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

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. 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. 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. • The article reviews atlas (C1) anatomical variations, focusing on bony bridges like the arcuate foramen and retrotransverse canal. • Clinical relevance is explored, especially how these bony bridges may influence vertebral artery or cause neurological symptoms. • Morphology and prevalence of arcuate foramen and retrotransverse canal are analyzed, with emphasis on surgical and radiological relevance. • The study highlights the need to recognize C1 variants during imaging and surgery to prevent misdiagnosis or procedural complications.