Chapter30 Aorta

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Chapter 30: Thoracic Aorta

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Figure 30.37.  Type A Thoracic Aortic Dissection. Frontal ( A ) and lateral ( B ) chest radiographs in a 36-year-old man demonstrate a widened, lobulated mediastinal contour (between arrowheads ).

sensitivity/specificity to CTA, with similar visualization of the intimomedial flap, true, and false lumens (Fig. 30.36). MR is also particularly useful in root dissections, where retrograde flow dephasing across the aortic valve on steady state free precession (SSFP) sequences is diagnostic of aortic regurgi- tation. As mentioned above, proximal aortic dissections may rupture into the pericardium, resulting in hemopericardium; in patients with possible tamponade, functional cinematic car- diac MR imaging with SSFP allows evaluation for gross visual inspection of wall motion through the cardiac cycle. Further, end-systolic and end-diastolic volumes can be quantified using postprocessing software to calculate stroke volumes and car- diac output. However, in most instances, patients with ascend- ing dissections are unstable and require immediate surgical intervention.

Intramural Hematoma IMH describes acute hemorrhage within the aortic wall and represents 5% to 15% of cases of AAS. IMH was tradition- ally thought to represent a distinct disease process that resulted from rupture of the vasa vasorum within the media, forming a hematoma without communication to the aortic lumen. TEE, however, provides the best images of the intima, and the com- mon finding of intimal irregularity in cases of IMH suggests that an intimal “microtear” may be the inciting event, a theory corroborated by the fact that such tears are often found at the time of surgery and/or in pathologic analysis of IMH specimens. On CT, IMH is characterized by continuous, often cres- centic, hyperdense thickening of the aortic wall seen on noncontrast imaging (Fig. 30.38); there may also be inward

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Figure 30.38.  Type B Progressing to Type A Intramural Hematoma (IMH). Axial nonenhanced ( A ) and contrast-enhanced ( B ) CT images at the level of the right pulmonary artery in a 73-year-old woman demonstrate crescentic high attenuation intramural hematoma involving the descending thoracic aorta ( white arrows ), best seen on the non-contrast portion of the examination. The IMH extended to the level of the left subclavian artery but did not extend into the arch or ascending aorta. Motion artifact in the ascending aorta on the contrast portion of this non-gated study ( yellow arrow , B ), which is absent on the non-contrast portion ( yellow arrow , A ) should not be confused with an intimal flap or IMH. Axial nonenhanced ( C ) and contrast-enhanced ( D ) images at the level of the left pulmonary artery taken 4 days later demonstrate interval increase in IMH along the descending aorta ( arrows ), with new hyperattenuating crescentic thickening along the ascending aorta ( arrowheads ), consistent with progression to type A IMH.