Posterior midline cleft of the atlas – a crucial anatomical variation in vertebral fractures

The anatomy of the first vertebra, namely atlas, has significant clinical implications. Atlas is situated between the occipital bone and the second cervical vertebra (axis) and is one of the main points of head movement. Most congenital anomalies of the vertebra are diagnosed incidentally during imaging investigations and can be associated with cervical spine anomalies. The neurological symptoms may include weakness in the four limbs, acute neurologic deficits such as transient quadriparesis, paraparesis, Lhermitte's sign, chronic neck pain, and headache. This anomaly is also commonly seen in gonadal dysgenesis, Klippel-Feil syndrome, Arnold-Chiari malformations, and Turner and Down syndrome. Unlike other variations, which arise due to disturbances of ossification posterior midline clefts of the atlas, are different since they are a developmental failure of chondrogenesis. We therefore present an anatomical case and analysis of the literature about posterior arch clefts of atlas.