RELIABILITY AND AGREEMENT IN THE CEREBELLAR TONSIL TIP LOCALIZATION: TWO METHODS USING THE MCRAE’S LINE CONCEPT IN MRI

Abstract

Background: The cerebellar tonsil tip position (TP) is a common parameter used for the radiological diagnosis of Chiari malformation type I (CM). However, this paramedian structures is usually not properly visualized in the midsagittal section. Such mismatch may be a source of bias in TP measurements based on the McRae’s line traced between median craniometric points. This study aims to evaluate the intra and interoperator reliability and agreement of two protocols to trace the McRae’s line in MRI for the cerebellar tonsil tip localization, adding a three-dimensional multiplanar reconstruction (MPR) approach to the midsagittal plane. Methods: Sixty-two T1- weighted head MRIs were obtained for 32 CM patients and 30 controls. Two operators independently applied two TP measurement protocols, one considering only the visualization of the sagittal plane and the other using MPR. The intraclass correlation coefficient was used to assess intra and interoperator reliability, and the Bland-Altman graphical method to evaluate the agreement between the measurement protocols. Results: The sagittal method significantly underestimated McRae's line and tonsillar herniation when compared to the MPR method. The MPR method provided better reliability of the McRae’s line measurement when compared to the sagittal method, but this did not influence the reliability of the TP. Analysis of the Bland-Altman plot showed that the limits of agreement were close to acceptable for the McRae’s line, but not for measures of TP. Conclusion: It is possible that the greater precision in tracing the McRae’s line by the MPR method provides a better standardized measurement of the TP.