Chapter30 Aorta

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Section V: Cardiac Radiology

aortitis. Giant cell arteritis (GCA), rheumatic fever, and relaps- ing polychondritis may result in ascending aortic aneurysms, while Takayasu arteritis may affect the ascending aorta, aortic arch, arch vessels, abdominal aorta, and/or pulmonary arteries. Infective aortitis may arise in the setting of bacterial endocardi- tis, with resultant aneurysm formation most often in the proxi- mal ascending aorta. Historically, syphilis was a more common cause of ascending aortitis and aneurysm; incidence of syphilitic aortitis has decreased, but a number of other organisms (includ- ing Streptococcus and Staphylococcus spp.) can be implicated in infective aortitis (“mycosis”) which may lead to formation of a “mycotic” aneurysm. Bicuspid valve is an independent risk factor for ascending TAA, unrelated to the presence of associ- ated aortic stenosis. Chest radiography may demonstrate dilation of the ascend- ing aorta or arch (Fig. 30.25), with or without associated cal- cifications. Technique is also an important consideration; the ascending aortic contour may be exaggerated if the patient is rotated to the right and this should not be confused for an aneurysm. There may be tracheal deviation and/or left upper lobe atelectasis in the setting of an aortic arch aneurysm. CT angiography (CTA) has replaced traditional catheter angi- ography as the mainstay of imaging and has the benefit of extraluminal evaluation, though treatment cannot be con- currently performed as with catheter angiography. CTA will demonstrate typically fusiform and concentric focal dilation of the ascending aorta or arch (Fig. 30.29) to greater than 4 cm. Patients with Marfan syndrome may demonstrate dilation of the main pulmonary artery in addition to annu- loaortic ectasia (Fig. 30.30). Aneurysms cause turbulent flow patterns with nonlaminar flow, often eventually resulting in discontinuous or circumferential mural thrombus formation (Fig. 30.25). Noncontrast imaging is not always routinely per- formed in follow-up imaging of known aneurysms, but some studies have suggested that focal crescentic hyperattenuation in mural thrombus may be a sign of impending rupture. Mul- tiplanar (MPR) and three-dimensional reformats can be eas- ily rendered, allowing for accurate orthogonal measurements and aiding with pre- and/or periprocedural planning and

Ascending Thoracic Aorta and Aortic Arch Aneurysms

Thoracic aortic aneurysms (TAAs), defined as aortic enlarge- ment to greater than 4 cm with preservation of vessel wall integrity—that is, without intimal disruption—may occur anywhere along the vessel; 50% occur in the ascending aorta (proximal to the right brachiocephalic artery), 10% in the aor- tic arch, and 40% in the descending aorta (distal to the left subclavian artery). There are a multitude of risk factors for the development of TAA, but by far the highest association is with atherosclerosis, which is seen in 70% of cases. Aneurysms sec- ondary to atherosclerotic disease are more commonly seen in the descending thoracic aorta but may occur anywhere along the thoracic and abdominal aorta (Fig. 30.28). Thus, imag- ing of the abdominal aorta is also indicated in these patients. Homocystinuria, Marfan syndrome, and other connective tissue disorders may result in dilation of the aortic annulus and prox- imal ascending aorta, termed annuloaortic ectasia. Ascending aortic aneurysm can also result from noninfective or infective

Figure 30.28.  Multifocal Thoracoabdominal Aortic Aneurysm. Sag- ittal CT image in a 69-year-old woman demonstrates multifocal aneu- rysms in the thoracic ( black arrows ) and infrarenal abdominal aorta ( white arrow ). Note layering mural thrombus in the abdominal aortic aneurysm.

Figure 30.29.  Ascending Thoracic Aortic Aneurysm. Axial CT in a 77-year-old woman demonstrates marked dilation of the ascending aorta measuring 7.7 cm consistent with aneurysm ( A ).