- Ascending aortic diameter > 4 cm on imaging study.
- Descending aortic diameter > 3.5 cm on imaging study.
In the ascending aorta, aneurysms tend to take on three common patterns, as indicated in Figure 35–1. These include the supracoronary aortic aneurysm, annuloaortic ectasia (marfanoid),
and tubular diffuse enlargement.
The three common patterns of ascending aortic aneurysm.
The most common pattern is that of supracoronary dilatation of the ascending aorta. In this pattern of disease, the short segment
of aorta between the aortic annulus and the coronary arteries remains normal in size. Sinuses are “preserved,” meaning that the aorta indents normally, forming a “waist,” near the level of the coronary arteries. For this type of aneurysm, a supracoronary tube graft suffices.
In the second type, annuloaortic ectasia, the aortic annulus itself becomes dilated, giving a shape to the aorta like an Erlenmeyer
chemistry flask. In this type of disease, the segment of aorta between
the annulus and the coronary arteries is diseased, dilated, and
thinned. Sinuses are “effaced,” meaning that the
normal indentation, or waist, is lost. When surgery is required,
the entire aortic root must be replaced.
In the third type of ascending aortic disease, the configuration is midway between the previous two patterns, that is, there is some
dilatation of the annulus and root and some effacement of the sinuses,
but these elements are not dramatic. The overall appearance is that
of a large tube, rather than a flask. For such aortas, either supracoronary
tube grafting or aortic root replacement may be appropriate.
The Crawford classification (Figure 35–2) is used to categorize the appearance of an aneurysm in the descending aorta and thoracoabdominal aorta. This classification is based on the longitudinal location and extent of aortic involvement and has implications for surgical strategy and affects the risk of perioperative complications.
The Crawford classification of descending and thoracoabdominal aneurysms. See text for description of each type.
(Reprinted, with permission, from Edmunds LH Jr, ed. Cardiac Surgery in the Adult. New York: McGraw-Hill, 1997.)
Type I aneurysms involve most of the thoracic aorta and the upper abdominal aorta. Type II aneurysms, the most extensive and most dangerous to repair, involve the entire descending and abdominal aortas. Type III aneurysms involve the lower thoracic and abdominal aortas. Type IV aneurysms are predominantly abdominal but involve thoracoabdominal exposure because of the proximity of the upper border to the diaphragm.
The genetics of Marfan disease, a well-known cause of aneurysms of the thoracic aorta, have been well delineated, with over 85 mutations
identified at one locus on the fibrillin gene.
Increasingly, it is being appreciated that patients who do not have Marfan disease also manifest familial clustering of thoracic
aortic aneurysms and dissections. Patients with aneurysms often
answer one or both of the following questions affirmatively: “Do
you have any family members with aneurysms anywhere in their bodies?
Did any of your relatives die suddenly or unexpectedly of apparent
cardiac causes?” Detailed construction of family trees
on over 500 patients with thoracic aneurysm have indicated that
21% of aneurysm probands have a first-degree relative with
a known or likely aortic aneurysm. The true number is certainly much higher, as these estimates are based only on family interview and not on head-to-toe imaging of relatives. Figure 35–3 shows the 21 positive family trees of the first 100 families analyzed. The most likely pattern of inheritance appears to be autosomal-dominant with incomplete penetrance. A most recent analysis has shown that the location of the proband’s aneurysm
largely influences the location of the aneurysms in the family members. If
the proband has an ascending aneurysm, the likelihood is that the
family members have ascending aneurysms. If, however, the proband
has a descending aneurysm, it is likely that the family members
have abdominal aortic aneurysms. These proband-family member observations
are in keeping with the general concept that aneurysm disease divides
at the ligamentum arteriosum: Ascending and arch aneurysms represent
one disease, largely nonarteriosclerotic, while descending and abdominal
aneurysms represent another disease, largely arteriosclerotic.
The 21 positive family trees among the first 100 families assessed for genetic patterns of thoracic aortic disease.
Application of modern molecular genetic techniques is successfully making progress toward determining the specific genetic aberrations
responsible for these family clusterings and for thoracic aneurysms
in general. Specific sites of genetic mutations that underlie many
of the instances of familial inheritance, including the so-called
TAAD1 (Thoracic Aortic Aneurysm and Dissection 1) locus, has been
uncovered. Examination of single nucleotide polymorphisms (SNPs)
in the blood of hundreds of patients with thoracic aortic aneurysms
via genome-wide surveys using large (> 30,000) SNP libraries has
been examined. An “RNA signature” in the blood
of patients with thoracic aortic aneurysm was found, which can predict
with about 85% accuracy from a blood test alone whether
the patient harbors a thoracic aortic aneurysm. This “signature” is
composed of specific RNAs that are either markedly up-regulated or markedly down-regulated in aneurysm patients, compared with healthy controls. These RNA profiles reflect alterations in RNA expression brought about by the aneurysm disease. The corresponding analyses of DNA polymorphisms, which would reflect the underlying mutations in the genome, is nearing fruition.
Patients who have a genetic predisposition for aneurysm development, specifically those patients with annuloaortic ectasia or ascending dissection, are significantly protected from arteriosclerosis (Figure 35–4). It appears likely that the same mutations that promote lysis of the aortic wall also prevent ...