OCCIPITALISATION OF ATLAS VERTEBRA AND ITS CLINICAL FRAMES OF REFERENCE- AN ANALYSIS

Abstract

Vertebral column is made of 33 vertebrae named as cervical, thoracic, lumbar, sacral and coccygeal vertebrae. Axial skeleton comprises of skull and vertebral column. 12 pairs of cranial nerves and 31 pairs of spinal nerves exit from the central nervous system which control the entire body. Malformations or fusion of vertebrae could be one of the etiologies of nerve compression syndromes. Vital structures emerge out through intervertebral foramina extending from cervical to coccygeal vertebrae. Occipitalisation of atlas, the first cervical vertebra is one of the emergencies leading to wide spectrum of presentations like chronic neck pain or foramen magnum syndrome or unconscious state due to compression of medulla oblongata. During routine examination of skull bones while teaching, one skull was found to exhibit assimilation of atlas. Photographs were captured and compared with normal skull. Thorough examination revealed incomplete occipitalisation of atlas. The anterior arch was completely fused but the posterior arch was bifid showing a split. The styloid process on right side seemed to be long and very close leading to compression of structures of styloid apparatus in addition. On observation, it was found to be a male skull. Fusion of vertebrae may be a congenital anomaly due to maldevelopment of somites in forming vertebrae. Skeletal element of caudal 4th occipital somite forms the occipital bone and when it is fused with the proximal 1st cervical somite leads to occipitalisation of atlas. Acquired conditions like atlantoaxial subluxation, chiari malformations or cervical vertebral fusion or foramen magnum abnormalities have been associated with assimilation of atlas. The present study reports occipitalisation of atlas which is incomplete with a bifid posterior arch. Prevalence of such anomalies may form the differential diagnosis of chronic headache or myelopathies.