Atlantooccipital assimilation associated with combined atlas arch defect: a radiological case report

In this report, atlantooccipital assimilation (AS), anterior arch defect (AAD), and posterior arch defect (PAD) of theatlas, and several variations around the craniocervical junction were identified on computed tomography (CT) of a patientof unknown sex and age. Coronal and sagittal CT scans showed AS and bilateral fusion of the atlas and the base of occipitalbone. Axial CT scan at the atlas revealed PAD type B on the left side and midline AAD. Morphometric measurementsindicated a potential ventral spinal cord compression. In addition, mid-sagittal CT revealed the presence of fossa navicularismagna and incomplete formation of the transverse foramen on the right side. This study reports an extremely rare ASassociated with AAD, PAD, and other variations of the clivus and the atlas. To our knowledge, no similar case has beenreported in the literature.