Penetrating Atherosclerotic Ulcer

Penetrating atherosclerotic ulcer (PAU) is an ulcer that develops within an atherosclerotically diseased portion of the thoracic or rarely the abdominal aorta, penetrating the internal elastic lamina and into the aortic media and associated with a localized intramural hematoma (Fig. 4E) [20]. This most often develops in elderly hypertensive patients with severe atherosclerotic disease and most commonly affects the descending thoracic aorta (90%) [15]. While ulcerated atherosclerotic plaques limited to the aortic intima may be detected as incidental findings on contrast-enhanced thoracic CT, most patients with PAU present with chest and back pain indistinguishable from type B aortic dissection. In most cases the ulcerating lesion is limited in extent by the locally advanced atherosclerotic disease present within the adjacent portion of the aorta, although extension along the length of the aorta or through the media and adventitia with pseudoaneurysm formation can occur. As with IMH, the diagnosis of PAU among patients presenting with acute aortic syn-

Figure 8 Intramural hematoma (IMH) with rapid development of aneurysmal dilatation. (A) Contrast-enhanced scan shows a mildly dilated descending aorta with a mural crescent of high-attenuation material representing an IMH. (B) Repeat CT obtained 48 hr later due to persistent pain shows aneurysmal dilatation of the descending aorta with development of a left pleural effusion. (C) Oblique sagittal maximum intensity projection (MIP) image obtained from the scan in (B) shows fusiform aneurysmal dilatation of the middescending aorta. Left thoracotomy performed emergently showed impending rupture of an aneurysmal descending aorta with a subadventitial hematoma.

Figure 8 Intramural hematoma (IMH) with rapid development of aneurysmal dilatation. (A) Contrast-enhanced scan shows a mildly dilated descending aorta with a mural crescent of high-attenuation material representing an IMH. (B) Repeat CT obtained 48 hr later due to persistent pain shows aneurysmal dilatation of the descending aorta with development of a left pleural effusion. (C) Oblique sagittal maximum intensity projection (MIP) image obtained from the scan in (B) shows fusiform aneurysmal dilatation of the middescending aorta. Left thoracotomy performed emergently showed impending rupture of an aneurysmal descending aorta with a subadventitial hematoma.

dromes was likely underrecognized in the era prior to cross-sectional imaging with CT: In the above-mentioned series from Coady and colleagues at Yale University, 19 (9%) of 214 patients initially diagnosed as aortic dissection were found to have PAU on review of imaging, surgical, and pathologic studies [15].

Contrast-enhanced spiral CT with the use of axial and planar reconstructions is the primary method of diagnosis of PAU. The characteristic finding is a localized ulceration penetrating through the aortic intima within the mid to distal third of the descending aorta (Fig. 9) [21,22]. There may be inward displacement of intimal calcifications, allowing distinction from an ulcerated atherosclerotic plaque limited to the intima (Fig. 4C). Focal thickening of the adjacent aortic wall is seen, representing the associated intramural hematoma. The cephalocaudal extent of the ulceration is most easily appreciated on coronal or sagittal reconstructions. While MR and TEE can depict the ulceration and associated intramural hematoma without the need for intravenous contrast, the lower inherent spatial resolution of these techniques and more widespread access to CT makes contrast-enhanced spiral CT the modality of choice for suspected PAU. Aortography can depict PAU projecting from the aortic lumen if filmed in tangent to the ulcer crater.

Complications of PAU include progression to classic aortic dissection, embolization of material from the ulcer into the distal arterial circulation, extensive intramural hematoma formation, and development of a pseudoaneu-rysm with subsequent rupture (Fig. 10). Branch vessel occlusion does not

Figure 9 Penetrating atherosclerotic ulcer of the aorta. (A) Contrast-enhanced CT shows an ulcer (arrow) projecting anteromedially from the middescending aorta. (B) Oblique sagittal reconstruction shows the ulcer in profile.

Figure 10 Pseudoaneurysm complicating penetrating atherosclerotic ulcer. (A) Contrast-enhanced CT at level of left atrium shows a large collection (c) enhancing simultaneously with the aortic lumen. Note medially-displaced intima with calcifications (curved arrows). (B) Oblique sagittal reconstruction shows a pseudoaneurysm with its neck (straight arrows) seen in profile. The aneurysm and penetrating ulcer were surgically confirmed.

Figure 10 Pseudoaneurysm complicating penetrating atherosclerotic ulcer. (A) Contrast-enhanced CT at level of left atrium shows a large collection (c) enhancing simultaneously with the aortic lumen. Note medially-displaced intima with calcifications (curved arrows). (B) Oblique sagittal reconstruction shows a pseudoaneurysm with its neck (straight arrows) seen in profile. The aneurysm and penetrating ulcer were surgically confirmed.

occur in uncomplicated PAU. Although patients with descending PAUs, particularly those with significant contraindications to surgery, can be managed conservatively, several series have shown a tendency for PAUs to progress to aneurysm formation with an incidence of rupture exceeding 40%. This rate of rupture is significantly higher than that seen in classic aortic dissection or IMH [22,23]. Therefore, nonoperated patients should be followed closely with repeat cross-sectional imaging studies obtained within days of initial presentation to detect complications. Patients that require surgical intervention typically undergo replacement of the diseased aortic segment with an interposition graft [24], a procedure that is more extensive than repair of an intimal flap in aortic dissection and is associated with a higher incidence of paraplegia due to spinal cord ischemia [25].

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