What you need to know about these uncommon but much-feared blood vessel abnormalities.
Each year, tens of thousands of people discover they have a bulging blood vessel in their brain, chest, or abdomen. Known as aneurysms, these bulges or balloon-like pouches form at a weak spot along an artery. The most common — and most dangerous — are in the brain or along the body's largest blood vessel, the aorta (see illustration).
Because aneurysms are uncommon, doctors don't screen for them routinely. Most are found by accident during tests such as an ultrasound or MRI scan done for other reasons. Of course, some aren't discovered until they leak or burst, often without any warning signs. The potentially fatal consequences of that bleeding explain why most people associate aneurysms with a sense of dread. However, understanding the underlying causes can help you prevent them and know whether you should undergo any screening tests.