There are two types of aortic aneurysm: thoracic aortic aneurysm and abdominal aortic aneurysm. Until recently, it was thought that thoracic aortic aneurysms and abdominal aortic aneurysms were due to the same cause. Now we know that the two types are separate diseases with different risk factors and causes.
The most common place for an aneurysm is the part of the aorta that runs through the abdomen, called the abdominal aorta. The abdominal aorta provides oxygen-rich blood to the tissues and organs of the abdomen and lower limbs.
A thoracic aortic aneurysm is a less common aneurysm that occurs in the chest portion of the aorta, above the diaphragm.
Why are aneurysms more common in the abdominal aorta than in the thoracic aorta?
Abdominal aortic aneurysms may be more common than thoracic aortic aneurysms because of the differences in the walls of the aorta in these two areas. The middle layer of the aortic wall contains muscle cells. This muscular layer of the wall is thicker in the thoracic aorta, which makes it stronger. Also, blood flows to this layer, which may contribute to its strength.