Manifestations of occipital vertebrae - Its embryological and clinical significance

Background: Manifestations of the occipital vertebrae in the region of anterior rim of foramen magnum, either in the midline and/or laterally are due to failure of segmentation of the proatlas. The proatlas is derived from the fourth occipital sclerotome. There is a broad spectrum of occipital vertebrae variations which includes: third occipital condyle (condylus tertius), basilar process, paracondylar process and prebasioccipital arch (hypocondylar arch). These manifestations, if present can cause brainstem myelopathy and lower cranial nerves palsy during first and second decades of life. Materials and Method: Two hundred dry adult human skulls of Indian origin were studied in the Department of Anatomy, M.S Ramaiah Medical College. The base of these skulls was observed for presence of remnants of occipital vertebrae. Results: Out of 200 skulls, 4 skulls showed remnants of occipital vertebrae (2%). Median occipital condyle was observed in one skull (0.5%), hypocondylar arch was observed in one skull (0.5%), bilateral basilar process in one skull (0.5%) and bilateral paracondylar process in one skull (0.5%). Conclusion: The knowledge of manifestations of occipital vertebrae is important for the radiologists during interpretation of radiographic images of the craniovertebral junction to make a distinctive diagnosis of its diseases and the neurosurgeons while doing skull base surgeries. An attempt has been made in the present study to throw light on the various manifestations of occipital vertebrae, its embryological and clinical significance.