Page 491 - Hall et al (2015) Principles of Critical Care-McGraw-Hill

CHAPTER 42: Aortic Dissection 361

However, it is now rarely used due to development of advanced non-
invasive techniques with the added benefit of improved detection of the
aortic IMH and penetrating ulcer variants. 33-37
Since type A dissections are life-threatening surgical emergencies, it is
critical to assess involvement of the ascending aorta.
Contrast-enhanced CT scanning is readily available at most institu-
tions and is the most commonly used modality to evaluate aortic dis-
sections, particularly in patients with type B. Specific identification
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of true and false lumens with a flap is possible, as well as detection of
pericardial effusion and accurate depiction of the extent of the dissec-
tion. The newer spiral (helical) CT scans that are now available in most
hospitals yield excellent two- and three-dimensional images and should
be electrocardiographically gated to reduce motion artifacts from a
pulsating aorta (Fig. 42-9A and B). CT scanning is very accurate for
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the diagnosis of dissection (̴98-100% accuracy) 32,33,40 and is superior
FIGURE 42-8. A. Aortogram (lateral projection). Grossly dilated ascending aorta (open arrow) to transesophageal echocardiography (TEE) for the detection of aortic
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with visible intimal flap (solid arrow). Note normal descending aorta. B. Contrast-enhanced CT scan of branch involvement (̴96% accuracy). Unlike TEE, however, CT does
the thorax of the same patient. Arrow identifies intimal flap. (Reproduced with permission from Kotler N, not yield information regarding aortic insufficiency or left ventricular
Steiner RM. Cardiac Imaging: New Technologies and Clinical Applications. Philadelphia, PA: FA Davis; 1986.) function and requires exposure to potentially nephrotoxic radiographic
contrast and radiation and may be problematic in unstable patients.
Transthoracic echocardiography (TTE) has low sensitivity to diag-
Several imaging techniques including aortography, computed tomo- nose aortic dissections due to limited visualization of the distal ascend-
graphic (CT) scanning, magnetic resonance imaging (MRI), and echo- ing aorta, aortic arch, and descending aorta. A dissection flap can
cardiography are highly accurate for the diagnosis and classification of be occasionally seen in the ascending aorta that yields the diagnosis
dissections. In the past, aortic angiography was commonly used as the initial (Fig. 42-10). 36,41 Application of harmonic imaging and administration
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definitive diagnostic method with high sensitivity and specificity (Fig. 42-8). of contrast may improve the accuracy of TTE in diagnosis of ascending

FIGURE 42-9. Contrast-enhanced spiral CT with 3D reconstruction shows extensive type A aortic dissection involving the ascending aorta, the arch and descending aorta down to the iliac
arteries (A) and involvement of the right coronary artery (B).

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