Current Understandings and Approach to the Management of Aortic Intramural Hematomas

STATE OF THE ART

Current Understandings and Approach to the Management of Aortic Intramural Hematomas Joshua B. Goldberg, MD, Joon Bum Kim, MD,1 and Thoralf M. Sundt, MD Intramural hematoma is the most enigmatic of the 3 lethal entities comprising acute aortic syndrome. Despite being identified almost 100 years ago, there is considerable controversy surrounding the definition, etiology, management, and the very existence of intramural hematoma. The following review outlines these controversies and discusses their effect on management strategies. Semin Thoracic Surg 26:123–131 I 2014 Elsevier Inc. All rights reserved. Keywords: intramural hematoma, acute aortic syndrome, aortic dissection, penetrating aortic ulcer, aortic surgery

INTRODUCTION Acute aortic syndrome (AAS) is a triad of pathologic crises affecting the aorta comprising 3 not so exclusive entities, aortic dissection (AD), penetrating aortic ulcer (PAU), and, the topic of this review, intramural hematoma (IMH). The 3 entities are often grouped together as they are indistinguishable in their initial clinical presentation and have high associated morbidity and mortality and similar treatment strategies. Ever since 1920, when Krukenberg1 noted a “dissection without intimal tear” on an aortic specimen during a postmortem examination, for which he has credit as the first to identify an IMH, there has been considerable controversy over the definition of an IMH, its management, and the even the truth of its very existence. In the following review of IMH, we set the stage for the discussion of these controversies and describe their effect on management practices. IMH DEFINITION IMH is classically defined as a hematoma within the aortic media without open communication with the true lumen of the aorta via intimal violation. By definition, the presence of intimal disruption as the origin of hematoma collection precludes the Division of Cardiac Surgery, Department of Surgery, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts Address reprint requests to Thoralf Sundt, MD, Massachusetts General Hospital, 55 Fruit St, Boston, MA 02114. E-mail: [email protected] 1 AATS Graham Foundation Travelling Fellow.

1043-0679/$-see front matter ª 2014 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1053/j.semtcvs.2014.07.003

diagnosis of IMH and therefore, IMH may be regarded as a disease primarily of the aortic media. By contrast, PAU refers to a condition where an atherosclerotic lesion with ulceration erodes into the internal elastic lamina as first defined by Stanson et al.2 Thus, PAU is primarily a disease of the intima. AD might be regarded as an overlapping condition, with disease of the media requiring intimal injury to manifest. It is important to note, clinically these 3 processes are not static. For instance, IMH or PAU can progress to AD. The identification of IMH and its differentiation from AD and PAU can be quite challenging and has resulted in considerable debate. Of course one cannot prove a negative—just because intimal disruption is not seen on imaging or examination it does not mean that it does not exist. Accordingly, there are some groups who believe all dissections originate from an IMH. Others advocate abolishment of the IMH terminology altogether, as they believe all IMH represent thrombosed dissections.3 In fact Krukenberg’s original definition of IMH implied there is an undiagnosed intimal tear. In a sense, IMH is ultimately a pathologic diagnosis that can only be made with complete examination of the entire aorta. The association between IMH and PAU creates more confusion and controversy. If one adheres to a strict definition of IMH, the often-used term “PAU with IMH” is an oxymoron as the PAU represents an intimal defect. A more accurate descriptor is PAU with medial thrombosis. Similarly, IMH is often described in association with “ulcerlike projections” (ULP), which are defined as blood-filled protrusions 123

CURRENT UNDERSTANDINGS AND APPROACH TO THE MANAGEMENT OF AORTIC IMHS from the true lumen extending into the thrombosed media.4 Classically described IMH associated with PAU or ULP have been shown to have a poorer prognosis.5 Thus, it is imperative to distinguish between these diagnoses clinically as well as in the literature, especially with some centers advocating for medical management of IMH. With that said, much of the IMH literature consists of varied IMH definitions including PAU with IMH and IMH with ULP (Fig. 1). PATHOPHYSIOLOGY OF IMH In part, the definition of IMH is derived from conflicting theories of its pathogenesis. The oldest and most cited hypothesis to explain the pathophysiological mechanism of IMH is “rupture of vasa vasorum” with intramural bleeding.6 However, there is little direct clinical or experimental evi-

