Diagnosis of thoracic aortic dissection. Magnetic resonance imaging versus transesophageal echocardiography.

Abstract

BACKGROUND Aortic dissection requires prompt and reliable diagnosis to reduce the high mortality. The purpose of this study was to assess the reliability of both ECG-triggered magnetic resonance imaging (MRI) and transesophageal two-dimensional echocardiography combined with color-coded Doppler flow imaging (TEE) for the diagnosis of thoracic aortic dissection and associated epiphenomena. METHODS AND RESULTS Fifty-three consecutive patients with clinically suspected aortic dissection were subjected to a dual noninvasive imaging protocol in random order; imaging results were compared and validated against the independent morphological "gold standard" of intraoperative findings (n = 27), necropsy (n = 7), and/or contrast angiography (n = 53). No serious side effects were encountered with either imaging method. In contrast to a precursory screening transthoracic echogram, the sensitivities of both MRI and TEE were 100% for detecting a dissection of the thoracic aorta irrespective of its location. The specificity of TEE, however, was lower than the specificity of MRI for a dissection (TEE, 68.2% versus MRI, 100%; p less than 0.005), which resulted mainly from false-positive TEE findings confined to the ascending segment of the aorta (TEE, 78.8% versus MRI, 100%; p less than 0.01). In addition, MRI proved to be more sensitive than TEE in detecting the formation of thrombus in the false lumen of both the aortic arch (p less than 0.01) and the descending segment of the aorta (p less than 0.05). There were no discrepancies between the two imaging techniques in detecting the site of entry to a dissection, aortic regurgitation, or pericardial effusion. CONCLUSIONS Both MRI and TEE are atraumatic, safe, and highly sensitive methods to identify and classify acute and subacute dissections of the entire thoracic aorta. TEE, however, is associated with lower specificity for lesions in the ascending aorta. These results may still favor TEE as a semi-invasive diagnostic procedure after a precursory screening transthoracic echogram in suspected aortic dissection, but they establish MRI as an excellent method to avoid false-positive findings. Anatomic mapping by MRI may emerge as the most comprehensive approach and morphological standard to guide surgical interventions.

Intimal Tear Without Hematoma

“…The importance of this is that physicians who first see patients with classic symptoms of aortic dissection should be aware that current imaging techniques may not fully exclude the presence of subtle forms of aortic dissection despite reports of 97% to 100% sensitivity for detecting classic (class 1) aortic dissection. 11,[13][14][15] It should be noted that one third of patients with aortic dissection are not diagnosed as having aortic dissection before death. 19 At least 3 of our patients would probably have died shortly from cardiac tamponade or rupture if they had not undergone surgery.…”

“…1,5,24 TEE is usually considered the gold standard for detection of aortic dissection with a reported sensitivity of 97% to 100%. [11][12][13][14][15] The aortic dissection may not be detected, however, if there is not extensive separation of the intimal layer resulting in a flap or septum or if there is only a slightly thickened wall with hematoma and clot occluding the tear site. 7 MRI is reported to have a 98% to 100% sensitivity but suffers the same shortcomings.…”

“…7 MRI is reported to have a 98% to 100% sensitivity but suffers the same shortcomings. 1,3,5,[13][14][15][16] Nonetheless, MRI is considered more accurate in detecting intramural blood or blood clot in the class 2 intramural hematoma type of dissection. CT scanning with contrast is reported to have an 83% to 94% sensitivity for detection of aortic dissection 1,5,11,13 ; however, an intimal tear is very rarely visualized on CT scan.…”

Effect of medical and surgical therapy on aortic dissection evaluated by transesophageal echocardiography. Implications for prognosis and therapy. The European Cooperative Study Group on Echocardiography.

“…Computed tomography and magnetic resonance imaging can be used to obtain this additional information. 43,49 Intravascular ultrasound also appears to be a promising new technique that may overcome current limitations.50 The information not obtained for these reasons would not have influenced the conclusion of this study insofar as the other parts of the aorta are very well imaged, allowing the detection of entry tears, thrombus formation, intimal flaps, and flow in the true and false lumens.…”

Dissection of the aorta

“…Transoesophageal echocardiography has a sensitivity of 98% and a specificity of 100%, but there may be a hypertensive response to probe introduction so this should only be performed in centres with expertise. [2][3][4] In unstable patients in whom type A dissection is clinically obvious transoesophageal echocardiography may confirm the diagnosis and clearly delineate the site and extent of the dissection process at anaesthetic induction for surgical repair.…”