Problems and pitfalls in the evaluation of thoracic aortic dissection by computed tomography.

Several conditions can lead to either false positive or false negative diagnoses of aortic dissection by computed tomography (CT) with intravenous administration of contrast medium. Insufficient contrast enhancement may cause intimal flaps to be missed, leading to a false negative diagnosis. False positive diagnoses result when extraaortic structures (e.g., mediastinal veins, pericardium, thickened pleura, and lung) are mistaken for false channels in the aorta. Superimposition of structures in thick CT slices may cause intimal calcifications to appear displaced. Streak artifacts across the descending aorta can resemble double aortic channels or intimal flaps. Fusiform aneurysms with thrombus are often hard to distinguish from thrombosed dissections by CT as well as by aortography.