Atlas posterior arch and vertebral artery's groove variants: a classification, morphometric study, clinical and surgical implications.

Abstract

The third part of the vertebral artery (VA) coursing in vertebral artery groove (VAG) may be injured during posterior craniocervical junction approaches. The current study classifies all possible variants of the posterior arch (PA) of the atlas vertebra (C1), focusing on VAG and calculates their incidence. PA and VAG morphometry is studied in correlation with gender and age. Clinical and surgical implications of recorded variants are provided in an effort to explain associated pathology. The usefulness of three-dimensional computed tomography (3D-CT) in detecting PA variants is highlighted. Two hundred and forty-four Greek adult dry C1 were classified in types according to PA morphology [i.e. presence of an imprint or a distinct VAG and occurrence of a partially or completely ossified dorsal (PDP or CDP) or lateral (PLP or CLP) ponticle unilaterally or bilaterally]. Combined variants were also included. A VAG and an imprint were detected in 42.62% and 15.16%. A PDP and CDP were observed in 18.03% and 15.98%, while a CLP and PLP in 2.05% and 1.64%, respectively. Combined PDP and PLP were detected in 2.05%, a CDP and CLP similarly to a CDP and PLP in 1.23% and a PDP and CLP in 0.40%. Variants' classification will contribute to an in depth understanding of the complex C1 anatomy and may explain cases of VA entrapment and injury during PA fixation. Surgeons should carefully study 3D-CT imaging to ensure type, location, size and shape of C1 ponticles in combination with VAG morphology and VA course before screw insertion.