Relationship between Calcification and Vulnerability of the Carotid Plaques

Carotid plaques with a high degree of calcification are usually considered at low embolic risk. However, since a precise evaluation of the extent of calcification is not possible preoperatively through duplex ultrasound and postoperatively by conventional histological examination due to the decalcification process, the relationship between the amount of calcium involvement and plaque vulnerability has not been evaluated yet. This study aims to correlate the extent of carotid plaque calcification with clinical, radiological, and histological complications.

Symptomatic and asymptomatic consecutive patients submitted to carotid endarterectomy between January to December 2014 were included in the study. The amount of carotid calcification was assessed at preoperative computed tomography (CT) through measurement of thickness and circumferential calcium extension and graded from 1 to 8 accordingly (Babiarz classification). Patients were then categorized into 2 groups (low-level group: grade 1-5; high-level group: grade 6-8) and correlated with clinical characteristics and ipsilateral cerebral ischemic lesions at CT. Vulnerability of the plaque was assessed histologically according with American Heart Association (AHA) Classification. Results were overall blindly correlated.

One hundred five patients (81% male; age: 73 ± 8 years) were enrolled in the study. Forty (38%) were symptomatic and 43 (40%) had an ipsilateral focal lesion at preoperative cerebral CT. Thirty-six (38%) patients had high-level carotid calcification degree at CT scan. At histological analysis, 56 (56%) plaques were considered complicated (AHA type VI). Patients with high-level and low-level carotid calcification had similar epidemiological risk factors, preoperative neurological symptoms, and histological complications (17% vs. 15%, P = 0.76 and 50% vs. 55%, P = 0.62, respectively). The high-level calcification group showed a significantly higher incidence of ipsilateral cerebral lesions at preoperative CT (56% vs. 32%, P = 0.01).

A high level of calcification of the carotid plaque is not necessarily associated with lower vulnerability: the incidence of preoperative neurological symptoms and histological complications is similar in patients with and without extensive carotid plaque calcification. Cerebral ischemic lesions may be even more frequent in the presence of highly calcified plaques.