pressure or pounding behind one eye are frequent in the lead-up. Bending over, coughing, or straining can make the pain spike.

Vision or speech can flicker. Transient blurry sight, trouble finding words, or numbness on one side of the face or body may last minutes and then vanish, mimicking a mini-stroke.

Some people hear an internal “whoosh” that keeps time with their heartbeat, especially at night. Laying the head flat or turning to one side can make the noise louder.

Fatigue or mood swings sometimes appear if the AVM steals blood from surrounding healthy brain tissue. Concentration fades quickly, or family notice irritability without obvious cause.