Atlanto-occipital assimilation: embryological basis and its clinical significance.

Atlanto-occipital assimilation is an osseous embryological anomaly of the craniovertebral junction in which the atlas (C1) is fused to the occiput of skull. Embryologically, this assimilation may happen due to failure of the segmentation and separation of the caudal occipital and the cranial cervical sclerotome. The segmentation clock is maintained by NOTCH and WNT signalling pathways along with Hox genes and retinoic acid. This condition is likely to be a consequence of mutation in above mentioned genes. The knowledge of this assimilation may be crucial for the clinicians as it may lead to various neurovascular symptoms. The present case report involves the analysis of atlanto-occipital assimilation with its clinical significance and embryological basis.