Coiling is a minimally invasive endovascular procedure performed to treat an aneurysm – a balloon-like bulge or weakening of an artery wall. As an aneurysm grows, it thins and weakens. It can become so thin that it leaks or ruptures, releasing blood into the space around the brain. This bleeding is called a subarachnoid hemorrhage (SAH) and is life threatening. During coiling, tiny coils are packed into the aneurysm to promote blood clotting and close off the aneurysm.