Symmetry, asymmetry and hypoplasia of the intracranial internal carotid artery on magnetic resonance angiography.

OBJECTIVE The aim of this study was to determine the prevalence of symmetry, asymmetry and hypoplasia of the intracranial internal carotid artery (ICA), and the possible presence of other variants of the ICA by magnetic resonance angiography (MRA). SUBJECTS AND METHODS This prospective-retrospective study included 1000 subjects who underwent consecutively MRA of the cerebral arteries. 3D-time of flight angiograms were performed according to the standard protocol. We measured the diameter of the ICA and the diameter of the A1 segment of the anterior cerebral artery (ACA). The symmetry, asymmetry and hypoplasia of the ICA, as well hypoplasia of the A1 segment of the ACA were analysed using the vascular asymmetry coefficient. RESULTS The right and left ICA were symmetrical in 93.9% examinees, and asymmetrical in 6%, while ICA hypoplasia was found in only one patient (0.1%). Other variants of the ICA were not found. There was no significant difference in the prevalence of individual variations between male and female patients, and no significant frequency difference was found between anatomical variations in terms of the right and left ICA. In 38.3% patients with asymmetrical ICAs, aplasia or hypoplasia of the A1 segment of the ACA was found on the side of the ICA with a reduced diameter. CONCLUSION Congenital hypoplasia of ICAs is a very rare abnormality, while asymmetry of ICAs is more common. After evaluating severe asymmetry of intracranial ICAs by MRA, MRA of the neck is recommended, especially in patients with a complete anterior part of the circle of Willis.