Bony bridges and selected variations of the first cervical vertebra (Atlas): A brief encyclopedic overview with comments on clinical and neurological implications

Background The first cervical vertebra, the atlas (C1), is a unique and complex structure responsible for supporting the skull and facilitating head movement. Due to its intimate anatomical relationship with the vertebral artery and cervical nerves, any variation in its morphology—particularly the presence of bony bridges—may have important clinical consequences. Aim This brief encyclopedic overview summarizes the anatomy of the atlas, its most common bony bridge variants, and their potential clinical significance, particularly in neurology and cervical spine surgery. Conclusions Bony bridges involving the atlas, such as the arcuate foramen and retrotransverse canal, are common anatomical variants with potentially significant clinical implications. While often asymptomatic, these variants can affect vascular and neural structures, contribute to symptoms such as headache or vertigo, and complicate surgical procedures in the craniocervical region.