What is it?
An aneurysm is a blood-filled balloon-like bulge in the wall of a blood vessel. It can occur in any blood vessel, including the brain and heart. When an aneurysm gets bigger the chance of its rupturing increases, and if it ruptures, the result can be internal bleeding.
It is estimated that there is a 2-3% prevalence of brain aneurysms in people without risk factors.
What causes it?
Risk factors for developing an aneurysm include diabetes, obesity, high blood pressure, smoking, and alcoholism. The risk also gets higher with age.
What happens during it?
There are, in fact, two different types of aneurysms. The first is called a true aneurysm. It happens when all the layers of the blood vessel wall expand so that the diameter of the vessel also becomes bigger in that spot.
The expansion of the vessel wall is caused by its weakening. That’s why basically anything that weakens the wall can lead to an aneurysm. When a blood vessel wall is weaker than it’s supposed to be, it struggles to cope with the pressure of the blood continuously pushing it. Slowly the wall gives in and the vessel starts to dilate.
This weakening can happen if the cells in the vessel walls don’t get enough oxygen. In most vessels the cells are able to just take the oxygen from the blood flowing through them, but in some places like the aorta where the walls are very thick, the wall cells need to have their own little blood vessels flowing among them and supplying them with oxygen. These tiny vessels can become too narrow as a result of, for example, high blood pressure. They aren’t able to provide the wall cells with enough oxygen, and just as your muscles start to feel weak if you run really fast for a while, so the wall also becomes weak. Atherosclerosis can also lead to this weakening for the simple reason that the oxygen can’t get to the vessel walls through the fatty build-ups. Some pople with connective tissue diseases, such as Marfan syndrome, are also at a higher risk of aneurysms because their bodies don’t produce enough of the proteins that are supposed to make the vessel walls stronger.
The second type of aneurysm is called a pseudoaneurysm. In this case, the blood vessel itself hasn’t actually dilated. Blood has leaked out of it, and the surrounding tissue holds it in one place.
How can it be treated?
For a long time the only treatment options for aneurysms were surgery and just “seeing how it goes”. Now there are thankfully more options. A brain aneurysm can be treated through either surgically getting to the aneurysm and then closing its base with a clip, or through passing a catheter with the bloodstream all the way to the brain so that the platinum coils cause the blood in the aneurysm to clot. Aneurysms in the heart or elsewhere in the body can be treated through removing the weakened part of the blood vessel and inserting a new, stronger part there instead.
Sources: en.wikipedia.org/wiki/Aneurysm (and the WebMD video on the page)