Basilar Invagination Diagnosis, Classification, and Radiology

STUDY DESIGN: A systematic literature review and consensus using Delphi method. OBJECTIVE: This review aimed to analyze recent literature on diagnosis, classification, and radiologic characteristics of Basilar Invagination (BI) to generate recommendations on these topics. SUMMARY OF BACKGROUND: Basilar invagination diagnosis, classifications, and radiologic characteristics evolved during the last decade; however, many debatable criteria disturb a common language fundamental to compare clinical research. MATERIAL AND METHODS: The WFNS Spine Committee organized two separate consensus meetings to discuss and create statements that were voted on to reach a consensus. RESULTS: Basilar invagination mainly results from a CVJ developmental abnormality and is often associated with congenital anomalies. There is also an acquired type that occurs by bone softening, such as rheumatoid arthritis. It can be classified as type I (atlantoaxial dislocation) and type II (without atlantoaxial dislocation) basilar invagination. Clinical signs may either be due to brainstem compression or cervical spinal cord compression and instability. Although many radiologic measurements are proposed, the most reliable ones are the McRae line, Chamberlain line, and Boogard angle. CONCLUSIONS: Diagnosis of basilar invagination should be made by midsagittal craniocervical x-rays, CTs or MRI. There are two types of basilar invagination: type I basilar invagination is associated with instability, and treatment can focus on stabilization. However, type II basilar invagination may need decompressive surgeries.