To investigate clinicopathological predictors of tumor recurrence and radio-resistance in atypical meningiomas. 

Meningiomas are the most common tumors in the central nervous system, with variable recurrence rates depending on WHO grading. Atypical (WHO grade II) meningioma has a higher recurrence rate than benign (WHO grade I) meningioma. The efficacy of adjuvant radiotherapy (RT) to reduce tumor reoccurrence has been questioned.

181 cases at St. Michaels Hospital with a diagnosis of atypical meningioma (AM) who underwent surgical resection between 1995 and 2015 were retrospectively reviewed. All included cases had a minimum follow-up of 4 years. Patient and tumor characteristics such as location, neuropathological diagnosis, resection extent, RT and reoccurrence were recorded. Resection extent was defined by Simpson Grading Scale as either Gross Total (GTR) or Subtotal (STR) resection. Cox univariate regression and Kaplan-Meier survival analysis were employed to identify risk factors for recurrence and radio-resistance. 

In our cohort, the combination of necrosis and brain invasion was the only pathological predictor significantly associated with an increased reoccurrence risk (HR= 4.560, P=0.001); necrosis alone did not reach significance (HR=1.898, P=0.145). Similarly, combined necrosis and brain invasion had the worst cumulative survival relative to any other pathological predictor, including necrosis (P=0.001). This trend was maintained after GTR (P=0.001), whereas necrosis alone and combined necrosis and brain invasion behaved similarly after STR(P=0.001). 

RT was administered on clinical criteria. Examination of the factors associated with administered RT identified combined necrosis and brain invasion (HR=3.088, p=0.034) and STR (HR= 3.143, P=0.001). RT was associated with worse survival (P=0.001), especially after GTR (P=0.001). Unlike high mitotic count (P=0.961), necrosis alone (P=0.002) but specially combined necrosis and brain invasion (P=0.001) magnified the apparent deleterious effect of RT.

Combined necrosis and brain invasion is a strong predictor of tumor recurrence and radio-resistance in AM, regardless of resection type or RT.