The patient gave her consent by telephone to present the information contained in this Echo Rounds.
A 59-year-old woman with chest and back pain and electrocardiographic evidence of ischemia was admitted to an outside hospital and initially treated with anticoagulation. A widened mediastinum was revealed by chest radiograph, and a subsequent computed tomography scan diagnosed a type A aortic dissection with large pericardial effusion. The patient later developed cardiogenic shock, was tracheally intubated and supported with vasoactive medications. She was emergently transferred to our institution's intensive care unit, while hypotensive and with severe metabolic acidosis. She was emergently brought to the operating room.
Evaluation of the patient by a focused transesophageal echocardiographic examination (TEE) revealed a large pericardial effusion with evidence of systolic right atrial collapse, consistent with tamponade physiology. Two-dimensional and color-flow Doppler imaging of the entire aorta revealed the following: (i) no intimal tear or dissection flap, (ii) ascending aorta with thickened posterior wall distal to the sinotubular junction (see Supplemental Digital Content 1 and 2: Video 1, http://links.lww.com/AA/A332, and Video 2, http://links.lww.com/AA/A333), (iii) aortic arch lumen 3.0 cm in diameter with a 0.7-cm intramural thickening (Fig. 1A), and (iv) descending aorta lumen 3.1 cm in diameter, with a crescent-shaped echodense area containing areas of echolucency and measuring 1.7 cm in thickness (Fig. 1B) (see Supplemental Digital Content 3: Video 3, http://links.lww.com/AA/A334). Doppler color-flow examination did not reveal flow inside the echolucent areas of the thickened aortic wall segments. The above TEE findings were consistent with the diagnosis of intramural hematoma (IMH). The aortic valve was not affected by the IMH. Likewise, the absence of regional wall motion abnormalities and normal ventricular sizes suggested that the coronary arteries were also spared.
Upon entering the chest, the pericardial effusion was slowly drained to facilitate strict arterial blood pressure control. The patient underwent cannulation of the femoral artery and right atrium, and an uneventful replacement of the ascending aorta and arch was performed under circulatory arrest lasting 26 minutes (cardiopulmonary bypass time: 132 minutes). Postoperatively, the patient experienced transient leg weakness, which resolved eventually.
Acute aortic syndromes—comprising IMH, aortic dissection, and penetrating atherosclerotic ulcers—are accompanied by a high rate of mortality and morbidity.1 All of these conditions, when located in the ascending aorta, require immediate attention and surgical intervention. Partial aortic transection or total disruption of the aorta secondary to trauma are also included in the differential diagnosis of acute aortic syndromes.
Acute IMH is a hematoma of the aortic wall without an intimal flap or intimal tear on imaging (Fig. 2). IMH is considered to be a precursor of impending aortic dissection. The principal causes of IMH are rupture of the vasa vasorum or, less often, an atherosclerotic ulcer.1 IMH may also be due to an iatrogenic trauma. Percutaneous interventions involving insertion of guidewires or catheters in the aorta may cause microtears in the intima, which may eventually progress to IMH.2 This etiology of IMH is usually undetectable by echocardiography but may be confirmed at surgery by direct visualization of a small intimal tear without a decompressing exit tear.2 IMH differs from aortic dissection, where an intimal flap separates 2 distinct aortic lumens. Although bleeding into the aortic wall is present in both aortic dissection and IMH, a false lumen is not present in IMH. As was the case in this patient, expansion of the wall hematoma impinges on the aortic lumen and may not result in increased aortic diameter.1 Some have advocated a wall thickness criterion as small as 5 mm to diagnose IMH, whereas normal aortic wall thickness is <3 mm.2
When an acute aortic syndrome is suspected, a complete evaluation of the entire aorta should be performed. Starting from the midesophagus, the ascending aorta should be viewed in the short and long axes. Next, the probe should be turned to the left and advanced until the distal descending thoracic aorta is imaged. Optimally, the depth of the sector image should be decreased to 4 to 5 cm, and transducer frequency increased, to maximize resolution of this near-field structure. By slowly withdrawing the probe, the descending aorta can be scanned from the distal thoracic region until the arch is encountered. The distal arch is then examined in the long and short axes. The distal ascending aorta and proximal aortic arch cannot be seen by TEE secondary to the interposition of the air-filled trachea, which impedes conduction of ultrasound. If the proximal aorta is compromised, one must further investigate the competency of the aortic valve and ventricular wall motion to detect signs of aortic insufficiency or coronary involvement, respectively.
