Atherosclerotic plaque at the carotid bifurcation: CT angiographic appearance with histopathologic correlation

Abstract

Background and purpose: The likelihood that carotid plaque will give rise to cerebral ischemia probably relates to the degree of arterial stenosis and to plaque morphology. The aim of this study was to assess whether features seen at CT angiography might be used to predict carotid plaque stability by comparing CT angiograms with histopathologic examinations of the carotid artery bifurcation.

Methods: Nine patients with symptomatic severe carotid stenosis at intraarterial angiography had CT angiography of the carotid bifurcation before carotid endarterectomy. After endarterectomy, multiple sections of the specimens through the carotid bifurcation were examined histologically. Plaque characteristics recorded included the proportion of necrotic/lipid core, presence of hemorrhage, extent of fibrosis, ulceration, calcification, inflammatory cell infiltrate, and fibrous cap thickness. Corresponding CT angiograms were assessed for plaque size, distribution, and radiodensity as well as presence of calcific density and ulceration. Histologic findings and CT angiograms were compared.

Results: Plaque with a large necrotic/lipid core, which was often hemorrhagic, was found in 16 of 23 sections, and in 15 of these this histologic appearance corresponded with patchy or homogeneous low density on CT angiograms. Six of seven predominantly fibrous plaques were of soft-tissue density on CT angiograms. High density consistent with calcification was seen more frequently on CT angiograms than it was detected histologically, but CT angiography depicted plaque ulceration poorly (four ulcers at histology; two false-positive and two false-negative findings at CT angiography).

Conclusion: CT angiography is a promising method for assessing the lumen and wall of the carotid artery. The apparent correlation between histologic appearance and plaque density on CT angiograms has important implications for the prediction of plaque stability, even though ulceration is shown inconsistently.

fig 1.

Low-density plaque. A, CT angiogram of internal carotid artery 1 cm above the bifurcation shows a severe stenosis (black arrow indicates contrast in lumen) caused by a large eccentric hypodense plaque (white arrowheads). The small area of calcification (open arrow) was not detected on the histologic section. B, Corresponding histologic section shows a large necrotic core (N). The fibrous cap is intact at this level but of variable thickness; at O, it is thinned, and higher power showed superficial inflammation. S indicates the site of surgical incision.

fig 2.

Mixed-density plaque. A, CT angiogram of the proximal internal carotid artery shows a predominantly intermediate-density plaque with foci of hypodensity (arrowheads). Curved arrow indicates internal jugular vein. B, Corresponding histologic section shows an irregular slitlike lumen (Lu) separated by a reasonably thick fibrous cap (C) from a large necrotic core (N) comprising necrotic and lipid debris as well as thrombus. S indicates surgical incision.

fig 3.

Plaque ulceration. A, CT angiogram of the common carotid artery 1 cm below the bifurcation shows circumferential arterial wall thickening, with a focal contrast-containing defect interpreted as an ulcer (arrow). B, Corresponding histologic section shows a ruptured fibrous cap (C) with a mixture of necrotic debris (A) and thrombus (T) projecting into the lumen (Lu).