Posterior parasagittal meningiomas display aggressive features independent of size: a multicenter analysis.

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Abstract Purpose While meningioma size is known to correlate with higher histological grade, tumor behavior can vary by anatomical location, suggesting that some meningiomas may exhibit aggressive features early and independent of size. We hypothesized that posterior parasagittal meningiomas possess unique growth characteristics and tested this hypothesis using a retrospective analysis of two independent cohorts. Methods Cohort-A (n = 316) included 123 WHO-grade 2 (GR2) and 193 age and location matched WHO-grade 1 (GR1) meningiomas. Twelve radiological features as well as the histological subtypes, histological grading features and 1p status was evaluated. A volume index (Vi), defined as the GR2/GR1 tumor volume ratio, was calculated across different anatomical locations. Findings were validated in Cohort-B (n = 477), which also included NF2-driven and non-NF2-driven molecular subsets. Results Tumor volume correlated strongly with GR2 status (p = 3.5 × 10− 6) and histopathological markers of major grading criteria including mitotic count (p < 0.001), brain invasion (p < 0.05), and minor grading criteria including hypercellularity (p < 0.001), necrosis (p < 0.001) along with increased Ki67 index (p < 0.01). Anatomically, the non-skull base posterior midline (NSB-POST-M) meningiomas had the lowest Vi in both cohorts and the NF2-driven subset indicating that these tumors exhibit aggressive features even at smaller sizes. The NSB-POST-M location had the highest proportion of GR2 cases, mean Ki67 index, and incidence of chromosome 1p loss. Conclusions While larger meningiomas are generally more aggressive, posterior parasagittal meningiomas display aggressive biology regardless of size. These findings suggest that anatomical location should be incorporated into risk stratification and management decisions.