Pathologic variants of thoracic aortic dissections: Penetrating atherosclerotic ulcers and intramural hematomas

Abstract

This article confirms the existence of two variants of acute aortic pathology, the penetrating atherosclerotic ulcer (PAU) and the intramural hematoma (IMH), which are radiologically distinct from classic aortic dissection. Table 4 reviews the characteristics distinguishing PAU from classic aortic dissection and IMH. We took as a matter of definition that classic aortic dissection involves a flap which traverses the aortic lumen. We defined PAU and IMH as nonflap lesions, with PAU demonstrating a crater extending from the aortic lumen into the space surrounding the aortic lumen. This categorization can be summarized with the expression, 'no flap, no dissection.' With these definitions made, re-review of the imaging studies for the present report identified 36 such lesions out of 214 cases originally read as aortic dissection. Therefore, these variant lesions accounted for over 1 out of 8 acute aortic pathologies. Besides confirming the existence of the conditions, PAU and IMH, as distinct radiographic lesions, this series strongly suggests that these two conditions constitute distinct clinical entities as well. Table 4 summarizes the clinical patterns of these two entities as apparent from the present study, and contrasts them with classic aortic dissections. In particular, the following observations, some of which are consonant findings in smaller series, can be made regarding the typical patient profiles of PAU and IMH from the present study: The patients with PAU and IMH are distinctly older than those with type A aortic dissection (74.0 and 73.9 versus 56.5 years, P = 0.0001). Although not statistically significant, PAU and IMH patients tend to be older than patients with type B aortic dissections as well. For PAU and IMH, unlike aortic dissection, the concentration in the elderly is manifested in a very small standard deviation of the mean age (see Fig. 13); these two entities, PAU and IMH, are essentially diseases of the seventh, eighth, and ninth decades of life. Patients with PAU and IMH are almost invariably hypertensive (about 94% of cases). The pain of PAU and IMH mimics that of classic aortic dissection, with anterior symptoms in the ascending aortic lesions and intrascapular or back pain with descending aortic lesions. Unlike classic dissection, PAU and IMH do not produce branch vessel compromise or occlusion and do not result in ischemic manifestations in the extremities or visceral organs. PAU and IMH are more focal lesions than classic aortic dissection, which frequently propagates for much or the entire extent of the thoracoabdominal aorta. PAU is uniformly associated with severe aortic arteriosclerosis and calcification, whereas classic dissection often occurs in aortas with minimal arteriosclerosis and calcification. PAU and IMH tend to occur in even larger aortas than classic aortic dissection (6.2 and 5.5 versus 5.2 cm, P = 0.01). PAU and IMH are strongly associated with AAA, which is seen concomitantly in 42.1% of PAU patients and 29.4% of IMH patients. PAU and IMH are largely diseases of the descending aorta (90% for PAU and 71% for IMH). Although our pathology data is limited, we do feel that an inherent difference in the histologic intramural level of the hematoma may underlie the pathophysiologic process that determines which patient develops a typical dissection and which develops an intramural hematoma. In particular, we feel that the level of blood collection is more superficial, closer to the adventitia, in IMH than in typical aortic dissection. This may explain why the inner layer does not prolapse into the aorta on imaging studies or when the aorta is opened in the operating room. This more superficial location would also explain the high rupture rates as compared to classic aortic dissection (Fig. 14, Table 3). We did find PAU and IMH to behave much more malignantly than typical descending aortic dissection. As seen in Figure 6, the rupture rate is much higher than for aortic dissection. Documented rupture occurred in 35.3% of IMH patients and in 42.1% of PAU patients. All but one PAU or IMH present in the ascending aorta ruptured. These ruptures all occurred during the initial hospitalization. These rupture rates are much higher than the 7.5% seen for ascending dissection and the 4.1% seen for descending dissection (P = 0.0001). (Of course, we do not ordinarily observe ascending dissections without surgery long enough to allow them to manifest their known poor prognosis). Therefore, PAU and IMH are extremely malignant in their early behavior. For this reason, it is essential to differentiate PAU and IMH from typical aortic dissection. Once patients with PAU and IMH survive the initial hospitalization, they do well, without late symptom recurrence or rupture in follow-up (mean 28 months in our study). What therapeutic correlates can we draw from this experience? First, detection is important. IMH and PAU are life-threatening conditions, which may not be detected on presentation unless the clinician is aware of the distinguishing radiologic features. These are enumerated in the previous paragraphs. Second, the following suggestions are made regarding management: We recommend early operative intervention for all PAU and IMH affecting the ascending aorta. Ascending lesions, although uncommon, in our experience uniformly ruptured or progressed and were often lethal. Therefore, these patients may be treated as those with classic ascending aortic dissections. This posture is supported by other series. Patients with PAU and IMH lesions in the descending aorta can be observed initially and treated with 'antiimpulse' therapy, including β-blockade and afterload reduction. These lesions are more serious than classic descending aortic dissection, and a low threshold for surgical intervention must be maintained. If radiographic findings are ominous (severely bulging hematoma, extensive subadventitial spread, extra-adventitial blood, bloody pleural effusion, or deeply penetrating ulcer), surgery should be performed preemptively. In the absence of ominous initial radiographic findings, repeat imaging should be carried out within 3 to 5 days. In case of any progression, in volume or extent of the hematoma or overall size of the aorta, surgery should be performed preemptively to prevent rupture. Likewise, if symptoms are not controlled or recur on medical treatment, surgery should be performed. This posture is supported by most other series. If patients tolerate early medical management without clinical deterioration, our experience suggests that they may continue to be followed conservatively. In long-term follow-up, general size criteria for surgical intervention on the thoracic aorta can be applied. Kouchoukos and Dougenis recently reviewed strategies for evaluation and treatment of aortic pathologies. Our findings and clinical recommendations are consonant with those reported in smaller series of variant aortic pathologies examined in that review. As IMH and PAU primarily affect older individuals with significant comorbidity, however, our above recommendations must be tempered by consideration of the patient's overall condition and general outlook. Some of these patients may not be appropriate candidates for the aggressive surgical strategy outlined. We are just beginning to understand the identity and behavior of these lesions, and our management suggestions are provisional recommendations regarding the treatment of penetrating ulcer and intramural hematoma. Continued experience will be required to assess more completely the natural history of these variants of aortic dissection and to achieve more definitive treatment recommendations. Furthermore, although we have described these variant lesions as entities distinct from aortic dissection, it is likely that intermediate lesions exist, and that ulcer, hematoma, and dissection lie on a continuum of disease processes.