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