Chapter 63

This chapter discusses aneurysms of the thoracic and abdominal aorta, and aneurysms of the iliac, popliteal, hepatic, renal, and splenic arteries.

An aneurysm is dilation of the arterial wall to >1.5 times its normal diameter. Aneurysms have been classically distinguished as true aneurysms, pseudoaneurysms, and mycotic aneurysms.

The wall of a true aneurysm consists of all layers of the vessel wall. Risk factors for such aneurysms include connective tissue disorders, familial history of aneurysm, and atherosclerotic risk factors (i.e., age, smoking, hypertension, and hyperlipidemia). A progressive decrease in elastin, collagen, and fibrolamellar units results in thinning of the media of the vascular wall and a decrease in its tensile strength. As the aorta dilates, the force on the aortic wall increases, which causes further aortic dilatation (Laplace law: wall tension = pressure × radius). The rate of aneurysmal dilatation is variable and predictable. Larger aneurysms expand more quickly than smaller ones. An average rate may be 0.25 to 0.5 cm/y.1 Patients with known aneurysms must be followed closely for unpredictably fast expansion.

The larger the aneurysm, the more likely it is to rupture. Once the stress on the vessel wall exceeds its tensile strength, it ruptures.

The wall of a pseudoaneurysm consists partly of the vessel wall and partly of fibrous or other surrounding tissue. A pseudoaneurysm can develop at the site of previous arterial catheterization or at anastomoses from prior vascular reconstruction, or can result from trauma or infection.2 Small pseudoaneurysms may eventually spontaneously thrombose.2

A mycotic aneurysm is an aneurysm that develops as a result of infection in the vessel wall. The source can be direct extension from a neighboring infection or embolization from valvular endocarditis. Mycotic aneurysms are more common in the immunosuppressed.

Peripheral and visceral aneurysms represent a small but important subset of arterial aneurysmal disease. Popliteal artery aneurysms are the most common peripheral aneurysm and are associated with both concomitant contralateral popliteal aneurysms and abdominal aortic aneurysms.3 True aneurysms and pseudoaneurysms of the femoral artery are uncommon and are associated with aneurysmal disease at other sites. Visceral artery aneurysms may occur anywhere but are most common in the renal, splenic, and hepatic arteries. Most visceral aneurysms remain silent and undetected until a complication such as rupture occurs. All but splenic artery aneurysms are more common in elderly men. Complications of aneurysms include rupture, which can be life-threatening, and thrombosis, which results in ischemia of vital organs and the distal extremities.4,5

Clinical signs and symptoms vary with the type of aneurysm and can be nonspecific or can be defined by the vessel’s location, or the pressure it exerts upon neighboring structures, or the signs of peripheral embolization from an intramural thrombus. Often diagnosis is made because an abdominal CT scan is performed for investigation of abdominal or flank complaints, or an extremity Doppler US examination is performed ...

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