dence to support this concept. Although analysis of surgical and postmortem aortic specimens demonstrates media degeneration and elastin fragmentation similar to AD specimens, the location of an IMH within the media is quite different from AD. The distinguishing feature of IMH is the exterior location within the media near the adventitia, whereas AD extends into the media in closer proximity to the intima.7 Finally, it has been suggested that pathologic changes in the media, such as elastin, ultimately leads to a structural failure of the aortic wall in which the outer part of the aortic media experiences disproportionately high tension and strain. This increased strain could make this outer region of the aorta especially susceptible to failure and expansion during increased loading conditions.8,9 Animal models have shown decreased aortic elasticity and

Figure 1. Ultralow contrast dose CTA for acute aortic syndrome (penetrating aortic ulcer). (A) ECG-gated noncontrast CT image of a patient with acute tearing left back or scapular pain and a history of severe anaphylactoid reaction to iodinated contrast agent demonstrates focal calcification (arrow) of the descending aorta at a site immediately distal to the left subclavian artery. Neither were other calcifications detected, nor was there evidence for intramural hematoma. (B and C) Corresponding sagittal (B) and axial (C) arterial phase images demonstrate the presence of focal atherosclerotic plaque and a tiny intimal disruption at the same site. (D) Oblique coronal image centered on the plaque demonstrates ulcerated disruption of the intimal layer (arrow) with focal eccentric thickening of the aortic wall. Although the aorta is still “ascending” cranially in the thorax, the location beyond the left subclavian artery (“LSc”) indicates the anatomical descending thoracic aorta. The examination was performed after prophylactic premedication to prevent recurrent anaphylactoid reaction, using a minimal dose of 20 mL of contrast agent, given that anaphylactoid reaction has a dose-dependent relationship. CTA, CT angiography; ECG, electrocardiograph. (Color version of figure is available online at http://www.semthorcardiovascsurg.com.)

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CURRENT UNDERSTANDINGS AND APPROACH TO THE MANAGEMENT OF AORTIC IMHS increased wall strain when the vasa vasorum of the aorta is compromised.10,11 Nevertheless, the exact pathophysiological mechanism of IMH still remains unclear. In this context, there is mounting evidence that the vast majority of IMHs are thrombosed AD, as recent studies make use of more sensitive imaging modalities and have identified intimal defects in many of the IMH cases.3 Recent studies suggest that intimal tears are identified in many of the IMH cases.12-14 For instance, Uchida et al3 recently demonstrated that 39 of 50 patients (78%) showed actual intimal tears, with 50% confirmed intraoperatively and 28% detected on computed tomography (CT) scans. In another study by Kitai et al, 38 patients with acute IMH were evaluated using multidetector CT to detect potential intimal defects within the IMH. The study revealed that 71% of patients were recognized as having small intimal defects, particularly in the type B IMH.14 These studies indicate many IMHs actually result from an intimal tear similar to AD rather than bleeding from the vasa vasorum. The study results also suggest, as the sensitivity of imaging improves that the detection rate of very small intimal tears will continue to increase. Herein, lies a controversy of the definition of IMH. Many IMHs may not be a “hematoma in the aortic wall without intimal tear” but may originate from a tear too small to be detected by current imaging technology. If this was to prove to be the case, true IMH will be much less frequent than we observe from the literature. Although it is still impossible to detect tiny intimal defects in every case of AD even using the best available modern imaging modalities, the diagnosis of IMH should remain a “radiologic diagnosis” in real clinical practice if not confirmed by surgical inspection or autopsy. EPIDEMIOLOGY Study of AAS is difficult because it is an uncommon event occurring in 1-3 per 100,000 personyears with high variability in the proportion of AAS comprising IMH.15 A real mystery of IMH is the apparent geographic differences in the proportion of IMH that comprise AAS. For instance, studies from Western countries report its proportion up to 10%,6,16-18 whereas Korean and Japanese groups report much higher rates generally ranging from 20%-40%.19-22 Ethnic or geographic differences have been suggested to explain this discrepancy in the rates between Western and Eastern groups. Alternatively, it may also be attributable to different evaluation practices and treatment algorithms, as well as the lack of uniform definition on the IMH.

