Chapter30 Aorta

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Section V: Cardiac Radiology

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Figure 30.35.  Type B Dissection With Aortic Arch Involvement. Axial CT images at the level of the lower ( A ) and mid-aortic arch ( B ) demon- strate a dissection flap ( arrows ) that extends to the proximal aspect of the arch but does not propagate beyond the origin of the right brachioce- phalic artery and thus does not meet the definition of a type A dissection; dissections involving the arch have been incompletely characterized in the medical and surgical literature.

aorta may be complicated by severe aortic regurgitation, car- diac tamponade due to hemopericardium, and/or coronary artery occlusion depending on propagation (Fig. 30.31). Rup- ture into the right ventricle, left atrium, venae cavae, and pul- monary arteries is also possible, leading to large left-to-right shunts. Elsewhere, end-organ hypoperfusion/ischemia may result from propagation of the dissection flap into the arch or abdominal vessels (Fig. 30.32). Chest radiographs (Fig. 30.37) are often the initial study but may be normal in up to 40% of cases. The frontal view may demonstrate tracheal deviation, mediastinal widening, loss of the aortic knob contour, enlargement of the ascending and/or descending aorta, pericardial effusion, or inward dis- placement of intimal calcifications which may be apparent if prior radiographs are available for comparison. CTA should be performed in the setting of positive findings on chest radiographs or high clinical suspicion and is critical

for diagnosis and treatment planning. On noncontrast imaging, there may be inward displacement of intimal calcifications. On angiographic phase imaging, the classic intimomedial flap is seen in the vast majority of cases. The true and false lumens can usually be distinguished by the relatively increased contrast enhancement and smaller size of the true lumen in relation to the false lumen, due to the increased pressures in the false lumen (Figs. 30.31 to 30.34). This increased pressure also causes the corners of the true lumen to demonstrate an acute angle with the intimal flap, which can help differentiate between the two. However, a later timing of the angiogram and/or fenestrations in the flap may confound these findings. In extremely rare cases, there may be circumferential intimal disruption (“shearing”) with concentric true/false lumens. CTA is also useful to evaluate propagation of the dissection flap into branch vessels (Fig. 30.32). MRI and MRA can be performed using abbreviated pro- tocols with rapid, single breath-hold sequences with similar

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Figure 30.36.  Type B Dissection With Aortic Arch Involvement. Axial balanced steady state free precession (bSSFP) gradient echo ( A , C ) and double inversion recovery (DIR) T2-weighted ( B ) MR images demonstrate the intimomedial dissection flap ( arrows ) with delineation of the true ( T ) and false ( L ) lumens. The true lumen ( T ) is smaller and demonstrates acute angles with the dissection flap, while the larger false lumen ( F ) demonstrates obtuse angles at interface with the flap. Note also the small pericardial and left pleural effusions, most evident in A . Sagittal refor- mat ( C ) shows the dissection extending into the arch but not involving the ascending aorta.