Abdominal aorta aneurysms may be classified according to several factors.

Classification based on shape

The commonest classification that is used is based on the shape of the bulge or the lesion.

This classification includes:-

• Saccular aneurysms are asymmetrical and appear on one side of the aorta. They are usually caused by injury or a severe aortic ulcer.
• Fusiform aneurysms appear as symmetrical bulges around the circumference of the aorta. This is the commonest shape of an aneurysm.

Un-ruptured and ruptured aneurysms

Another classification divides aneurysms into un-ruptured and ruptured aneurysms.

Unruptured abdominal aortic aneurysm

This is the more common form of aortic aneurysm. This may be a co-incidental finding on clinical examination, or on scans - ultrasound, CT or MRI conducted for some other indication. Possible symptoms include pain in the loins, back or navel. Back pain may be caused by the pressure of the aneurysm on the vertebrae and spinal cord.

On examination a pulsating mass may be felt in the abdomen. Fibrosis and adhesions may occur around the aneurysm leading to compression of structures of the abdomen like intestines etc.

Ruptured abdominal aortic aneurysm

This is considered among patients with severe fall in blood pressure. There is severe pain in the abdomen, back or loin that is sudden in onset. With severe fall in blood pressure there may be intense sweating, shock, collapse and black out.

Death occurs in 85 to 95% cases unless the patient is transferred to the hospital immediately and bleeding is stopped.

A dissecting aneurysm

This is also known as an aortic dissection is seen when a tear develops in the inner layer of the wall of the aorta. This leads to separation of the layers of the wall of the aorta and further weakens the wall of the aorta.

Classification according to size

Yet another way of classifying abdominal aortic aneurysms is according to their size. An aneurysm is usually defined as an outer aortic diameter over 3 cm (normal diameter of aorta is around 2 cm).