Imaging the craniocervical junction.

INTRODUCTION: The craniovertebral junction (CVJ) comprises the occiput, atlas, and axis. Radiographic evaluation of this region involves knowledge of only a few anatomical landmarks, as well as basic normal measurements and relationships to perform CVJ craniometry. Occipital bone anomalies and atlanto-occipital non-segmentation typically produce basilar invagination. Atlas anomalies predominantly involve the posterior arch, while the os odontoideum accounts for the majority of axis anomalies. RESULTS AND DISCUSSION: A number of syndromes are associated with CVJ pathology, the most notable being Klippel-Feil and Down syndromes, achondroplasia, the mucopolysaccharidoses, and osteogenesis imperfecta. Skull-base softening associated with some of these syndromes results in acquired basilar invagination or basilar impression. In this article, we present a detailed review of essential anatomy and craniometry needed for radiographic assessment of the CVJ and illustrate various congenital anomalies of the occiput, atlas, and axis. The common syndromes affecting this region are also discussed and illustrated.