Atlantooccipital Fusion: Prevalence and its Developmental and Clinical Correlation

Atlantooccipital fusion or occipitalization of atlas or assimilation of atlas is a rare or uncommon abnormality recorded in anatomical, morphological and radiological studies. It is usually associated with reduction in dimensions of foramen magnum leading to acute or chronic neurovascular compression and clinical manifestations of varying severity. Though, atlantooccipital fusion is rare but it is important and significant for the physicians and surgeons for their diagnostic and therapeutic approach.

To know the prevalence of atlantooccipital fusion in South Asian population predominantly in Central India and its embryological and clinical correlation by reviewing literature and earlier studies.

This study included careful examination for the atlantooccipital fusion on total 192 human skulls of both genders, available in the Department of Anatomy AIIMS Raipur, Chhattisgarh, India, Department of Anatomy and Forensic Medicine of Gandhi Medical Colledge, Bhopal, Madhya Pradesh, India and Pt. Jawahar Lal Nehru Memorial Medical College, Raipur. Morphometric measurements of the abnormal skulls were done, analysed and recorded. Observations and findings of this study were correlated embryologically and clinically with the results and claims of previous studies and literature, and accordingly the conclusions were drawn.

We found only two skulls with atlantooccipital fusion, in overall study of 192 skulls. The first skull showed incomplete atlantooccipital fusion on the left side with little right lateral inclination and missing posterior tubercle/spinous process and adjoining part of posterior arch of atlas, whereas the second skull showed complete atlantooccipital fusion.

We conclude that the prevalence of atlantooccipital fusion including complete and incomplete fusion was 1.04%, which is higher than the proclaimed prevalence rate of 0.12% to 0.72%, by the previous studies. In accordance with the fact that the atlantooccipital fusion represents a synostosis between the atlas and the occipital bone due to developmental abnormal segmentation of cranial part of paraxial mesoderm and abnormal fusion between segments of caudal occipital and cranial cervical sclerotomes, we would like to thereby assert that the fusion associated with the reduction in dimensions of foramen magnum (reduction also seen in our study) is definitely significant for diagnostic and therapeutic purposes to clinicians.