Partial aplasia of the posterior arch of the atlas with a persistent posterior tubercle

AGENESIS OF THE POSTERIOR ARCH OF THE ATLAS: AN INCIDENTAL FINDING IN A POLYTRAUMATIZED PATIENT

ABSTRACT The first cervical vertebra is subject to numerous anatomical variations. One of these is posterior arch agenesis, which is classified into five distinct morphological types. Together, all types of posterior arch agenesis comprise only 4% of atlas variations. Furthermore, complete agenesis of the posterior arch associated with the presence of the posterior tubercle is rare. This work reports a case of posterior arch agenesis with the presence of the posterior tubercle in a 33 year-old male victim of a motor vehicle collision. Despite being asymptomatic, this anatomical variation can present with headaches and neck pain. It is mostly found as an incidental finding in imaging studies performed by the emergency team and, as a result, it is often misdiagnosed as a C1 fracture. Knowledge of the variations relating to the first cervical vertebra is therefore essential to avoid delays in diagnosis and treatment of polytraumatized patients. Level of evidence V; Case report.