Dural arteriovenous fistulas are direct connections between arteries and veins within the dura mater (the tissue which covers the central nervous system). Symptoms may include tinnitus, dizziness, headache, or symptoms around one eye, such as cranial nerve palsies or protrusion of an eyeball. In the case of a spinal fistula are the most common symptoms are progressive weakness of the legs. Even non-symptomatic fistulas may include a risk of bleeding. The hemorrhage can occur into the brain or into the spaces outside the brain. Treatment is by operative disconnection of the fistula or by endovascular embolization.