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
is performed in a search for deep venous thrombosis. Once rupture
has occurred, regardless of the location of the aneurysm, hemorrhagic
shock develops, and mortality is certain without surgical intervention.
An abdominal aortic aneurysm is defined as an aneurysm
≥3.0 cm in diameter, and repair is considered for an aneurysm ≥5.0
cm in diameter. Abdominal aortic aneurysms have a clear familial
trend. Eighteen percent of patients with abdominal aortic aneurysm
have a first-degree relative with an aortic aneurysm, compared with
<3% of those without aneurysm. Most patients are >60
years old, and males have an increased risk of the disease. Patients
with aneurysms involving other major arteries and those with peripheral
arterial disease are also at increased risk for aortic aneurysmal
disease. The risk increases with the number of years of smoking
and decreases with the number of years since quitting smoking.6
Symptomatic abdominal aortic aneurysms may present with a variety
of signs or symptoms that can mimic other primary diagnoses: syncope;
flank, back, or abdominal pain; GI bleeding from an aortoduodenal
fistula; extremity ischemia from embolization of a thrombus in the
aneurysm; shock; or sudden death. Sudden death most commonly occurs
from intraperitoneal rupture of the aneurysm, which leads to massive,
rapid blood loss and certain mortality. Syncope without warning
symptoms followed by severe abdominal or back pain suggests rupture
of an abdominal aortic or visceral aneurysm. Syncope is caused by
rapid blood loss and a lack of cerebral perfusion. Patients may
temporarily regain consciousness, but irreversible hemorrhagic shock
follows without prompt diagnosis and intervention.
In general, back or abdominal pain is the most common presenting
symptom. The pain is often described as severe and abrupt in onset.
About half of patients describe a ripping or tearing pain.7 Syncope
may be present in about 10%. Many patients present with
atypical sites of pain: flank, groin, isolated quadrants of the
abdomen, and hip. Other common symptoms, such as nausea, vomiting,
bladder pain, hip pain, or tenesmus, may complicate the presentation.
Physical examination has only a moderate ability to detect a
large abdominal aortic aneurysm. The sensitivity of abdominal palpation
increases significantly with aortic aneurysm diameter, ranging from
29% for a diameter of 3.0 to 3.9 cm to 50% for
a diameter of 4.0 to 4.9 cm and 76% for a diameter of ≥5.0
cm.8 Tenderness to palpation of an aneurysm is
commonly interpreted as a sign of aneurysmal expansion or rupture. However,
a lack of tenderness does not indicate an intact aorta. Examination
is difficult in the very obese and the very thin. It is generally
impossible to identify an aneurysm on physical examination in those
with an obese abdomen. Very thin patients may have an aorta that
is easily palpable, but is not aneurysmal.
The differential diagnoses for abdominal aortic aneurysm include
the causes of syncope, abdominal pain, chest pain, back pain, and
shock. The presentation of syncope with back pain or shock ...