Chapter30 Aorta

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Section V: Cardiac Radiology

LAD

RBCA

LCCA

LM

T

LSCA

RCA

F

F

F T

A

B

C

D

Figure 30.31.  Type A Aortic Dissection, RCA Occlusion, and Propagation Into the Right Brachiocephalic Artery. Axial maximum intensity pro- jection (MIP) CT image at the level of the left main coronary artery ( A ) demonstrates the proximal margin of the dissection flap ( arrow ) extending to the aortic root. The left main ( LM ) and left anterior descending ( LAD ) coronary arteries are patent. The dissection extends into the descending thoracic aorta with delineation of the flap ( arrow ), true ( T ), and false ( L ) lumens. Oblique coronal MIP image at the level of the right coronary artery ( B ) demonstrates the dissection flap ( black arrow ) extending into the ostium of the right coronary artery ( RCA ) leading to its occlusion ( white arrows ). Axial image at the level of the aortic arch ( C ) demonstrates the dissection flap ( arrow ), true ( T ), and false ( F ) lumens. Note inward displacement of intimal calcifications ( arrowhead ). Axial image at the level of the arch vessels ( D ) demonstrates propagation of the dissection flap into the right brachiocephalic artery ( RBCA, white arrow ). The left common carotid ( LCCA ) and subclavian ( LSCA ) arteries are supplied by the true lumen.

bolus tracking. With a test bolus, a small amount of contrast is administered and repeat axial images are obtained at a single level to assess the time to maximum opacification. Once this is determined, the full contrast bolus is administered, and imag- ing occurs with a scan delay as indicated by the timing bolus. With bolus tracking, a region of interest (ROI) is prescribed in the ascending aorta, the contrast bolus is administered, and when the Hounsfield Units in the ROI exceed a preset thresh- old, the scan is triggered. If there is concern for an ascending aortic dissection, prospective ECG gating should be employed to avoid false-positive diagnoses from motion or other artifacts at the aortic root. With gating and careful angiographic tim- ing, the coronary arteries may also be evaluated for dissection propagation in this setting.

Aortic Dissection Thoracic dissections are classified according to the Stanford sys- tem by their most proximal extent: type A dissections involve the ascending aorta (proximal to the innominate artery) and require immediate surgical management with stent–graft place- ment (Figs. 30.31 and 30.32). Type B dissections involve only the descending aorta (distal to the leftsubclavian artery) and are often managed medically unless there is evidence of end-organ ischemia or impending rupture, in which case surgical or endovascular stent grafting is indicated (Figs. 30.33 and 30.34). Dissections that involve the aortic arch but do not extend prox- imal to the innominate artery (Figs. 30.35 and 30.36) are rare,

T

T

F

F

A

B

Figure 30.32.  Type A Aortic Dissection With Occlusion of the Right Common Carotid Artery. Parasagittal CT reformat ( A ) demonstrates a type A dissection with very slow flow in the false lumen ( F ) compared to the true lumen ( T ). The dissection flap extends into and occludes the right common carotid artery ( white arrow ). Axial image from a head CT ( B ) shows relative hypoattenuation of nearly the entire right cerebral hemisphere ( white arrows ) due to right common carotid artery occlusion.