The bony components of the craniovertebral junction (CVJ) have been investigated in 172 skeletons, dug up from several archaeological sites, to define the frequency of developmental dysmorphisms, and to acquire qualitative and quantitative data about their morphology. A review of the pertinent literature is also presented. Twenty-five individuals (14.5%) exhibited at least one dysmorphism, which ranged from a condition of simple variant to a true malformation. Four individuals presented two or more anomalies at the same time (2.3% of the whole sample, 16% of the affected individuals). The most frequently observed abnormalities were: (i) the presence of a complete bony bridge in the atlas, forming a canal surrounding the vertebral artery (arcuate foramen, supertransverse foramen, and the simultaneous occurrence of arcuate foramen and supertransverse foramen); (ii) the presence of basilar processes. Basilar processes displayed a great variety in shape and dimension. They also differed with respect to their relationship with atlas and axis. The less frequently detected anomalies were: (i) complete absence of the posterior arch of C1, (ii) fusion of C2 and C3, and (iii) irregular segmentation of C2. A broad array of structural defects has been described at the CVJ. They may occur either isolated or as part of complex multisystem syndromes. Although harmless in many cases, they can notwithstanding cause severe, even life-threatening complications. When unrecognized, they may generate trouble during surgery. Hence, accurate knowledge of CVJ arrangement, including its multifarious variations, is a critical issue for radiologists, clinicians, surgeons, and chiropractors.
