Diagnostic ultrasound ( PDFDrive )

CHAPTER 12 The Retroperitoneum 433
disease, when considered separately from other cardiovascular
diseases, was still by far the single leading cause of death (370,213
deaths) in the United States. 2 Stroke, when considered separately
from other cardiovascular diseases, was the underlying cause
for 128,978 deaths in 2013. 2 By 2013, stroke had dropped to
become the ith leading cause of death, ranking behind heart
disease, cancer, chronic lower respiratory diseases, and unintentional
injuries in that order. 2
Atherosclerosis is a complex process. Current understanding
of its pathogenesis views atherosclerosis as a chronic inlammatory
response triggered by injury to the endothelium. he endothelial
injury results in increased permeability of the intima, allowing
accumulation of low-density lipoprotein into the arterial wall.
Inlammation results and plaque is produced, consisting of lipids,
smooth muscle cells, ibrous tissue, macrophages, and calcium
within the arterial wall. 1 Hemorrhage may also be present within
the plaque. Atherosclerotic plaque can cause decreased blood
low to target organs by narrowing the arterial lumen, which
can result in ischemic signs and symptoms such as claudication
and erectile dysfunction (aortoiliac disease), hypertension and
renal insuiciency (renal artery disease), and mesenteric ischemia
(mesenteric artery disease).
Although there is controversy, many researchers believe that
the processes inherent in atherosclerosis contribute to aneurysm
formation. 3 Other, less common causes of aneurysms include
cystic medial necrosis, trauma, and infection. 1
ABDOMINAL AORTIC ANEURYSM
he abdominal aorta slowly tapers from the diaphragmatic hiatus
to the aortic bifurcation (Fig. 12.1). Most of the tapering occurs
in the proximal abdominal aorta as its largest branches (celiac,
FIG. 12.1 Abdominal Aorta Anatomy. The abdominal aorta tapers
from the aortic hiatus to the aortic bifurcation. The greatest tapering
occurs as the aorta gives off its largest branches: the celiac, superior
mesenteric, and renal arteries.
superior mesenteric, and renal arteries) arise. he normal size
of the supraceliac abdominal aorta ranges from 2.5 to 2.7 cm in
men and 2.1 to 2.3 cm in women. he normal diameter of the
infrarenal aorta ranges from 2.0 to 2.4 cm in men and 1.7 to
2.2 cm in women. 4
Mortality
Abdominal aortic aneurysm (AAA) is a common disease in
the older population. Annually, 40,000 patients undergo elective
repair in the United States. 5 AAA rupture is a catastrophic event.
Many patients with ruptured aneurysms die before reaching a
hospital. Of those admitted with rupture, many do not survive
to go to surgery. For those with ruptured AAA that make it to
surgery, the operative mortality rate is decreasing. Statistics from
2010 show an operative mortality rate of 33.4% for open procedures,
a decrease of 10.1% from 2000. 5 When endovascular repair
is used, the mortality rate is even lower—19.8% in 2010. 5 he
overall mortality rate of a ruptured AAA is reported as being
85% to 90%, 6 largely because many patients with aortic rupture
never make it to the operating room. Mortality for those undergoing
elective repair in 2010 was 0.9% for endovascular repair and
4.8% for those undergoing open repair. 5 hese facts suggest that
the majority of deaths from AAA ruptures are preventable.
Much research has been conducted on reducing the number
of deaths caused by AAAs. Ultrasound screening has proved to
be a cost-efective step. Medical therapies may reduce the rate
of growth of AAAs once they are detected. For large aneurysms,
open or endovascular repair is much safer when done electively
than emergently. With this knowledge, the AAA mortality rate
can be greatly reduced.
Deinition
here are many deinitions of an arterial aneurysm. 7 A general
deinition is an increase in the diameter of an artery of at least
50% compared to the normal diameter of that artery. 4 For example,
if a patient has an aorta that measures 2.2 cm in diameter, the
aorta would be classiied as aneurysmal at 3.3 cm. his deinition
can be diicult to apply to an abdominal aorta because it may
not be clear what constitutes the normal aortic diameter in a
speciic patient.
he majority of AAAs are infrarenal. he most practical and
common deinition of infrarenal AAA speciies that an aneurysm
is present when the infrarenal aorta has a diameter of 3.0 cm or
greater. Aortas can also be referred to as subaneurysmal when
they measure between 2.5 and 2.9 cm. 8 Subaneurysmal aortas
have about a 50% chance of developing into a true aneurysm at
5 years. 9
he deinition that an AAA is present if the infrarenal aorta
measures 3.0 cm or greater works well in most situations. However,
the deinition can be insuicient, particularly in small patients.
It should be remembered that an aorta measuring 2.5 cm in
diameter is properly called aneurysmal in a patient who has a
more proximal aortic diameter measuring 1.6 cm.
Aneurysms that involve the renal arteries or the suprarenal
aorta are less common and oten occur with an aneurysmal
thoracic aorta. AAAs that occur at or above the renal arteries
are included in the Crawford classiication of thoracoabdominal