Chapter30 Aorta

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Chapter 30: Thoracic Aorta

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Figure 30.33.  Type B Aortic Dissection With Impending Rupture. Parasagittal image from a CTA ( A ) shows the intimomedial flap ( yellow arrows ) extending to the level of the left subclavian artery ( red arrow ) but not involving the vessel or extending proximally into the aortic arch, consistent with a type B dissection. The true lumen ( T ) is smaller in size and shows increased contrast opacification compared to the false lumen due to the increased pressures within the false lumen. Axial image ( B ) shows the large size of the false lumen ( F ) compared to the true lumen ( T ). The maximum diameter of the aorta was 7.1 cm. Although most type B dissections are treated medically, this patient was treated surgically due to the large size of the aorta and the risk of subsequent aortic rupture.

and bicuspid aortic valve, cocaine and methamphetamine use, pregnancy, and aortitis. The altered microenvironment and function of the media predispose to the acute phase of dissec- tion when the intima is disrupted, with resultant blood flow from the true aortic lumen into the media and formation of a second, false lumen. The intimomedial tear most commonly occurs along the right lateral wall of the ascending aorta, 1 to 2 cm from the sinotubular junction, or in the proximal descend- ing aorta near the insertion of the ligamentum arteriosum, the sites of maximum shear stress. Once blood has entered the false lumen, it propagates longitudinally along the aortic wall, typ- ically in retrograde fashion; a second, reentrance tear allows blood to circulate through the false lumen. This process also induces a robust inflammatory response—the aortic wall is fri- able and fragile in the acute phase, with a higher risk of rapid expansion and/or rupture compared to the chronic setting (Figs. 30.33 and 30.34). Dissections involving the ascending

comprising approximately 7% of all dissections. They are not specifically classified by the traditional surgical systems and have not been entirely characterized in the medical or surgi- cal literature. For the purposes of reporting and to facilitate understanding among providers, they may be described as type B dissections with aortic arch involvement. Postoperative surveillance imaging in patients who undergo endovascular treatment is important to assess for the presence of endoleaks, discussed in more detail later in the chapter. The pathogenesis of aortic dissection is a complex process involving degeneration of the aortic media, a dynamic struc- ture that plays a vital role in regulating aortic compliance among other functions. This degeneration may be congenital, secondary to aberrant or defective protein production (e.g., in Marfan and Ehler–Danlos syndromes), or acquired, most com- monly secondary to chronic hypertension which causes medial degeneration. Other risk factors include Turner syndrome

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Figure 30.34.  Type B Aortic Dissection With Rupture. Axial CT in the angiographic ( A ) window/level demonstrates the intimomedial flap ( arrow ), with delineation of the true ( T ) and false ( F ) lumens. The large area of contrast extravasation extending posteromedially from the pos- terior aspect of the pseudoaneurysm ( arrowheads ) represents rupture. The soft tissue window/level ( B ) shows the mediastinal hematoma (*) to better advantage; the esophagus is obscured. Coronal ( C ) and sagittal ( D ) reformats can be easily rendered from the original dataset at the work- station; the sagittal view demonstrates partial thrombosis of the false lumen ( F ) in the mid-distal descending thoracic aorta.