418
U N I T 5
Circulatory Function
(<4 cm in diameter) to 11% per year for aneurysms
larger than 5 cm in diameter.
1
Thoracic aneurysms, which are less common than
abdominal aortic aneurysms, may involve one or more
aortic segments. Most thoracic aneurysms are due to
atherosclerosis. Disorders of connective tissue, such as
Marfan syndrome (Chapter 6), are rare causes but of
important clinical significance. The majority of thoracic
aneurysms are asymptomatic. When symptoms occur,
they depend largely on the size and position of the aneu-
rysm. Substernal, back, or neck pain may occur. There
may be dyspnea, stridor, or a brassy cough caused by
pressure on the trachea. Hoarseness may result from
pressure on the recurrent laryngeal nerve, and there
may be difficulty swallowing because of pressure on
the esophagus.
23
The aneurysm also may compress the
superior vena cava, causing distention of neck veins and
edema of the face and neck.
Abdominal aortic aneurysms, which are the most
common type of aneurysm, usually develop after age
50 and are associated with severe atherosclerosis. They
occur more frequently in men than women, and over
half of affected persons are hypertensive. Although
abdominal aortic aneurysms usually occur in the con-
text of atherosclerosis, it is thought that other factors
such as smoking and a genetic predisposition may play
a role.
2,24
Abdominal aortic aneurysms are most commonly
located below the level of the renal artery (>90%) and
involve the bifurcation of the aorta and proximal end of
the common iliac arteries.
1,2
They can involve any part
of the vessel circumference (saccular) or extend to involve
the entire circumference (fusiform). Most abdominal
aneurysms are asymptomatic. Because an aneurysm is
of arterial origin, a pulsating mass may provide the first
evidence of the disorder. Typically, aneurysms larger than
4 cm are palpable. The mass may be discovered dur-
ing a routine physical examination or the affected per-
son may complain of its presence. Calcification, which
frequently exists on the wall of the aneurysm, may be
detected during abdominal radiologic examination.
Pain may be present and varies from mild midabdomi-
nal or lumbar discomfort to severe abdominal and back
pain. As the aneurysm expands, it may compress the
lumbar nerve roots, causing lower back pain that radi-
ates to the posterior aspects of the legs. The aneurysm
may extend to and impinge on the renal, iliac, or mes-
enteric arteries, or to the vertebral arteries that supply
the spinal cord. An abdominal aneurysm also may cause
erosion of vertebrae. Stasis of blood favors thrombus
formation along the wall of the vessel (Fig. 18-11), and
peripheral emboli may develop, causing symptomatic
arterial insufficiency.
Diagnostic methods include ultrasonography,
echocardiography, CT scans, and MRI. Unruptured
aneurysms are generally asymptomatic and are often
diagnosed incidentally during clinical examina-
tion. Measures to slow aneurysm growth and lower
the risk of rupture include risk factor modification.
Hypercholesterolemia and high blood pressure should
be controlled and smoking discontinued. Surgical repair,
in which the involved section of the aorta is replaced
with a synthetic graft of woven Dacron, frequently is
the treatment of choice.
23,24
Aortic Dissection
Aortic dissection (dissecting aneurysm) is an acute, life-
threatening condition.
1,2,28
It involves hemorrhage into
the vessel wall with longitudinal tearing of the vessel
wall to form a blood-filled channel (see Fig. 18-10B).
Unlike atherosclerotic aneurysms, aortic dissection
often occurs without evidence of previous vessel dila-
tion. The dissection can originate anywhere along the
length of the aorta but most often involves the ascend-
ing aorta.
Aortic dissection is caused by conditions that weaken
or cause degenerative changes in the elastic and smooth
muscle layers of the aorta. There are two risk factors
that predispose to aortic dissection: hypertension and
degeneration of the medial layer of the vessel wall. It is
most common in 40- to 60-year-old men with an ante-
cedent history of hypertension.
1
Aortic dissection also
is associated with connective tissue diseases, such as
FIGURE 18-11.
Atherosclerotic aneurysm of the abdominal
aorta.The aneurysm has been opened longitudinally to reveal
a large thrombus in the lumen.The aorta and common iliac
arteries display complicated lesions of atherosclerosis. (From
Gotlieb AI, Lui A. Blood vessels. In: Rubin R, Strayer DS, eds.
Rubin’s Pathology: Clinicopathologic Foundations of Medicine,
6th ed. Philadelphia, PA: Wolters Kluwer Health/Lippincott
Williams &Wilkins; 2012:471.)
