Morphology Analyses of Human Carotid Plaque in Assessing Fibrous Cap Rupture Risk

The sudden rupture of a vulnerable arterial plaque is a major cause of cerebral ischemic event, and is normally triggered by unfavorable plaque morphology. The aim of our study was to compare carotid plaque morphology between ruptured and non-ruptured plaques to improve our understanding about the risk of human arterial plaque rupture.

Histological assessment was carried out on 18 carotid plaques obtained from carotid endarterectomy. Plaque geometry parameters such as fibrous cap thickness, lipid core size, and collagen content were analyzed. In addition we analyzed the macrophage distribution in the plaque. The results from ruptured/non-ruptured plaques were compared and analyzed.

For ruptured plaques (n=10) the mean minimum cap thickness was 302±181 microns (IQR 195 to 434 microns), compared with 358±229 microns (IQR 256 to 460 microns) for non-ruptured plaques (

p

=0.23). Mean collagen content was 40.1% for ruptured plaques, compared with 49.3% for non-ruptured plaques (

p

=0.08). Further to this, the mean collagen content in the adjacent region of the fibrous cap rupture site for the ruptured plaque group was found to be 6.6±5.2%. The mean maximum lipid core thickness in ruptured plaques was 904 microns (IQR 690 to 1183micron) compared with 549 microns (511 to 586 micron) for non-ruptured plaques (

p

=0.02). The mean area occupied by macrophage cells in the upstream and downstream transversal planes was 1.21±0.86mm

2

and 5.14±1.88mm

2

in ruptured plaques (

p

=0.0079), compared with 1.255±1.38mm

2

and 4.62±1.86mm

2

respectively in non-ruptured plaques (

p

=0.0087).

This study demonstrates the morphological difference between ruptured and non-ruptured plaques. This information may be used as a stepping stone to improving our understanding on the risk assessment of human arterial plaque rupture.