The risk for rupture is related to the size of AAAs. Those 4 cm or less in diameter almost never burst, while those between 4 and 5 cm do so at a rate of 1% per year. The risk rises to 11% per year for AAAs 5 to 6 cm in diameter, and to 25% per year for aneurysms greater than 6 cm in diameter. Thus, aneurysms 5 cm in diameter or larger are managed surgically, either by open placement of tubular prosthetic grafts or with endoluminal insertion of stented grafts (expandable wire frames covered by a cloth sleeve). Timely intervention is critical, because the mortality rate for elective procedures is approximately 5%, whereas the rate for emergency surgery after rupture is roughly 50%.
A point worthy of emphasis is that because atherosclerosis is a systemic disease, a patient with AAA also is very likely to have atherosclerosis in other vascular beds and is at a significantly increased risk for ischemic heart disease and stroke.
Thoracic aortic aneurysms most commonly are associated with hypertension, bicuspid aortic valves, and Marfan syndrome. Less commonly, disorders caused by mutations in the TGF-β signaling pathway are causative. These aneurysms manifest with the following signs and symptoms:
Respiratory or feeding difficulties due to airway or esophageal compression, respectively, because of encroachment on mediastinal structures
Persistent cough from irritation of the recurrent laryngeal nerves
Pain caused by erosion of bone (i.e., ribs and vertebral bodies)
Cardiac disease due to valvular insufficiency or narrowing of the coronary ostia; heart failure induced by aortic valvular incompetence
Aortic dissection occurs when blood splays apart the laminar planes of the media to form a blood-filled channel within the aortic wall (
Fig. 10.20 ). This development can be catastrophic if the dissecting blood ruptures through the adventitia and escapes into adjacent spaces.
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Fig. 10.20 Aorticdissection.(A)Anopenedaortawithaproximaldissectionoriginatingfromasmall,obliqueintimaltear(identified by the probe) associatedwithanintramuralhematoma.Notethattheintimaltearoccurredinaregionlargelyfreeofatheroscleroticplaque.Thedistaledgeoftheintramuralhematoma(black arrows) liesattheedgeofalargeareaofatherosclerosis(white arrow), whicharrestedthepropagationofthedissection.(B)Histologicpreparationshowingthedissectionandintramuralhematoma(asterisk). Aorticelasticlayersareblack, andbloodisred inthissection,stainedwithMovatstain.
Aortic dissection need not be associated with aortic dilation, and the older term dissecting aneurysm should be avoided. Aortic dissection occurs mainly in two age groups: (1) men 40 to 60 years of age with antecedent hypertension (more than 90% of cases); and (2) younger patients with connective tissue abnormalities that affect the aorta (e.g., Marfan syndrome). Dissections also can be iatrogenic (e.g., complicating arterial cannulation during diagnostic catheterization or cardiopulmonary bypass).
Rarely, pregnancy is associated with aortic (or other vessel) dissection (roughly 10 to 20 cases per 1 million births). This typically occurs during or after the third trimester, and may be related to hormone-induced vascular remodeling and the hemodynamic stresses of the perinatal period. Dissection is unusual in the presence of substantial atherosclerosis or other causes of medial scarring, presumably because the medial fibrosis inhibits propagation of the dissecting hematoma (see
Fig. 10.20