Background and Objectives: The asymmetrical vertebral artery (VA) flow and diameter
are common findings, which can result in an asymmetrical blood flow in the basilar
artery (BA), leading to bending of the artery over time. This study investigated whether
the variation of the different vertebrobasilar morphological indices that influence
flow characteristics might be inherited. Materials and Methods: We analyzed 200 cerebral
magnetic resonance imaging (MRI) scans of healthy Caucasian twins (100 pairs) who
underwent time-of-flight MRI. From the scans, we reconstructed the 3D mesh of the
posterior circulation from the start of the V4 segment to the basilar tip and subsequently
analyzed the morphology of the vertebrobasilar system. The phenotypic covariances
of the different morphological parameters were decomposed into heritability (A), shared
(C), and unshared (E) environmental effects. Results: 39% of the twins had left dominant
VA, while 32.5% had right dominant. In addition, 28.5% were classified as equal. The
vertebral artery V4 segment diameter, curvature, and tortuosity were mainly influenced
by shared (C) and unshared (E) environmental factors. A moderate heritability was
found for the BA length (A: 63%; 95% CI: 45.7-75.2%; E: 37%; 95% CI: 24.8-54.3%) and
volume (A: 60.1%; 95% CI: 42.4-73.2%; E: 39.9%; 95% CI: 26.8-57.6%), while the torsion
of both arteries showed no heritability and were only influenced by the unshared environment.
Conclusions: The length and volume of the BA show a moderate genetical influence.
However, most of the measured morphological indices were influenced by shared and
unshared factors, which highlight the role of the ever-changing hemodynamic influences
shaping the geometry of the vertebrobasilar system.
