Chapter30 Aorta

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Section V: Cardiac Radiology

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A

Figure 30.39.  Penetrating Atherosclerotic Ulcer (PAU). Axial image from a CTA ( A ) in an 82-year-old man shows a contrast outpouching in the mid-descending thoracic aorta ( white arrow ) which extends beyond the calcified intima ( yellow arrow ), consistent with a PAU. Noncontrast CT image ( B ) just inferior to this level shows subtle high attenuation in the aortic wall ( white arrow ) due to adjacent hematoma. It is important to differentiate PAU from an ulcerated plaque, as the two have different treatments and outcomes.

displacement of atherosclerotic calcifications. On postcon- trast imaging, the hyperdensity is often less apparent and can be overlooked or misdiagnosed. MR likewise demonstrates the crescentic wall thickening, which may demonstrate T1 and T2 signal abnormality depending on the age of the hem- orrhage. Like dissection, IMH is classified by the Stanford system and is divided into type A and type B. Type B IMH is treated medically in most instances. Like those with type A aortic dissection, unstable patients with type A IMH usually undergo emergent surgery. However, there is debate regard- ing the treatment of patients with type A IMH who are clin- ically stable. This is secondary to the variable clinical course of IMH in which the hematoma may regress (10%), rup- ture (20% to 45%), or evolve into a frank aortic dissection (28% to 47%). Unfortunately, the course of a type A IMH is difficult to predict although if an IMH and PAU are seen concomitantly, this generally harbors a higher risk of pro- gression. Given that some cases of type A IMH regress, some studies suggest initial medical therapy with surgery for those that progress to a frank dissection or expansion of the IMH. However, other studies show an increased mortality with this method. For this reason, serial imaging with CT or MR may be of critical importance in patient care, particularly in those with acute type A IMH who are treated medically. Like type A dissections, extension of the hematoma into the mediastinum or pericardium can occur with type A IMH. Penetrating Atherosclerotic Ulcer PAU describes internal erosion into the aortic media and typically manifests on the background of severe atheroscle- rotic disease. This most commonly occurs in the descending aorta, though ulceration may be seen anywhere along the thoracic aorta, with worse prognosis at the aortic root or along the proximal ascending aorta. PAU is thought to rep- resent up to 7.5% of cases of AAS. On contrast-enhanced CT and on MRA with or without contrast, PAU manifests as

a focal erosion into the aortic wall in the setting of typically severe atherosclerosis (Fig. 30.39) and may be distinguished from other causes of AAS by the focal vessel ectasia, absence of a flap, and lack of compression of the lumen from which the PAU arises. In some cases, it may be difficult to distin- guish PAU from a background of complex atherosclerotic disease; however, PAU typically has a crater-like shape which extends beyond the calcified intima of the aorta, while complex ulcerated plaques are often more jagged appearing and do not extend beyond the intima. Progression of PAU is unpredictable but early identification is critical, as the ulcer can erode into the media with associated IMH (Fig. 30.40). When seen together, these findings herald poor prognosis, with further complications in up to 70% of patients, including formation of saccular aneurysms, aortic rupture, and dissection. Rupture appears to be more common than dissection in the setting of PAU. Treatment typically involves stent grafting, particularly in acute or symptomatic cases, with medical management and imaging surveillance reserved for asymptomatic patients or those with chronic, stable disease. Aortic Pseudoaneurysm Aortic pseudoaneurysm is a focal irregular outpouching of the aorta secondary to intimomedial disruption, with extravasa- tion contained by a variable amount of adventitia and by the surrounding mediastinal tissues. Pseudoaneurysms are most typically seen in the setting of traumatic aortic injury (TAI) or in the postoperative setting after cardiac or aortic vascular surgery, but they may also be seen in the setting of particu- larly aggressive/destructive infections and rare cases of rup- tured dissection. Traumatic thoracic pseudoaneurysms are described in more detail later in the chapter, but most typically occur due to rapid deceleration/shearing forces at the sites of maximum traction; the most common such site is along the aortic isthmus, the narrowing between the distal arch and