Ann Thorac Surg 2005;79:1518-1521
© 2005 The Society of Thoracic Surgeons
Original articles: Cardiovascular
Pathologic Characteristics and Surgical Indications of Superacute Type A Intramural Hematoma
Keiji Uchida, MDa,*,
Kiyotaka Imoto, MD, PhDa,
Masato Takahashi, MD, PhDb,
Shin-ichi Suzuki, MD, PhDa,
Susumu Isoda, MD, PhDa,
Mitsugi Sugiyama, MD, PhDc,
Jiro Kondo, MD, PhDa,
Yoshinori Takanashi, MD, PhDa
a Cardiovascular Center, Yokohama City University Medical Center, Yokohama, Japan
b Department of Pathology, Yokohama City University Medical Center, Yokohama, Japan
c Critical Care and Emergency Medical Center, Yokohama City University Medical Center, Yokohama, Japan
Accepted for publication November 10, 2004.
* Address reprint requests to Dr Uchida, Cardiovascular Center, Yokohama City Medical Center, 4-57 Urafune-cho, Minami-ku, Yokohama, 232-0024, Japan (E-mail: uchida{at}urahp.yokohama-cu.ac.jp).
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Abstract
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BACKGROUND: The treatment policy for acute intramural hematoma involving the ascending aorta remains controversial.
METHODS: This study compared the pathologic characteristics of intramural hematoma with those of acute aortic dissection with a false lumen. The study group comprised 69 patients with intramural hematoma and 156 with acute aortic dissection who underwent emergency operation between 1995 and 2003.
RESULTS: Patients were significantly older in the intramural hematoma group than in the dissection group (67.7 ± 7.2 years compared with 59.8 ± 11.6 years; p < 0.0001). Pericardial hemorrhage was present in a higher proportion of patients in the intramural hematoma group than in the dissection group (66.7% compared with 50.6%; p = 0.0257). Three patients (4.3%) died in the intramural hematoma group, whereas 26 patients (16.7%) died in the dissection group (p = 0.011). Histopathologic examination showed no difference in the severity of medial changes, but the site of dissection differed. The thickness of the residual media of the adventitia side was 0.21 ± 0.12 mm in the intramural hematoma group compared with 0.32 ± 0.22 mm in the acute aortic dissection group. Dissection was significantly nearer the adventitia in the intramural hematoma group (p = 0.0016).
CONCLUSIONS: Dissection is nearer the adventitia in intramural hematoma than in dissection, leading to a greater probability of rupture. These results suggest that operation as soon as possible after the onset of intramural hematoma will contribute to improved survival.
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Introduction
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Intramural hematoma (IMH) shares many clinical characteristics with acute aortic dissection (AAD), but the treatment policy for IMH involving the ascending aorta remains controversial. Emergency operation is performed on patients with complications such as cardiac tamponade, but many centers instead recommend close surveillance and medical therapy to dissolve hematoma in the dissection. However, many patients die of rupture or require an operation because of dissection with a false lumen.
Few reports have been published on "superacute" IMH of the ascending aorta within 24 hours after symptom onset. Various aspects of the pathogenesis and prognosis of this condition remain unclear. We operated on patients with superacute IMH or AAD and analyzed the clinical, surgical, and histopathologic characteristics of these conditions. Based on our findings, we propose guidelines for the treatment of IMH and AAD.
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Patients and Methods
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We defined IMH by computed tomography as thickened aortic wall caused by intramural hemorrhage, with crescentic or circular areas along the aortic wall that fail to appear on contrast enhanced computed tomographic scans, signifying noncommunication with the aortic true lumen. Earlier reports defined IMH that has no intimal tear, but because we cannot recognize the existence or absence of IMH in acute phase without complete aortography or autopsy, we excluded this definition.
