An aneurysm, as defined by the Merck Manuals Online Medial Library, is an expansion, or a bulge, in the wall of a weakened artery. The most common occurrence of an arterial aneurysm is in the abdominal aorta, a condition called abdominal aortic aneurysm, or AAA. Abdominal aortic aneurysms may remain silent for years before they announce their presence through one of their serious complications.
Aortic Dissection
This is by far the complication with the most disastrous consequences. According to the Merck Manuals Online Medial Library, a dissection is when a small tear develops in the weakened internal wall of the artery. The pressure of the blood rushing between the layers of the wall of the artery may result in a rupture of the aneurysm. A complete rupture will cause internal bleeding that is life-threatening. The rupture of a dissecting aortic aneurysm may prove to be rapidly fatal, with no chance for resuscitative attempts. A small tear in the dissected wall is known as a "leak." This leak will cause severe abdominal pain that will prompt the patient to seek medical care. The risk of complete rupture of an abdominal aortic aneurysm is related to its size: the larger the aneurysm, the more likely it is to rupture.
Circulatory Thromboembolic Complications
MayoClinic.com notes that the blood flow in a dilated aortic wall is abnormal. This irregularity--sluggishness in the aneurismal part--gives the blood a chance to undergo the process of clotting, known as thrombosis. Parts of this blood clot may break loose and travel in the circulation to the lower limbs, where they can lodge in one of the arteries, cutting the limb's blood supply off, a process known as embolization. The compromise of the circulation to the lower limbs is called lower limb ischemia.
Complications Due to Pressure
There is another mechanism where an abdominal aortic aneurysm may block the circulation to the lower limbs. As explained by the Merck Manuals Online Medial Library, the abdominal aortic aneurysm involving a branch of the lower limb arteries may cause the blood flow to the legs to be reduced. Also, the aorta is located posteriorly in the abdomen, so when it enlarges due to an aneurysm, it compresses the vertebrae and causes intractable pain.