Furthermore, possible publication bias is also an important factor to consider because most of the reports on IMH from Japan and Korea are mainly made by a select few centers in each country rather than being derived by analyses based on an overall nationwide database. Interestingly, recent studies from Korea and China report that the proportion of IMH to be roughly consistent with the incidence in the West at 10.7% and 4.7% respectively, which cast some doubt on the geographic and ethnic variability of IMH.23,24

IMAGING OF IMH Imaging is the cornerstone of diagnosis. By far, the most common diagnostic modality by which IMH is made is via CT scan as it is expeditious and has a negative predictive value for diagnosing IMH of approximately 100%.25 In this day and age, CT is readily available, and interpretation is less operator dependent. Furthermore, CT is also the most commonly used modality to rule out other causes of chest pathologies, such as pulmonary embolism. Typical findings on CT suggestive of IMH include a crescentshape area of uniform hyperattenuation (60-70 HU), with associated aortic wall thickening (typically 47 mm) (Fig. 2). One must be careful not to confuse aortic wall thickening noted on imaging with inflammatory processes that may affect the aorta. Magnetic resonance imaging (MRI), with sensitivity for IMH of approximately 100%, is less commonly used because of slower scan times and relative lack of availability in comparison with CT. Nevertheless, MRI provides extraordinary detail of aortic pathology. MRI has the unique ability to differentiate acute vs chronic hematomas. On T2weighted images (blood appears white), acute IMHs (o7 days old) are hyperintense (bright white), whereas chronic IMHs (47 days) are less intense. By contrast, T1-weighted images (blood appears black) of acute IMH are isointense (black) (Fig. 3). In chronic IMH, as the hematoma evolves and degenerates, T1-weighted images become hyperintense (bright). Transthoracic echocardiography is another excellent imaging modality with greater than 90% sensitivity and specificity for IMH.26,27 Disadvantages of transthoracic echocardiography are the inability of imaging the entire aorta, it is highly operator dependent, not readily available and has relative difficulty imaging heavily calcified and atherosclerotic aortas. Historically, aortography has been used in AAS to diagnose AD. Its use to detect IMH is minimal given the lack of intimal disruption.

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Figure 2. CT image of type B intramural hematoma. (A) Axial noncontrast CT scan demonstrates crescentic high-density material along the wall of the descending thoracic aorta consistent with an intramural hematoma (yellow arrows). Stationary, concentrated hemoglobin lead to relatively higher CT density than moving blood, which in subtle cases can be more apparent on noncontrast images. (B and C) Arterial (B) and 2-minute delayed (B) phase axial CT images at the same position as (A) confirm the presence of an intramural hematoma that does not enhance. (D) Oblique sagittal “candy-cane” view (8-mm thick, average intensity projection) demonstrates the z-axis extent of the hematoma (arrows), which is confined to the descending thoracic aorta. (Color version of figure is available online at http://www.semthorcardiovascsurg.com.)

PRESENTATION AND NATURAL HISTORY OF IMH Patients with IMH tend to be older and are more likely to present with aneurysms when compared with those with AD.7,28 Furthermore, IMH is distinctly uncommon in the setting of Marfan syndrome.28 Differences in demographics as well as specific comorbidities among those with IMH and those with AD support the notion that IMH and AD are distinct entities and is not merely a thrombosed AD. In the case of type A disease, patients with IMH are more likely to have pericardial effusions or cardiac tamponade (21% vs 9%, P ¼ 0.004) when compared with those with AD.20,28 The latter findings are consistent with a relatively outer location of the disease in the aortic wall with IMH compared with those of AD. NATURAL HISTORY The natural history of IMH ranges anywhere from complete resolution to rapid progression to dissection or rupture to late aneurysm formation or

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late dissection of rupture.28,20 The location in the aorta influences the behavior and management of IMH, which may be due to different hemodynamic stresses or different material properties as the ascending and the descending aorta have separate embryologic origins. Thus, the remainder of the discussion separates IMH by Stanford classification. TYPE A IMH MANAGEMENT AND OUTCOMES Similar to AD, the traditional management of type A IMH has been emergent surgery owing to relatively high incidence of catastrophic complications in combination with relatively low operative mortality (o10%). Table 1 summarizes the outcomes reported in recent studies of acute type A IMH. There is substantial literature to suggest that type A IMH is a worse actor than type A AD. Tittle et al29 reported a high incidence of early rupture in type A IMH (26% vs 8% of type A AD) combined with a high incidence of progression to AD. Furthermore, the International

