Streak artefacts of the thoracic aorta: pseudodissection.

Streak artefacts running across images of the aorta can mimic aortic dissection on CT. We have compared 12 patients suffering from dissection with 45 others. Some artefacts were found in every patient. Such misleading appearances were more obtrusive in dissectors. However, we have found several pointers that help distinguish true intimal flaps from artefacts. Flaps are usually thin structures showing mild curvature. Artefacts are generally linear and vary in thickness. Their orientation may change markedly from one CT section to the next; they frequently extend beyond the confines of the aorta. In the ascending aorta, artefacts usually run at an angle of approximately 66 degrees to the coronal plane; especial care should be taken before diagnosing a straight intimal flap in that orientation. Careful study of images on the monitor rather than on film is a further help in the important distinction between artefact and intimal flap.