An Unusual Case of Unilateral Atlanto-Occipital Assimilation with Skull Asymmetry

A congenital fusion of the atlas to the base of occiput is defined as assimilation of Atlas. This condition is due to failure in segmentation and separation of the most caudal occipital sclerotome and first cervical sclerotome during the first week of fetal life. This is a case of unilateral fusion of left half of atlas with corresponding occipital bone and atlas is rotated and inclined. Skull showed asymmetries in various skull features on left side like change in size of neurovascular foramina, shifting of position of styloid process, reduction in size of middle cranial fossa along with corresponding petrous bone. Hence knowledge of position of various features of skull, beneficial to the clinicians, surgeons, neurologist and radiologist.