An Osteological Study of Occipitocervical Synostosis: Its Embryological and Clinical Significance

Abstract

Background: 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.Material and Methods: 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 atlantooccipital 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.

Anomalous vertebral arteries in Klippel-Feil syndrome with occipitalized atlas: CT angiography

“…OA per se has been reported in about 0.08%-3% of the general population [3] and is in up to 30%-50% cases of KFS [1] . The foramen magnum in cases of OA is often found to be severely impaired, especially when associated with basilar invagination; this is associated with increased risk of compressive brainstem and cord injury.…”

Anatomical Variant of Atlas : Arcuate Foramen, Occpitalization of Atlas, and Defect of Posterior Arch of Atlas

“…In this study, the incidence of occipitalization of the atlas was 0.097%. The synostosis has been classified into four types based on the zones of the atlas fused with the occiput 23) . Zone 1 fusion involves the anterior arch of the atlas in front of the lateral masses (20% of cases).…”

“…Occipitocervical synostosis results in a shift of the first mobile segment between the skull and spine to the C1–2 junction. This causes stress and a restricted range of movement, as a result of which there may be overstretch failure of the supporting myoligamentous structure, leading to a gradual loosening of the atlantoaxial joint with progressive atlantoaxial subluxation 23) . Compression of the spinal cord or the brain stem because of occipitocervical synostosis can produce signs and symptoms varying from a simple headache to a full blown neurological syndrome 31) .…”

“…Partial type was considered as partial arcuate foramen which was noted as a distinct bony spicule extending from the superior articular facet overhanging the dorsal arch. Assimilation of the atlas was classified in accordance with criteria specified by Mudaliar et al 23) . Zone 1 fusion involves the anterior arch of the atlas in front of the lateral masses.…”

Atlas occipitalisation associated with other anomalies in a 16th century skeleton from Sardinia (Italy)

“…The congenital anomaly has a current incidence of 0.67% to 3.63% in Asian populations, without a sex predilection [13]; in Caucasians the incidence is lower, being 0.5% to 1% [6]. In modern clinical practice this condition is usually an incidental or autoptic finding [1].…”