A brain aneurysm is a weakening of the wall of an artery inside your brain. Over time, the pressure inside the artery causes it to balloon out. Small brain aneurysms do not cause symptoms. You may have one and not know it. A bigger aneurysm, though, may cause symptoms. These may include headache or pain behind your eye, weakness and numbness, or changes in your vision. A brain aneurysm that ruptures and bleeds causes sudden symptoms. These may include a very severe headache, nausea and vomiting, weakness and numbness, stiff neck, and loss of consciousness. Doctors use imaging studies of your brain to check for an aneurysm. Your doctor may order one of these studies if you have symptoms of a brain aneurysm. You may have imaging tests even if you don't have symptoms if a parent or sibling has had an aneurysm. That would be a screening exam. Your doctor may also recommend screening if more than one family member has had a brain aneurysm. Most people don't get screened until they are older than 25. Tests to Diagnose an Aneurysm The type of test your doctor orders will depend on the reason for the test: CT scan (computed tomography). This simple test is quick and painless. You lie on a table while multiple X-rays go into a computer to make images of your brain. This test may be the first test for screening. MRI (magnetic resonance imaging). This is also a simple test. It takes longer than a CT scan, though. You lie on a table while magnetic signals go through your brain. A computer organizes the signals into brain images. CT or MRI angiography. If your doctor wants a more detailed image of your brain, you may have a special dye injected into one of your blood vessels before you have a CT or MRI. The dye flows to your brain and makes it much easier to see the network of blood vessels. This test helps find smaller aneurysms and any bleeding. Diagnostic cerebral angiogram. This is the most reliable diagnostic test. You would have this test to confirm a diagnosis of a brain aneurysm before any treatment. Your doctor makes a small incision in your groin. The doctor inserts a long, thin tube (catheter) into an artery and moves it along until it reaches arteries that go directly into your brain. Dye is injected, and X-rays are taken. Cerebrospinal fluid study. This is not an imaging study. Your doctor may order this test if he or she suspects bleeding in your brain. The doctor places a thin needle through your lower back into your spine. This lets the doctor check the fluid around your spinal cord and brain to look for bleeding. Next Steps for Treatment If your doctor diagnoses a brain aneurysm, the next steps depend on many factors. A bleeding aneurysm almost always needs immediate surgery. Your doctor also may recommend surgery if you have an aneurysm that is likely to bleed. If you have a small aneurysm without much risk of bleeding, your doctor may recommend "watchful waiting." You would have imaging studies done every so often. As long as your aneurysm is not getting bigger, you would not need treatment.