Clinical and pathological impact of an optimal assessment of brain invasion for grade 2 meningioma diagnosis: lessons from a series of 291 cases.

Brain invasion has not been recognized as a standalone criterion for atypical meningioma by the WHO classification until 2016. Since the 2007 edition suggested that meningiomas harboring brain invasion could be classified as grade 2, brain invasion study was progressively strengthened in our center, based on a strong collaboration between neurosurgeons and neuropathologists regarding sample orientation and examination. Practice changes were considered homogeneous enough in 2011. The aim of the present study was to evaluate the impact of gross practice change on the clinical and pathological characteristics of intracranial meningiomas classified as grade 2.The characteristics of consecutive patients with a grade 2 meningioma surgically managed before (1998-2005, n = 125, group A) and after (2011-2014, n = 166, group B) practices changed were retrospectively reviewed.Sociodemographical and clinical parameters were comparable in groups A and B, and the median age was 62 years in both groups (p = 0.18). The 5-year recurrence rates (23.2% vs 29.5%, p = 0.23) were similar. In group A, brain invasion was present in 48/125 (38.4%) cases and was more frequent than in group B (14/166, 8.4%, p < 0.001). In group A, 33 (26.4%) meningiomas were classified as grade 2 solely based on brain invasion (group ASBI), and 92 harbored other grade 2 criteria (group AOCA). Group ASBI meningiomas had a similar median progression-free survival compared to groups AOCA (68 vs 80 months, p = 0.24) and to AOCA and B pooled together (n = 258, 68 vs 90 months, p = 0.42).An accurate assessment of brain invasion is mandatory as brain invasion is a strong predictor of meningioma progression.