Imaging in the diagnosis of acute aortic dissection: Report on time-benefit and risk-benefit

Acute aortic dissection is a dramatic event in which the outcome is strongly influenced by the time necessary for the diagnosis. Surgically untreated type A aortic dissection has a mortality rate ranging from 60% within the first hours to 90% within 3 months; type B, medically treated dissection, has a survival rate of 80% within the first year. For both types a rapid diagnosis is of extreme importance in experience and the technologic advances of each hospital. Standard chest X-ray can be useful especially if it shows an enlargement of the mediastinum, which guides to the second step in diagnostic testing which is, depending on the setting, echocardiography or computed tomography, and rarely angiography. Standard echocardiography has a very low sensitivity and a moderate specificity. Transesophageal echocardiography can give information about: intimal flap entry (color flow Doppler), extension of the dissection (up to the supradiaphragmatic level), distinction between true and false lumen, left ventricular function and presence of aortic regurgitation. Computed tomography is more accurate in detecting the total extension of the side branch involvement. Aortic angiography, still widely requested by the majority of cardiovascular surgeons, represents a higher risk procedure although giving important information similar to those already mentioned. Magnetic resonance imaging offers the best imaging by multiplane approach but cannot be performed in critically ill patients. In terms of risk-benefit and time-benefit the best diagnostic sequence in the unstable patient should consist in: chest X-ray, transesophageal echocardiography acid/or computed tomography scan. Aortic angiography may be avoided and the surgeon must become familiar to all new imaging techniques.