Acute aortic dissection: typical and atypical imaging features.

Acute aortic dissection (AAD) is the most common emergency affecting the aorta. Noninvasive imaging allows prompt and reliable diagnosis of AAD and has largely supplanted aortography. However, atypical imaging features and diagnostic pitfalls can delay lifesaving therapy. An intimal flap is the characteristic feature of AAD. If there is flow within both lumina, typical imaging features are probably present. If the false lumen is thrombosed or there is no intimal tear to permit flow through the false lumen, a distinct intimal flap may not be present. Secondary signs of AAD include an intramural or periaortic acute thrombus, which manifests as a high-attenuation cuff or crescent on unenhanced computed tomographic scans. Other conditions that can reduce the conspicuity of the intimal flap include atypical configurations of the flap, such as seen with short dissections or with multiple false channels, in which case the flaps are complex. Finally, aortic anomalies may cause confusion.