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Accurate, early diagnosis of brain aneurysm is critical, but aneurysms usually have no symptoms until they bleed. Similarly, most people with arteriovenous malformation (AVM) experience few or no symptoms until the AVM ruptures and bleeds.

Occasionally, these abnormalities can press on the brain or on the nerves stemming out of the brain and cause neurological symptoms without bleeding. 

Symptoms of a ruptured aneurysm or AVM may include: 

  • Severe, sudden headache, described as "the worst headache of my life"
  • Neck stiffness
  • Sensitivity to light
  • Nausea and vomiting
  • Loss of consciousness
  • Seizures

When this bleeding occurs, most people realize that something is wrong and go to a hospital emergency room. 

Usually patients need a combination of tests to provide information for diagnosis and treatment.

This noninvasive X-ray is usually the first test ordered when an aneurysm or AVM rupture is suspected. It shows blood that escaped from the rupture.

MRI is a radiology test that uses a magnetic field to show a detailed, three-dimensional view of the brain. MRI shows the aneurysms and AVMs better than the CT scan.

This procedure provides the best pictures of arteries of the brain and the aneurysm or AVM’s exact location. It may follow a CT scan or MRI.

An interventional neuroradiologist (a doctor who specializes in interpreting images of the brain, spine and nerves) conducts the angiogram. The patient is awake, with a mild sedative to relax.

The doctor threads a hollow tube (catheter) from an artery in the groin to the main arteries in the neck that supply the brain. Dye is injected, then an X-ray camera takes pictures of the brain's arteries. The aneurysm shows up as a dilated area on an artery. The AVM shows up as bundle of arteries and veins.

Magnetic resonance angiography (MRA) and CT angiography (CTA) are less invasive tests than the cerebral angiogram. Instead of a catheter, they use an injection of dye and MRI or CT scanning.

The tests provide an indirect picture of the brain's arteries. The MRA and CTA may not show small aneurysms or AVMs and do not match the angiogram's higher-quality images.

This test, also called a spinal tap, collects spinal fluid to check for blood and to measure pressures. A needle is inserted between two vertebrae in the back, and spinal fluid is drawn out.