Occipitalization of the atlas is an osseous anomaly of the craniovertebral junction.
The aim of this paper is to present an anatomical variant of the fused atlas
with the occipital bone and discuss similar cases described in literature. The
skull of an adult male analysed in this study belonged to the cranial collection
of the Department of Anatomy of the Jagiellonian University, Medical Collage.
A tight bony fusion between the anterior arch of the atlas, the left portion of
the posterior arch, the lateral masses of the atlas, and the occipital bone was
observed. Hence, the left and right superior articular facets of the atlas were
fused with the corresponding occipital condyles. The anteroposterior dimension
of both inferior articular facets was the same (20 mm), while the transverse
diameter of the right one was considerably smaller (12 mm). The transverse
diameter of the left inferior articular facets was 17 mm. The right and the
left transverse process of the atlas were normally developed, each of them
contained transverse foramen, and they were not fused with the occipital bone.
The circumference of the foramen magnum was minimally diminished by the
osseous structures of the atlas fused to the occipital bone. The sagittal and
transverse diameters of the foramen magnum (38 mm x 34 mm) were within
the normal range of variation. However, the asymmetrical anatomy of the inferior
articular facets of the atlas give rise to speculation that movement in the
atlantoaxial joint was disturbed by assimilation with the occipital bone. (Folia
Morphol 2010; 69, 3: 134-137
