Conventional MRI Features Associated with Histopathological Markers of Biological Aggressiveness in Atypical Meningiomas

Background: Atypical meningiomas (CNS WHO grade 2) are biologically heterogeneous, and reliable preoperative imaging correlates of tumor biology remain incompletely defined. This study investigated associations between routinely acquired conventional MRI features and histopathological markers of biological aggressiveness within this tumor grade. Methods: We retrospectively analyzed 90 consecutive patients who underwent surgical resection for histologically defined atypical meningiomas between January 2016 and March 2025. Histopathological specimens were re-reviewed according to the 2021 WHO Classification. Conventional MRI features and apparent diffusion coefficient (ADC) values were evaluated in relation to the Ki-67 labeling index (LI), mitotic count, hypercellularity, spontaneous necrosis, pathological brain invasion, and progesterone receptor expression. Ki-67 LI and ADC were analyzed primarily as continuous variables. A literature-informed Ki-67 threshold of ≥8% was used for secondary categorical analysis, with ≥4% and ≥10% retained as sensitivity analyses. Benjamini–Hochberg false-discovery-rate correction was applied to exploratory categorical comparisons. Results: The median age was 59 years, and 56 patients (62.2%) were female. The median Ki-67 LI was 10% (IQR, 5–15), and the median ADC was 0.78 × 10−3 mm2/s (IQR, 0.73–0.88). ADC showed a weak inverse correlation with Ki-67 LI (ρ = −0.255; 95% CI, −0.44 to −0.05; p = 0.015) but was not significantly correlated with mitotic count (ρ = −0.124; p = 0.244). In the adjusted continuous model, the association between ADC and Ki-67 was not statistically significant (Ki-67 ratio per 0.1 × 10−3 mm2/s increase in ADC, 0.95; 95% CI, 0.87–1.04; p = 0.264). Similarly, the secondary analysis using Ki-67 ≥ 8% yielded an imprecise association with ADC (OR, 0.865; 95% CI, 0.713–1.002; p = 0.054). Among 96 exploratory categorical comparisons, only the association between radiological and pathological brain invasion remained significant after false-discovery-rate correction (q = 0.003). Conclusions: Conventional MRI features showed weak and largely exploratory associations with histopathological markers of biological aggressiveness in histologically defined atypical meningiomas. Lower ADC was weakly correlated with higher Ki-67 LI, but this association was not robust after adjustment. Radiological brain invasion was strongly associated with pathological brain invasion. These findings should be considered hypothesis-generating and require prospective multicenter validation incorporating standardized imaging, molecular profiling, and clinically relevant outcomes before clinical application.