Penetrating Atherosclerotic Ulcer

Penetrating atherosclerotic ulcer (PAU) was first described in 1986 by Stan-son et al.75 as a localized defect of intima and media caused by atherosclerotic plaque that has ruptured through the intima with subsequent hematoma formation within the media of the aortic wall. Penetrating ulcer with associated intramural hematoma is regarded as a variant of aortic dissection, however, as an entity distinctly different from classic ("open") dissection and also from intramural hematoma due to ruptured vasa vasorum (IMH)20,76-80. Differences are as below:

• As opposed to classic dissection, there is usually no reentry tear in acute penetrating ulcer and the false lumen will be thrombosed rather than perfused20,76.

• The intimal defect in case of PAU is an atherosclerotic ulcer and not a simple intimal tear20.

• As opposed to intramural hematoma due to ruptured vasa vasorum where the intima is thought to be intact, penetrating ulcer (PAU) implies an intimal defect.

On CT, a focal contrast outpouching representing the ulceration with adjacent intramural hematoma is regarded the most specific imaging appearance of PAU20,76-79. The intramural hematoma is most commonly focal and contained by medial fibrosis that is present with extensive intimal atherosclerosis. Less commonly, the intramural hematoma of a PAU extends along a long segment of the aortic wall, both proximal and distal to the ulceration. Unfortunately, there

Figure 5.21. Axial CT images of penetrating atherosclerotic ulcer with acute intramural hematoma in the aortic arch: (a) unenhanced image shows high attenuation intramural hematoma (white arrow); (b) contrast-enhanced image shows focal contrast outpouching of the true lumen, consistent with penetrating ulcer (black arrow).

Figure 5.21. Axial CT images of penetrating atherosclerotic ulcer with acute intramural hematoma in the aortic arch: (a) unenhanced image shows high attenuation intramural hematoma (white arrow); (b) contrast-enhanced image shows focal contrast outpouching of the true lumen, consistent with penetrating ulcer (black arrow).

are only small case series that correlate the CT imaging characteristics of penetrating atherosclerotic ulcer with histopathologic conformation20,76. Kazerooni et al. retrospectively evaluated 16 cases with a CT diagnosis of PAU; surgical verification was available in seven patients76. In all but one case, the ulceration was located in the thoracic aorta. The seven patients with surgical verification had the following CT findings:

• Focal contrast outpouching representing the ulcer (7/7) (Figure 5.21),

• Adjacent intramural hematoma (7/7) (Figure 5.21),

• Displaced intima calcifications (6/7),

• Mediastinal fluid collection (3/7), and

Quint et al.20 reported 49 patients with surgically proven thoracic aortic disease, including six patients with PAU. In this series, only four of six penetrating ulcers had both ulceration and intramural hematoma on CT. In two cases, CT demonstrated only the intramural hematoma but not the ulceration. There was one false positive CT diagnosis of PAU; however, at surgery there was a dissection with thrombosed false lumen and a simple tear in the dissection flap, with no atherosclerotic ulceration.

Unfortunately, there is considerable controversy regarding the definition of penetrating ulcer (PAU), and some authors regard the presence of intramural hematoma as one of several possible complications but not an obligate finding80. For example, atherosclerotic ulcers have been observed to penetrate the aortic wall with subsequent contained or frank aortic rupture but no intramural hematoma: Batt et al. evaluated eight patients with surgically proven PAU of the abdominal aorta80. None of the patients in this series had associated intramural hematoma, but all eight patients had complications, either contained pseudoaneurysm (n = 5) or periaortic hematoma (n = 3). The authors speculated that intramural hematoma might be more frequent in thoracic than in abdominal PAU.

It adds to the confusion that in clinical practice, the term penetrating ulcer is often used as a descriptive term for any observed ulcerlike aortic lesion, even if there are no associated findings like intramural hematoma or pseudoaneurysm and regardless whether patients are symptomatic. Unfortunately, imaging methods including CT do not allow for direct visualization of the intima except in classic dissection.

Furthermore, the only CT evidence that an observed ulcerlike lesion of the aorta has penetrated the intima is the observation of either adjacent intramural hematoma or signs of even deeper penetration—namely, pseudoaneurysm or periaortic fluid. Thus, the CT finding of an ulcerlike lesion of the aorta without adjacent intramural hematoma might be due to irregular intraluminal thrombus, rather than to a true penetrating ulcer.

To evaluate the significance of the CT finding of an "ulcerlike aortic lesion" regardless whether this constitutes true penetrating ulcer or not, Quint et al. retrospectively evaluated the CT scans of 38 patients in whom such a lesion was observed78. At the time of the initial scan, 22 patients presented with acute symptoms, and 16 patients were asymptomatic. The overall number of lesions included in this series was 56, 50 of which were located in the thoracic aorta. Of 49 lesions with available clinical follow-up, 37 remained clinically stable; 6 of these showed progression on CT. Two lesions were associated with recurrent chest/back pain but were stable on follow up CT. Eight lesions were treated surgically because the patients were either symptomatic or because an aneurysm had developed at the site of the ulcer. Two lesions occurred in patients who died shortly after the initial scan. The only CT feature predictive for clinical outcome on the initial scan was lack of pleural effusion. Presence of intramural hematoma on the initial scan was observed in 22 lesions but was not predictive for clinical outcome. Ulcerlike lesions that progressed on follow up imaging developed into fusiform, saccular, or combined aneurysms.

As a conclusion, although the disease concept of penetrating ulcer (PAU) remains controversial, the CT finding of a focal contrast outpouching of the aortic lumen with associated intramural hematoma is regarded as consistent with the diagnosis of PAU and subsequent dissection of blood into the media. For patient management, the diagnosis of PAU makes an important difference compared to the diagnosis of "simple" intramural hematoma without appreciable intimal disruption (IMH) because of different treatment implications:

As opposed to IMH, PAU may be amenable to endovascular repair. Thus, in all patients with acute intramural hematoma, it is important to search for any focal contrast outpouchings of the true lumen and not to miss the penetrating ulcer that would potentially be amenable to endovascular treatment.

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