Surgical highways to the craniovertebral junction: Is it time for a reappraisal?

Background: The craniovertebral junction (CVJ) can be affected by a variety of congenital or acquired anomalies. Because of its complexity, a careful evaluation of bones and ligamentous structures in all three planes is required. This can be achieved by studying the CVJ in terms of several anatomical and radiological lines that have been visualized to facilitate understanding of its surgical anatomy. In this study we aimed to review the state-of-the art craniometric CVJ lines and approaches. Methods: In December 2016 a PubMed search was performed, including the search terms ‘CVJ surgical approach/line’, ‘cervical approach’, ‘craniometric measurement’, ‘CVJ anatomy’ and ‘ventral/dorsal/far-lateral approach’. Anatomical and radiological lines and angles evaluated on traditional radiography, computed tomography (CT) scanning or magnetic resonance imaging (MRI) in the axial/sagittal/coronal views were included and described. Results: Several measurements and radiological landmarks were included to evaluate the anatomy of the CVJ. They were fully described and categorized on the basis of the anatomical plan and the surgical or diagnostic purpose they are used for. Conclusion: Among the numerous radiological measurements described, it has been shown that McRae’s line, Chamberlain’s line, McGregor’s line, the Redlund-Johnell method and Ranawat’s line are the most widely used and reliable ones for evaluating skull base craniometry. Secondly, the hard palate line (HPL), nasoaxial line (NAxL) and palatine–inferior dental arch line (PIA) are used to preoperatively assess the ventral endonasal or transoral surgical approaches. Thirdly, the C7 slope has been demonstrated as a reliable predictor of occipitocervical and spinopelvic alignment in CVJ fusion.