What the mind does not know, the eyes do not see: a rare congenital fusion of the odontoid process to the atlantal hemiarch.

Congenital spinal fusion of an odontoid process to an atlantal hemiarch is very rare. The unfamiliarity of the medical fraternity with this congenital malformation can easily be mistaken for an acute fracture, chronic infection or inflammatory disease. We present our experience of managing an adult who presented with neck pain after a motor vehicle accident. Radiological investigation revealed congenital fusion of the odontoid process to the atlantal hemiarch. The prevalence, embryology and clinical significance of this anomaly are discussed. As the natural progression of this anomaly is not well documented, we suggest periodic follow-up to monitor the progression of degenerative changes and instability of the occipitoatlantal junction.