[Congenital malformations of the atlas: classification and clinical significance].

A classification of congenital anomalies of atlas is proposed in order to make a systematic approach to its radiological diagnosis. Atlas is divided in four areas (posterior arch, union of posterior arch and articulation, articulation and anterior arch) for isolated malformations and two more for occipito-atloid and atlo-axoid anomalies. The common anomalies and its possible clinical relevance in each area are described.