We studied 69 patients with IMH involving the ascending aorta and 156 patients with type A AAD who were brought to our center and underwent emergency operation between 1995 and 2003. These two groups were compared with respect to preoperative factors, surgical findings, and surgical outcome. Typical computed tomographic scans obtained from patients with IMH or AAD are shown in Figure 1.
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Fig 1. Classic computed tomographic findings. (AAD = acute aortic dissection [right]; IMH = intramural hematoma [left].)
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The severity of medial degeneration and necrosis of the aortic wall and the depth of the dissection were examined histopathologically. Specimens were obtained from the central region of the resected ascending aorta, fixed in formalin, and prepared for histopathologic examination. Aortic specimens obtained surgically from 44 patients with IMH and 112 patients with AAD were examined histopathologically. The severity of medial changes was classified as mild, moderate, or severe (Table 1). The site of the dissection in the media was expressed as the thickness of the residual media of the adventitia side (Figs 2 and 3).
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Fig 2. Histopathologic findings of aortic wall in intramural hematoma. The site of the dissection in the media was expressed as the thickness of the residual media of the adventitia side. (Elastica-van Gieson stain, x40 before reduction.)
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Fig 3. Histopathologic findings of aortic wall in acute aortic dissection. The site of the dissection in the media was expressed as the thickness of the residual media of the adventitia side. (Hematoxylin and eosin stain, x40 before reduction.)
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Statistical analysis was carried out using Student's t test, the Mann-Whitney test, and the 
2 test. Statistical significance was indicated by p < 0.05.
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Results
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Preoperative characteristics of the groups are provided in Table 2. No difference was noted in sex, but the patients with IMH were significantly older. Twenty-six patients (37.7%) with IMH were admitted within 3 hours after symptom onset, and 53 (76.8%) were admitted within 6 hours. In AAD group, 64 patients (41.0%) were admitted within 3 hours after symptom onset, and 111 (71.2%) were admitted within 6 hours. At admission, 14 patients (20.3%) with IMH and 27 (17.3%) with AAD had shock with a systolic blood pressure of 90 mm Hg or less, a difference that was not significant.
In the IMH group, the mean time from admission to the start of the operation was 118 ± 57 minutes, 46 patients (66.7%) had pericardial hemorrhage at operation, and 34 (49.3%) had cardiac tamponade. The incidences of pericardial hemorrhage and cardiac tamponade were significantly higher than those in the AAD group. In the IMH group, the entry was in the ascending aorta in 19 patients and in the arch in 10 patients. No entry in the ascending aorta and the arch was significantly more frequent in the IMH group than in the AAD group (58.0% compared with 25.0%; p < 0.0001) (Table 3).
Surgical Outcomes
Of the 69 patients with IMH, 51 received ascending aortic replacement, 17 ascending partial arch replacement, and 1 total arch replacement; 2 patients also had coronary artery bypass. Among the 156 patients with AAD, 93 underwent ascending aortic replacement, 30 partial arch replacement, and 33 total arch replacement; 9 patients additionally received aortic root replacement and 9 coronary artery bypass. Three operative deaths (4.3%) occurred in the IMH group, compared with 26 deaths (16.7%) in the AAD group (Table 4). The major cause of death was disturbed organ blood flow. The surgical outcome was significantly better in the IMH group.
Histopathologic Findings
The severity of medial degeneration or necrosis in the IMH group was mild in 22 patients, moderate in 24, and severe in 1 (Table 5). For the AAD group the severity was mild in 42 patients, moderate in 57, and severe in 8. These differences were not significant.
The site of dissection differed between the two groups. The thickness of the residual media of the adventitia side was 0.21 ± 0.12 mm in the IMH group compared with 0.32 ± 0.22 mm in the AAD group (Table 6). Dissection was significantly nearer the adventitia in the IMH group (p = 0.0016).
