Clivodens Angle: A New Diagnostic Method for Basilar Invagination at Computed Tomography.

STUDY DESIGN: Retrospective study.

OBJECTIVE: To investigate whether clivodens angle (CDA) could diagnose basilar invagination (BI) at computed tomography (CT).

SUMMARY OF BACKGROUND DATA: Over the years, multiple craniometric methods such as Chamberlain line, McGregor line, McRae line, Wackenheim clivus baseline, and Welcher basal angle have been described for evaluation of craniovertebral junction anomalies, initially with radiography and later with CT. However, such a variety of measurements in turn reflects the difficulty in making a definite diagnosis of BI and there is a certain disadvantage in all of these criteria because the anatomic landmarks vary within a normal range.

METHODS: CDA, described an angle formed at the intersetion of a line that runs along the long axis of the clivus and one that runs along the long axis of the dens, was measured on mid-sagittal reconstructed CT images from 63 BI patients and 100 control participants to compare the two groups by using independent-sample t test. Interobserver reliability was evaluated with Kendall correlation coefficient. For evaluating the diagnostic performance and determining the cutoff value of CDA, receiver operating characteristic curve was utilized.

RESULTS: The measurement of CDA showed good interobserver agreement (KCC = 0.891). Compared with control participants whose mean value was 135.8 degrees ± 9.2 (range, 118-156°), BI patients had a significantly smaller one (P < 0.001), 110.4 degrees ± 15.8 (range, 55-140°). The area under receiver operating characteristic curve was 0.937 (95% confidence interval: 0.901, 0.973), and the cutoff value of 125 degrees had the largest Youden index (J), 0.715.

CONCLUSION: Having a better diagnostic performance than clivoaxial angle, CDA can be utilized for diagnosing BI.

LEVEL OF EVIDENCE: 3.