Computed Tomographic Distinction of Intimal and Medial Calcification in the Intracranial Internal Carotid Artery

Abstract

Background: Intracranial internal carotid artery (iICA) calcification is associated with stroke and is often seen as a proxy of atherosclerosis of the intima. However, it was recently shown that these calcifications are predominantly located in the tunica media and internal elastic lamina (medial calcification). Intimal and medial calcifications are thought to have a different pathogenesis and clinical consequences and can only be distinguished through ex vivo histological analysis. Therefore, our aim was to develop CT scoring method to distinguish intimal and medial iICA calcification in vivo.

Methods: First, in both iICAs of 16 cerebral autopsy patients the intimal and/or medial calcification area was histologically assessed (142 slides). Brain CT images of these patients were matched to the corresponding histological slides to develop a CT score that determines intimal or medial calcification dominance. Second, performance of the CT score was assessed in these 16 patients. Third, reproducibility was tested in a separate cohort.

Results: First, CT features of the score were circularity (absent, dot(s), <90°, 90-270° or 270-360°), thickness (absent, ≥1.5mm, or <1.5mm), and morphology (indistinguishable, irregular/patchy or continuous). A high sum of features represented medial and a lower sum intimal calcifications. Second, in the 16 patients the concordance between the CT score and the dominant calcification type was reasonable. Third, the score showed good reproducibility (kappa: 0.72 proportion of agreement: 0.82) between the categories intimal, medial or absent/indistinguishable.

Conclusions: The developed CT score shows good reproducibility and can differentiate reasonably well between intimal and medial calcification dominance in the iICA, allowing for further (epidemiological) studies on iICA calcification.

Fig 1. Intimal calcification in the intracranial internal carotid artery (iICA) on a coronal brain CT image (left) and on a histological slide (right).

On CT a blue circle is placed around the iICA. In histology the intimal calcification area is light blue and the calcification area of the internal elastic lamina indicated by the black line.

Fig 2. Internal elastic lamina calcification in the intracranial internal carotid artery (iICA) on a coronal brain CT image (left) and on a histological slide (right).

On CT a blue circle is placed around the iICA. Calcification area of the internal elastic lamina is indicated by the black line. Reprinted from A. Vos et al. Stroke. 2016;47:221–223 (Fig 1A) under a CC BY license, with permission of the American Heart Association, original copyright 2016 American Heart Association.

Fig 3. Intracranial internal carotid artery calcification (iICA) score with Circularity (Dot, <90°, 90–270° and 270–360°); Thickness (Thick ≥ 1.5mm and Thin < 1.5mm) and Morphology (Indistinguishable, Irregular, Continuous).

Calcifications are highlighted (light blue). In these examples all images are in the axial viewing plane except for the <90° and 90–270° images which are in the coronal plane.