Disproportionate Mass Effect as a Conventional MRI Marker of High-Grade Glioma

IntroductionTumor size and mass effect are commonly considered together on conventional magnetic resonance imaging (MRI), although they may represent different aspects of glioma behavior.This study compared the association of absolute mass effect, size-normalized mass effect, and estimated tumor volume with histopathological grade. MethodsThis single-center cross-sectional study included 30 adults with histopathologically confirmed gliomas who underwent preoperative MRI.Ellipsoid tumor volume and equivalent tumor diameter were calculated from three orthogonal dimensions.Mass effect was defined as maximum linear displacement of midline structures in millimeters.A mass-effect index (MEI) was defined as mass effect divided by equivalent tumor diameter.The World Health Organization (WHO) grade 2 tumors were categorized as low grade and grades 3-4 as high grade.Group comparisons, grade-wise trends, receiver operating characteristic analysis, logistic regression, and leave-one-out cross-validation were performed. ResultsThe cohort included eight grade 2, seven grade 3, and 15 grade 4 tumors.Tumor volume did not differ between low-and high-grade groups (median: 34.9 vs 54.7 cm 3 ; p = 0.622).High-grade tumors demonstrated greater mass effect (7.54 vs 3.33 mm; p = 0.009) and MEI (0.149 vs 0.075; p = 0.024).Absolute mass effect had the highest observed area under the curve (AUC: 0.821), compared with 0.776 for the index and 0.563 for volume.Its volume-adjusted association was imprecise (OR: 4.32; 95% CI: 0.95-19.75). ConclusionGreater absolute and size-normalized mass effect was associated with high-grade histology.Absolute mass effect had the highest observed AUC, but an independent contribution beyond volume was not established.These exploratory findings and thresholds require external validation.