Caution should be taken to differentiate an atherosclerotic lesion from IMH.3 A frequent echocardiographic feature of IMH is the presence of echolucent spaces within the aortic wall, as seen in Videos 1 through 3 (see Supplemental Digital Content 1 through 3, Video 1, http://links.lww.com/AA/A332, Video 2, http://links.lww.com/AA/A333, and Video 3, http://links.lww.com/AA/A334). These are noncommunicating, blood-filled cavities, which may progress toward rupture or simply reabsorb.1 Another major diagnostic challenge is differentiating between IMH and aortic dissection when the false lumen is thrombosed. In IMH there is a smooth intimal surface of homogeneous consistency, as opposed to aortic dissection, in which the intimal surface is usually irregular with or without calcifications and the thrombosed false lumen is heterogeneous in density (Table).3 However variable the echocardiographic characteristics of traumatic aortic injuries may be, a hematoma of the media is mostly found in IMH.4,5
A review of >1010 patients in the International Registry of Aortic Dissection demonstrated that only 5.7% of nontraumatic acute aortic syndromes met the criteria of IMH.6 A small number of these patients (16%) developed aortic dissection.6 IMH is associated with comorbidities similar to aortic dissection, such as myocardial ischemia, acute renal failure, spinal cord ischemia, pleural and pericardial effusions, and tamponade.6 The clinical presentation of our patient was made far more dramatic because of the large pericardial effusion and tamponade physiology. Pericardial effusions are present in about 65% of patients and are the result of the intense inflammatory response to the aortic hemorrhage.6
The site of aortic involvement determines the clinical significance and management of IMH. The classification of IMH as type A or type B IMH is similar to that used in aortic dissection: a type A IMH is localized in the ascending aorta, and a type B IMH is contained in the descending aorta.2 Although IMH is noted to resolve in about 10% of patients, the associated mortality warrants urgent surgical intervention when located in the ascending aorta. A less aggressive approach (observation and medical therapy of hypertension) is advocated for IMH located in the descending thoracic aorta or distal aortic arch.6
Midesophageal ascending aorta short-axis view: a thickening of the posterior aortic wall with echolucent spaces is seen. The right pulmonary artery (RPA) is seen at the top of the image sector, and the superior vena cava (SVC) is seen to the right of the ascending aorta (AA). IMH = intramural hematoma.
Midesophageal ascending aorta long-axis view: a thickening of the posterior aortic wall with echolucent spaces is seen in the posterior aorta. The right pulmonary artery (RPA) is seen at the top of the image sector. IMH = intramural hematoma.
Descending aorta (DA) long-axis view: echocardiographic features of an intramural hematoma (IMH) are seen in the anterior aortic wall, which is thickened and contains echolucent spaces.
1. Nienaber CA, Richartz BM, Rehders T, Ince H, Petzsch M. Aortic intramural hematoma: natural history and predictive factors for complications. Heart 2004; 90: 372–4
2. Song JK. Diagnosis of aortic intramural haematoma. Heart 2003; 90: 368–71
3. de Souza DG, Blank RS, Mazzeo FJ, Singh KE. Penetrating ascending aortic athersclerotic ulcer. Anesth Analg 2009; 109: 1035–37
4. Beauchesne LM, Veinot JP, Brais MP, Burwash IG, Chan KL. Acute aortic intimal tear without a mobile flap mimicking an intramural hematoma. J Am Soc Echocardiogr 2003; 16: 285–8
5. Willens HJ, Kessler KM. Transesophageal echocardiography in the diagnosis of diseases in the thoracic aorta. Chest 2000; 117: 233–43
6. Evangelista A, Mukherjee D, Mehta RH, O'Gara PT, Fattori R, Cooper JV, Smith DE, OH JK, Hutchison S, Sechtem U, Isselbacher EM, Nienaber CA, Pape LA, Eagle KA, International Registry of Aortic Dissection Investigators. Acute intramural hematoma of the aorta: a mystery in evolution. Circulation 2005; 111: 1063–70
Clinician's Key Teaching Points By Roman M. Sniecinski, MD, and Martin J. London, MD
- Acute aortic syndromes represent a spectrum of disease ranging from acute intramural hematoma (IMH), to penetrating atherosclerotic ulcer, to the more familiar aortic dissection. IMH consists of a blood collection within the aortic wall, presumably due to rupture of the vaso vasorum. While there is no actual intimal tear, IMH is considered a precursor to a dissection and is treated as a surgical emergency if present in the ascending aorta.
- Just as in aortic dissection, transesophageal echocardiography (TEE) plays a critical role in the diagnosis of IMH. Because there is not a false lumen, a flap will not be seen. Instead, asymmetrical thickening of the media to >5 mm is the key finding. There is an echolucent space within the aortic wall that will often appear gray in consistency because of the clotted blood. This must be distinguished from an atherosclerotic plaque, which arises from the endothelium and protrudes into the lumen of the aorta.
- In this case, the patient presented with typical signs of an aortic dissection: chest and back pain, a widened mediastinum on chest radiograph, and a pericardial effusion. TEE examination, however, did not reveal the classic finding of a dissection flap in the ascending aorta. Fortunately, the authors were able to recognize the intramural thickening of the ascending aorta consistent with IMH, and the patient underwent appropriate surgical intervention.
- Aortic dissection, whose diagnosis is familiar to all intraoperative echocardiographers, actually represents only 1 entity in the spectrum of life-threatening acute aortic syndromes. It is imperative that intraoperative echocardiographers learn to recognize other presentations, such as IMH, so that patients receive the appropriate surgical treatment.