An aneurysm may occur when a part of an artery wall weakens causing it to widen or balloon out abnormally. It can occur anywhere, but usually, the common areas are:
major artery from the heart (aortic aneurysm)
the brain (cerebral aneurysm)
part of the leg behind the knee (popliteal artery aneurysm)
the intestine (mesenteric artery aneurysm)
an artery in the spleen (splenic artery aneurysm)