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Figure 3. MR image of type B intramural hematoma. (A) Double-inversion recovery, ECG-gated, breath-hold T1-weighted “black blood” image without contrast demonstrates intermediate signal intensity, crescentic thickening displacing the intimal layer of the descending thoracic aorta (yellow arrows). (B) Postcontrast oblique sagittal postcontrast T1-weighted ECG-gated MR image confirms relative hypoenhancement of the intramural hematoma (arrows). Using multiple adjacent images, the z-axis extent of the intramural hematoma (a dissection equivalent) was confined to the descending thoracic aorta (Stanford type B). ECG, electrocardiograph. (Color version of figure is available online at http://www.semthorcardiovascsurg.com.)

Registry of Aortic Dissection data, among others, report higher incidence of pathologic extension beyond the adventitia such as pericardial effusion, tamponade, rupture, and sudden death.18,20,29,30 Overall in-hospital mortality rates vary by series but are generally equivalent to if not less than AD.18,20 Patients who survive to hospital discharge, however, do rather well with an equivalent 1-year mortality as AD (5.3% vs 8.7%, P 4 0.99).18 Traditionally, outcomes of medically managed type A IMH have been poor with 27%-96% of patients receiving initial medical therapy for IMH eventually experiencing adverse aortic events or requiring aortic replacement surgery during follow-up.29 Nevertheless, there has been an argument to treat type A IMH medically. Controversy arose when Song et al published a report in support of medical management of type A IMH. In their practice, medical management was the treatment of choice for 84% of those who presented with symptomatic type A IMH.31 In-hospital mortality of type A IMH was significantly lower than type A AD (7.9% vs 17.2%) with equivalent mortality rates of those who were surgically managed (7.9% vs 10.7%). Furthermore, initial medical management for type A

IMH showed similar in-hospital mortality compared with surgical therapy (7.1% vs 12.5%). However, up to one-third of the medically managed patients experience IMH progression to AD, rupture, or aneurysmal degeneration and ultimately have needed surgery.31-33 Other Asian centers have reported similar medical management strategies.34-36 It is important to note that Song et al excluded IMH with PAU or ULP, which have been shown to be a population with worse outcomes. Criticisms of this approach are the need for a prolonged length of intensive care unit and overall hospital stay as well as frequent CT scans for a disease process with a high conversion rate to surgery in both the short and long term. Useful discoveries of the series studying medical management of type A IMH are factors that predict progression of the type A IMH (Table 2). Although data are derived from relatively small series, the most important factors shown to predict IMH progression are aortic diameter and aortic wall thickness.21,22,37,38 It is unclear if these geographic differences in outcomes and management strategy derive from different pathology or different patient selection or practice patterns. Undoubtedly, there is a subset of patients with type A IMH who can be successfully

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CURRENT UNDERSTANDINGS AND APPROACH TO THE MANAGEMENT OF AORTIC IMHS Table 1. Studies Comparing Medical and Surgical Management in Acute Type A Intramural Hematoma IMH/AAS

No. of Surgical Conversion Patients or Aortic Event

Song et al37

101/357 (28.3%)

Med 85

Kitai et al21

66/298 (22.1%)

Motoyoshi et al35

Surg 16 Med 50

Surg 16 36/80 (45.0%) Med 26

Estrera et al33

36/251 (14.3%)

Harris et al*18

64/1808 (3.5%)

Surg 10 Med 29 Surg 7 Med 10

Hata et al36

171/388 (44.1%)

Late Survival

Event-Free Survival

58.3%-94.2% (3 y)† – –

Early

Late

17 (20.0%) – 16 (32.0%) – 4 (15.4%) – 28 (96.6%) – –

8 (9.4%)

6 (7.1%)

83.1% at 3 y

– 4 (8.0%)

2 (12.5%) 2 (4.0%)

– 3 (11.5%) – 2 (6.9%)

