Monday, July 28, 2008

THORACIC AORTIC ANEURYSM

Aneurysms of the aorta in the chest are much less common
than abdominal aneurysms. They are classified as the
ascending, arch, or descending aortic aneurysms. Because
of the etiology and natural history, treatment differs for
each of these aortic segments. Aneurysms of the descending
thoracic aorta are the most common and have similar
causes as those of abdominal aneurysms. Aneurysms of
the descending aorta usually result from a cystic medial
necrosis; the etiology of which remains unknown. Also,
cystic medial necrosis is observed in nearly all cases of
Marfan syndrome. Another rare connective tissue disorder,
Ehlers-Danlos syndrome, may involve the aorta. Syphilis
was a common cause of ascending thoracic aneurysms,
but is now rare because aggressive antibiotic therapy cures
the disease in its early stages. In these cases chest x-ray
showed typical linear calcification of the dilated ascending
thoracic aorta.
A. Signs and Symptoms
More than 40% of patients are asymptomatic when first
diagnosed mainly by routine chest radiography. A large
ascending aortic aneurysm may compress the veins that
return blood from the head and neck to the heart via the
superior vena cava. The aneurysm of the aortic arch or
descending aorta may compress the trachea and cause
cough, shortness of breath, wheezing, and hemoptysis.
Posterior compression of the esophagus may cause difficulty
in swallowing and compression of the recurrent
laryngeal nerve may produce hoarseness. Pain in the back
and chest may occur; this is usually a constant deep, boring
pain that can sometimes be severe.
Diagnosis is usually obvious from the chest radiography
and aortography. A contrast-enhanced CT scan is
accurate in detecting and sizing thoracic aneurysms as
well as for monitoring growth. Magnetic resonance imaging
(MRI) is also useful.

B. Treatment
1. Medical
Because surgical therapy carries a high mortality rate and is
usually not advisable until ascending aneurysms are larger
than 5.5–6 cm or larger for descending aneurysms, medical
treatment has an important role. A beta-blocking drug is
strongly recommended to reduce dP/dt and for the control
of blood pressure. Beta-blockers reduce cardiac ejection
velocity and hydrodynamic stress. A randomized study of
70 patients with Marfan syndrome treated with propranolol
versus no beta-blocker and monitored over a 10-year
period showed the following: the treated group showed a
significantly lower rate of aortic dilatation, aortic dissection,
and aortic regurgitation; fewer deaths; aortic root
greater than 6 cm; and significantly lower mortality rates
from the 4-year point onward. This study shows that blood
pressure must be aggressively controlled.
2. Surgical
Significant risks are associated with thoracic aortic surgery,
particularly in the arch and descending aorta and surgery
is usually deferred for symptomatic patients or those
with aneurysms greater than 6 cm. Aneurysms are usually
resected and replaced with a prosthetic sleeve of appropriate
size. Postoperative complications include heart
attacks, heart failure, stroke, renal failure, respiratory
failure, and infection.

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