Occipitalization of the atlas vertebra: it’s embryological and clinical signifcance

Background: The atlas is the first cervical vertebra, commonly called C1. Occipitalization of the atlas, occipitocervical synostosis, or atlanto-occipital fusion is one of the most common skeletal abnormalities of the upper cervical spine. Its incidence ranges from 0.08%-3% in general population. Occipitalization of the atlas result in narrowing of foramen magnum which may compress the brain stem, vertebral artery and cranial nerves. Knowledge of occipitocervical synostosis is important for the surgeons during the surgeries in the craniovertebral region.
Methods: In the present study a sample of 84 adult human skulls were examined in the
department of Anatomy, Shyam Shah Medical College, Rewa (MP), for evidence of atlanto-occipital fusion. For the study non pathological adult skulls of unknown sex were included.
Results: Total two specimens exhibited occipitalization of atlas. One specimen exhibited atlanto-occipital fusion, in which the total fusion of the atlas vertebra with the skull was seen. It also exhibited large anterior tubercle and hypoglossal canal was present only on right side. In another specimen, anterior arch of the atlas along with the anterior tubercle was completely fused with the anterior rim of foramen magnum of the occipital bone except for a slit-like opening above the left anterior arch of atlas near the anterior tubercle. It also exhibited hypoglossal canal on both sides with normal size and shape.
Conclusions: The partial or complete assimilation of the atlas may have resulted due to disruption in the separation of the caudal part of the first sclerotome from the cranial part of the first sclerotome. The knowledge about pre existing malformations and their clinical and radiological appearance is important during diagnostic imaging studies. This condition may also be of importance to physiotherapist dealing with the neck pain.