Chapter30 Aorta

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Chapter 30: Thoracic Aorta

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Figure 30.30.  Marfan Syndrome With Aortic and Pulmonary Artery Involvement. Sagittal CT image ( A ) in a 59-year-old man demonstrates aortic annulus/root aneurysm ( A ), with characteristic “tulip” appearance of the dilated root. Axial oblique reformat through the sinuses of Val- salva ( B ) demonstrates aneurysmal dilation measuring 4.8 cm ( A ). Sagittal CT image ( C ) demonstrates aneurysmal dilation of the main pulmo- nary artery ( double-headed arrow ), which is one of the established criteria for the diagnosis of the syndrome.

navigation for interventionalists. These can be particularly helpful over time for risk stratification. MR and MR angiography (MRA), like CT, are also highly sensitive and specific for aneurysm, along with mural throm- bus and other associated complications. Cine sequences allow visualization of flow patterns, though further study is needed to determine the clinical usefulness of this information. MR may be the most appropriate modality in younger patients and/or those requiring more extensive follow-up imaging, given the lack of ionizing radiation; and non–contrast-enhanced imaging is likely adequate in patients with allergies or poor renal function. Ascending aortic aneurysms may be complicated by dis- section or rupture, and rupture is the leading cause of death in these patients. The risk of rupture increases with size, and ascending aortic aneurysms greater than 6 cm carry a risk of rupture of approximately 14%. Rupture carries a 97% to 100% mortality rate, if not emergently treated; the periop- erative mortality associated with repair is not insignificant but is considerably lower in elective compared to emergent repair (9% vs. 22%). For this reason, early diagnosis is cru- cial, and patients with known aneurysms are monitored with regular, serial imaging to evaluate for size and interval growth. Ascending thoracic aneurysm diameter greater than 5.5 cm and/or interval growth (greater than 0.5 cm in 6 months or 1 cm in 1 year) are/is indication(s) for intervention, either sur- gical or endovascular. In the setting of connective tissue dis- ease such as Marfan syndrome, there is a lower threshold for repair, usually greater than 5 cm. Descending Thoracic Aortic Aneurysms Aneurysms in the descending aorta are most commonly asso- ciated with atherosclerosis, though aneurysms secondary to other diseases including collagen vascular disease, infective aortitis, and autoimmune/inflammatory disease may occur in the descending aorta as well. Chest radiography may demonstrate dilation of the descending aortic contour (Fig. 30.25); any associated calci- fications will be displaced outward in a true aneurysm. CTA is highly sensitive and specific for aneurysm, with or without associated mural thrombus. MRA is also highly sensitive and specific for detection of aneurysms and their complications. Though hemodynamically unstable patients are unsuitable

for MR imaging, it may be more appropriate in the setting of routine surveillance imaging, particularly given the lack of ionizing radiation. Descending thoracic aortic aneurysms may be complicated by dissection, rupture, or fistula formation to the esophagus and/or airways; rupture is the leading cause of death. Risk fac- tors for rupture include age, size greater than 5 cm, hyperten- sion, smoking, and COPD. The rate of growth increases with aneurysm size and is estimated at 0.12 cm/yr for aneurysm diameter greater than 5.2 cm. Thus, aneurysms are monitored with serial imaging; size greater than 6.5 cm and/or interval growth (greater than 0.5 cm in 6 months or 1 cm in 1 year) are/is indication(s) for open surgical or endovascular treat- ment. Operative mortality is 5% to 12% with renal failure (5% to 13%) and spinal cord ischemia (4% to 30%, depend- ing on the extent of disease/repair), among the major postop- erative complications. As in the ascending aorta, aneurysms associated with connective tissue disease are managed more aggressively with earlier intervention. Acute Aortic Syndrome Acute aortic syndrome (AAS) includes aortic dissection, acute intramural hematoma (IMH), and PAU, which share the com- mon classical clinical presentation of excruciating chest pain that may radiate to the back. While these have traditionally been classified as distinct entities, mounting evidence suggests that they may rather represent variants or a spectrum of dis- ease, as described in more detail below. The three cannot be distinguished by clinical history or physical examination, and thus, imaging plays an integral role in diagnosis. Transesopha- geal echocardiography (TEE), multidetector CT (MDCT)/CTA, and MRA are all useful, highly sensitive, and specific. Owing to its ubiquity, rapid acquisition, and high accuracy, CTA is the most commonly employed modality in this setting, with a sensitivity and specificity of 100% and 98%, respectively, for thoracic aortic dissection. Careful consideration of imaging parameters and the manner of intravenous administration of contrast material for CTA is paramount. Noncontrast phase imaging is important to identify IMH, and timing of imaging relative to administration of the contrast material bolus is crit- ical for optimal imaging. Two commonly used methods for ensuring arterial phase imaging are the timing/test bolus and