Atlanto-Occipital Fusion With Complete Absent Atlas Posterior Arch and Complete Ossified Caroticoclinoid and Anterior Interclinoid Ligaments

The skull base exhibits numerous morphologic variants, some of which are uncommon and hold clinical significance. The imaging report presents a rare instance of multiple skull base variants identified incidentally through a computed tomography (CT) scan of a 53-year-old female patient. The findings revealed a bilateral partial atlanto-occipital fusion (AOF), an absent C1 posterior arch, and a complete bilateral ossification of the caroticoclinoid and anterior interclinoid ligaments in the form of bars (CCBs and AIBs). This distinctive combination of variants has not been emphasized in existing literature. Recognizing these morphologic variants is essential for preoperative planning to mitigate the risk of neurovascular injury during skull base procedures. This case underscores the necessity of comprehensive anatomic assessment via CT imaging to detect intricate skull base alterations. Acknowledging these rare coexisting congenital abnormalities is crucial for enhancing patient outcomes within clinical and surgical frameworks.