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Comment
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Emergency operation after the onset of symptoms is an established policy for the treatment of AAD involving the ascending aorta, and outcome has recently improved markedly. Intramural hematoma is considered a subtype or precursor of AAD, and its treatment policy and indications for the operation remain a matter of debate [1–3]. Some patients with IMH may respond to conservative therapy with resolution of hematoma or shrinkage or disappearance of the false lumen, even when the ascending aorta is involved. Previous reports have therefore recommended that patients without cardiac tamponade receive antihypertensive conservative therapy and be closely followed up by imaging studies; surgery is performed on the onset of complications [4–7].
Several case reports have documented rupture or transition to AAD during follow-up of patients with IMH [8–11]. Some surgeons caution that the risk of rupture during the acute stage of IMH is similar to that associated with AAD, although many patients who have reached the chronic phase of IMH have a good prognosis [12, 13]. A recent study has shown that surgical therapy has a better outcome than conservative therapy with respect to early and midterm results [14], and an increasing number of studies recommend prompt surgical treatment [15, 16].
Our experience with many patients in the acute phase of AAD or IMH who underwent emergency operation indicates that early IMH has a higher rate of pericardial hemorrhage and cardiac tamponade than early AAD. Song and colleagues [17] also reported higher incidences of mediastinal hematoma, pericardial effusion, and pleural effusion in patients with IMH than in patients with AAD, but did not discuss potential causes for this difference.
Rupture of the false lumen, a major cause of cardiac tamponade, is related to intraluminal pressure and wall strength. Given that intraluminal pressure in IMH is not higher than that in AAD, we examined histopathologic specimens assuming that wall strength in IMH would be weaker than that in AAD. We found no difference in the severity of medial degeneration, but the site of dissection in IMH was nearer the adventitial side of the media than that in AAD, indicating that the wall of the false lumen was thinner in IMH than in AAD. The progression of dissection closer to the adventitia would most likely discourage reentry and increase the risk of a tear in the adventitia (Fig 4). Coady and associates reported similar findings in 1999 [18], but our study provides histopathologic evidence to support the higher incidence of rupture in IMH than in AAD.
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Fig 4. Schema of development of dissection. (AAD = acute aortic dissection [bottom]; IMH = intramural hematoma [top].)
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Patients with IMH were significantly older than those with AAD. This finding suggests that an intimal tear in the aortic wall led to dissection nearer the adventitial side of the media in elderly patients, resulting in a clinical presentation of IMH rather than AAD.
The time from symptom onset until treatment is an important determinant of the treatment policy for IMH. Patients with organized thrombi and false lumen shrinkage with no rupture after symptom onset usually have a good prognosis in response to conservative therapy. Immediately after onset, however, determining whether "superacute" IMH will resolve or will rupture and evolve to AAD is often difficult. One study has recommended that a maximum aortic diameter of 5 cm should be used as the cutoff point to differentiate between these two conditions [19]. However, a recent study reports that type A IMH has a high risk of rupture, regardless of aortic diameter [20].
Acute IMH has a higher rate of rupture than AAD, and the pathologic basis for this greater risk has been demonstrated. Although some patients may respond to conservative therapy, differentiation of such patients early after symptom onset is difficult. Moreover, operative results for aortic dissection have markedly improved. Few patients die of intraoperative hemorrhage, and most deaths are caused by impaired organ blood flow. Because IMH has a low risk of impaired organ blood flow [18], further improvement in operative outcome is expected. Only 3 of the 69 patients with IMH in our series died. Emergency operation during the "superacute" stage of IMH will most likely improve survival, similar to the outcome in AAD.
Conclusion
We studied the pathologic and operative characteristics, surgical outcome, and histopathologic findings of IMH involving the ascending aorta. Patients with IMH of the ascending aorta tended to be elderly, and many had cardiac tamponade. The outcome of emergency operation was good. As compared with AAD, the dissection in IMH was located nearer the adventitial side of the media of the aortic wall, creating a higher risk of adventitial rupture. Our results suggest that surgery as soon as possible during the "superacute" stage of IMH will contribute to improved survival.
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Abstract
Introduction