1 (6.0%) 0

Equivalent 94.3% At 5y Equivalent –

1 (10.0%) –

– –

– –

1 (14.3%) 4 (40.0%)

– –

– –

13 (24.1%) 8 (32.0%)

– –

– –

2 (22.2%) 17 (25.8%)

– 68.7% At 10 y 64.9% At 10 y

– 46.8% At 10 y

Surg 9 Med 66

– 10 (40.0%) – 5 (7.6%)

Surg 105

–

Surg 54 34/90 (37.8%) Med 25

Ho38

30-d Mortality

– 2 (20.0%) – 0 – 20 (30.3%) –

4 (3.8%)

– 59.1% (5 y)

–

Med, initial medical therapy; Surg, initial surgical therapy. *Not based on initial intention to treat (surgical conversion rate was not identified). †Rates differ according to the presence of risk factors. Aortic event ¼ rupture, progression to dissection or dilation. Event-free survival ¼ aortic event or surgical conversion or both.

managed without surgery. The important question to be asked is to what extremes one is willing to go to in terms of serial monitoring, prolonged hospitalization, and risk of late death to avoid acute surgery. Furthermore, the increased length of stay undoubtedly required to safely follow patients with ascending aortic pathology puts a resource strain on overextended medical centers. Until further research can elucidate the management outcomes between surgical and medical management strategies in reasonably sized cohort with appropriate randomization or statistical adjustment, optimal management options with individualized approaches are yet to be determined.

TYPE B IMH MANAGEMENT AND OUTCOMES Overall, type B IMH has more favorable short- and long-term outcomes in comparison with type A IMH and type B AD. Mortality is lower in type B IMH (0%4%) compared with type A IMH (7%-27%), which is likely attributable to fewer cardiac complications.28,31 The morbidity and mortality advantage observed in type B IMH compared with AD is infrequent visceral malperfusion.28 Similar to type A IMH, type B IMH tend to have more extramural complications than type B AD such as periaortic hematomas and rupture.28 Reports of long-term survival are quite favorable with 5-year survival as high as 85%.39

Table 2. Risk Factors of Adverse Aortic Events (Aortic Dissection, Conversion to Surgery, and Death) in Medically Treated Type A IMH Kitai et al (n ¼ 50) Song et al37 (n ¼ 85) Hata et al36 (n ¼ 66) Ho et al38 (n ¼ 25)* 21

Aortic Diameter

IMH Thickness

Other Variables

Z50 mm Z55 mm NS P ¼ 0.003†

Z10 mm* Z16 mm Z10 mm* NS

NS Syncope Female* Age, tamponade, low BP, and low level of Hb

BP, blood pressure; Hb, hemoglobin; NS, not significant. All variables showed have P o 0.05. * Results from univariable analyses only. †Cutoff value was not suggested.

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CURRENT UNDERSTANDINGS AND APPROACH TO THE MANAGEMENT OF AORTIC IMHS Table 3. Predictors of Type B IMH Progression to Dissection, Rupture, Surgery, or Death Study (No. of Type B IMH)

Diameter (mm)

Wall Thickness Demographic Other (mm)

Sueyoshi et al39 (37) Kaji et al40 (53) Timperley et al41 (14) Lee et al30 (107)

440*

410*

–

–

442 442

412 –

470* –

ULP* –

449*

48*

466

ULP*

*Identified by multivariable analysis significant predictors of progression. All other values are univariable predictors. All values statistically significant P r 0.05.

The controversy surrounding the appropriate management of type A IMH is not present for type B IMH as there is broad international acceptance of medical therapy because of its relatively low failure rate. For instance, in a study of type B IMH, Kaji et al40 observed only 2 of 53 (4%) patients needing surgery—one for impending rupture at 6 days, the other for aneurysmal degeneration at 65 days. Similarly, the International Registry of Aortic Dissection reported 5% of the type B needing surgical intervention.28 These favorable outcomes do not mean type B IMH is a benign condition. Reports of the rate to progression to AD are variable both in frequency and in time interval.30,39-41 Between 20 days and 36 months after diagnosis, Sueyoshi et al39 described 11% (4/35) progressing from IMH to AD, 2 of which were type A dissections. Progression from a descending IMH to an AD is not uncommon among published series.41 Kaji et al reported only 4% developed AD in follow-up, all of which were localized to the IMH and did not require additional intervention. It is important to mention, focal descending thoracic ADs may not result in alterations of management strategy other than possibly more frequent follow-up and imaging.31 Another variably occurring, yet dire complication of type B IMH is rupture. Reported rates of rupture in type B IMH range from 4%-38%.29,39,40 Rupture has reported to occur over a broad time period ranging from presentation to months after index presentation. Although the variability of reports are undoubtedly affected by the small sample size, most published series and registries report the occurrence of early and late rupture in “stable” medically managed patients, which should be of concern to practitioners who care for these patients in both the acute and chronic phase, as aortic disease can silently progress. Various factors have been shown to predict progression of type B IMH (Table 3). As with type

