Prevalence of primary basilar invagination among asymptomatic Sri Lankan adults - computed tomographic study

Objective: To evaluated the prevalence and some associated factors of basilar invagination (BI) in a group of Sri Lankan adults. Material and methods: Brain computed tomographic images (CT) of adults admitted to Teaching Hospital Rathnapura, Sri Lanka were studied, excluding subjects with craniofacial syndromes, cerebral or spinal pathologies. The distance between Chamberlain's line (CL) and odontoid process (OP) measured in sagittal CT images (bone window). BI is defined when the OP is 2mm above CL. Results: The study group (n=135; male=67; female=68) was in 20-97 years age range (mean-56±18 years). BI was present in 11.8% (n=16), of which the mean position of OP was 2.33±1.06 cm above CL (range=0.6-4.7 mm). In 13.4%, OP was at the same level as CL. When BI is absent, the mean position of OP was 2.1±1.9 cm below CL. The OP was below CL in 86.6% (n=58) of males and 75% (n=51) of females demonstrating no significant (X2=2.904;p=0.088) gender variation in BI. Internal cranial height (OR=0.823; 95%CI=0.678-0.990; p=0.044) was negatively associated with the incidence of BI. However, age (OR=1.015; 95%CI=0.984-1.047; p=0.341), gender (OR=0.707; 95%CI=0.226-2.218; p=0.553), posterior fossa height (OR=0.912; 95%CI=0.808-1.030; p=0.136), or Klaus' height index (OR=1.099; 95% CI=0.874-1.383; p=0.419) had no significant influence on BI. Conclusion: Current study, for the first time, documents the incidence of BI among asymptomatic Sri Lankans. Since ethnic variation in the incidence of BI is reported, such populationspecific data would be invaluable in diagnosing the asymptomatic BI cohort, which in turn, will facilitate to prevent permanent disability and lifethreatening emergencies.