Three techniques have been touted recently for evaluation of aortic dissection: contrast-enhanced computed tomography (CT), MRI, and transesophageal echocardiography. Aortography, though, probably remains the âœgold standard.â All of these imaging methods have advantages and disadvantages, and all have claimed superiority.
CT scan is probably the easiest test to do in the acute situation and is readily available and reliable (90% accuracy). True and false lumens can usually be readily demonstrated, as can the intimal flap in the ascending aorta if it is involved. Imaging before, during, and after contrast administration increases sensitivity.
The multiplanar imaging capability of MRI makes it an ideal method to image the aorta. Dissections are especially well demonstrated if the false lumen is partially clotted or if there is a dramatic difference in rate of blood flow between true and false lumens. However, because of pulsatile motion in the aorta, a thin intimal flap may be missed. MRI is also nearly impossible to perform in the critically ill patient.
Transesophageal echocardiography has been claimed to be quite sensitive for type B (descending) aortic dissection, but it is operator-dependent. A multiplane, or omniplate, scope is now available which visualizes the ascending aorta with accuracy.
Aortography images only contrast flowing in a lumen. If the false lumen is clotted, dissection may be only indirectly diagnosed by aortography as narrowing of the lumen of the aorta or thickening of the wall. Aortography is useful, however, in evaluating the origins of the great vessels in type A aortic dissection, as well as in evaluating associated aortic regurgitation.