A IMH, aortic diameter and thickness have been consistent predictors of progression to rupture, dissection, or dilation.29,30,39,40 Sueyoshi et al39 reported a diameter of 440 mm (P ¼ 0.001 with a hazard score of 30) and aortic wall thickness of 10 mm (P ¼ 0.009 with a hazard score of 9) were significant predictors of IMH progression. Kaji reported that age 470 years, ulcerlike plaques in the aorta, wall thickness 412 mm, and diameter 442 mm were predictors. On the contrary, there is a significant portion of type B IMHs that resolve with medical therapy. Kaji et al40 reported 36 of 53 (68%) type B IMHs regressed, 26 of which had complete resolution. Furthermore, multi-institution, South Korean data reported that 78% of their medically managed type B IMHs completely resolved.31 With multiple studies describing a rather indolent course for most type B IMHs, the traditional treatment paradigm has been medical management with close follow-up, including serially imaging. However, there are a proportion of the patients who in follow-up die or need emergent surgery for progression of their aortic pathology. Therefore, attention has been turned to thoracic endovascular aortic repair (TEVAR). With the rapid adoption of endovascular stent graft repair of the descending thoracic aorta pathology, its application to IMH is not clear. Although efficacy has been demonstrated in symptomatic type B dissection and PAU, there are very little data exploring TEVAR use with IMH without PAU.42-46 Intuitively, TEVAR use for AD and PAU makes sense as an endograft is excluding an intimal defect and can thrombose a false lumen. However, in the case with IMH, neither is there an intimal defect to exclude nor is there a false lumen to be thrombosed by the radial pressure of the endograft. Furthermore, as discussed previously, there is evidence that material properties of an IMH aorta are different with more exterior pathology and potential adventitial weakness. Thus, an IMH aorta may neither be able to well tolerate the balloon dilation needed to place the endograft nor be able to well tolerate the radial force of the endograft as the aorta remodels.47,46 With the low complication rate of medical management, the liberal use of stent grafting is unwarranted. Although TEVAR may avoid a major incision, it has its own set of complications, such as iatrogenic dissection or rupture, paralysis, and need for reintervention for endoleaks.45,48 However, there may be a role in properly selected patients such as those who are not surgical candidates or have features associated with risk of complications.

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CURRENT UNDERSTANDINGS AND APPROACH TO THE MANAGEMENT OF AORTIC IMHS CONCLUSION There are numerous controversies in the classification, pathophysiology, and management of IMH. Nevertheless, with our current level of data and understanding it appears as though IMH is a distinct pathophysiological entity affecting the aorta. Although there has been a suggestion of geographic or ethnic differences in the incidence of IMH, recent data suggest these differences may not be as profound as people originally presumed. Despite some centers reporting favorable outcomes from medical management of type A IMH, practitioners should tread with extreme caution when choosing a path of medical management as a relatively high proportion ultimately need surgery. The subset of patients who are more likely to benefit from medical management

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have yet to be clearly described. Caution should also be used when applying TEVAR to type B IMH owing to subtle yet significant pathologic differences in the aorta with IMH compared with the other AAS entities. In summary, IMH remains a lethal and malignant condition of the aorta. From presentation to late follow-up, patients are at risk for catastrophic complications. Practitioners need to remain ever vigilant when caring for these patients. ACKNOWLEDGMENTS We thank Dr Brian Ghoshhajra, MD (Director of Cardiac Imaging, Department of Radiology, Massachusetts General Hospital), for his valuable assistance and guidance in providing the images that appear in the article.

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