HELICAL CT FOR THE DIAGNOSIS OF EXTRACRANIAL INTERNAL CAROTID-ARTERY DISSECTION

Background and Purpose We attempted to evaluate the sensitivity of hel ical CT for the diagnosis of extracranial internal carotid artery (ICA ) dissection. Methods Sixteen consecutive patients with 18 angiographi cally confirmed extracranial ICA dissections were studied with a helic al CT protocol with large-volume acquisition and thin axial slice reco nstructions. A control group including normal and atherosclerotic ICAs was formed for comparison, and a blind interpretation of CT images wa s made by two observers. We evaluated the presence of stenosis, eccent ric lumen, mural thickening, aneurysm, occlusion, and annular contrast enhancement. When the artery seemed to be occluded, we measured the e xternal diameter of the ICA (1) on the occluded side, at its upper por tion and most enlarged level, (2) at its lower portion, beyond the bul b, and (3) on the contralateral side, at its upper portion. Results In terobserver agreement was good except for the presence of annular cont rast enhancement. In the stenotic dissection group (n=12), the presenc e of a narrowed eccentric lumen at the upper portion of the ICA on axi al CT images was classified correctly in all cases (sensitivity, 100%; specificity, 100%). An arterial wall thickening was seen in ail cases of dissection but also in three cases of the control group. In the oc clusive dissection group (n=6), the enlargement of the dissected arter y was the best criterion (sensitivity, 100%, specificity, 100%) for oc clusive dissection. Conclusions Helical CT seems to be a reliable meth od for evaluating extracranial ICA dissection. The analysis of the res idual arterial lumen and the measurement of the external diameter of t he carotid artery were the best criteria for the diagnosis. Further st udies with larger groups are required to determine whether ICA dissect ions might be diagnosed using helical CT as a first procedure.