An osteological study of occipitocervical synostosis: its embryological and clinical significance

Synostosis or fusion of atlas with occipital bone is known as occipitocervical synostosis, occipitalization of the atlas, or atlanto-occipital fusion. This is a rare congenital malformation at craniovertebral junction. Its incidence ranges from 0.08%-3% in general population. Occipitocervical synostosis 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. Hence, the present study was undertaken to determine the incidence and to describe the morphology of the occipitocervical synostosis. Two-hundred dry adult human skulls of Indian origin were studied in the Department of anatomy. The base of these skulls was observed for presence of atlanto-occipital fusion. The anteroposterior and transverse diameter of the foramen magnum and diameter of the inferior articular facets were measured in these skulls using digital vernier caliper. Two skulls showed occipitalization of Atlas (1%). One of the skulls showed partial fusion (0.5%) while the other showed complete occipitalization (0.5%). The knowledge of bony fusion between the cranial base and the first cervical vertebra is important as such skeletal anomaly may result in sudden unexpected death due to compression of the vital structures such as brain stem and vertebral arteries.