Reliability and Agreement in the Cerebellar Tonsil Tip Localization: Two Methods Using the McRae Line Concept in MRI.

Area of Science:

• Radiology
• Neurosurgery
• Medical Imaging Analysis

Background:

• Cerebellar tonsil tip position (TP) is crucial for diagnosing Chiari malformation type 1 (CM1).
• Standard midsagittal MRI views often lack clear visualization of paramedian structures, potentially biasing TP measurements using the McRae line (ML).
• This limitation necessitates exploring improved methods for accurate ML tracing and TP localization.

Purpose of the Study:

• To evaluate the reliability and agreement of two McRae line (ML) tracing protocols for cerebellar tonsil tip (TP) localization in Chiari malformation type 1 (CM1) diagnosis.
• To compare a standard sagittal plane approach with a 3D multiplanar reconstruction (MPR) approach using MRI.
• To assess intraoperator and interoperator variability in ML and TP measurements.

Main Methods:

• Sixty-two T1-weighted head MRIs from 32 CM1 patients and 30 controls were analyzed.
• Two operators independently applied two ML tracing protocols: one using only the sagittal plane and another incorporating MPR.
• Intraclass correlation coefficient and Bland-Altman analysis were used to assess reliability and agreement.

Main Results:

• The MPR method provided more reliable ML measurements compared to the sagittal-only method.
• The sagittal method significantly underestimated ML and tonsillar herniation.
• While MPR improved ML reliability, it did not significantly enhance TP measurement reliability, with Bland-Altman plots showing acceptable agreement for ML but not TP.

Conclusions:

• Standardizing McRae line (ML) tracing with the multiplanar reconstruction (MPR) method enhances data acquisition for cerebellar tonsil position.
• MPR offers improved accuracy in assessing ML, a key parameter in CM1 diagnosis.
• Further refinement may be needed to fully optimize TP measurement reliability.