Thoracic aortic aneurysms are described according to their location, size and shape. Location indicates the sections of the aorta affected (i.e., the root, ascending, arch, descending or thoracoabdominal). The size of the aneurysm is the diameter at the widest point of enlargement and is usually measured in centimeters. There are generally two different shapes for aneurysms: fusiform and saccular.

 As depicted in the drawing at the left, a fusiform aneurysm is enlarged equally in all directions. As an example, a diagnosis of an aortic aneurysm might be: a fusiform aneurysm of the ascending aorta, measuring 5.2 cm.

 The saccular aneurysm gets its name due to a bulge, or sack, occurring on only one side of the aorta, as pictured at the left.

A pseudoaneurysm is an aneurysm that does not have some or all of the aortic wall layers, often due to some injury to the inner aortic wall. They are also sometimes called false aneurysms. These aneurysms are more unpredictable, with a higher tendency to rupture at smaller sizes. Usually there is a greater inflammatory process involved in the surrounding tissue, which potentially can complicate a redo operation. Some pseudoaneurysms are the result of infection, which increases the risk of embolisation and stroke.