Task: Question Answering
Input (English): Context: The rarity and the inconsistent criteria for defining atypical meningioma prior to the WHO 2007 classification made its management and prognostic factors poorly understood. Only few articles have addressed the survival rates of WHO-classified atypical meningiomas. The small number or the disproportionate representation of irradiated patients was a weakness for these articles. This study evaluated whether the extent of surgery and receiving adjuvant radiotherapy after an initial operation along with other patient characteristics influenced the recurrence and survival rates of atypical meningiomas. The clinical and surgical notes of the 79 patients with grade II atypical meningioma treated at our center over 13 years were retrospectively evaluated. The histology grading was consistent with WHO 2007 classification. The Simpson grading system was used to assess the extent of surgical resection. Kaplan Meier analysis, Cox multivariate regression analysis, and the Log-rank test were conducted using STATA® statistical package. The average age at the time of initial operation was 58 years, and 54 % were males. The mean follow-up period was 50 months. In Cox multivariate analysis, only Simpson grading was predictive of recurrence (hazard ratio = 2.22 / 1 increase in Simpson grade. p=0.003). Simpson grade I patients had a relapse-free survival rate of 97 and 74 % at one and five years, respectively, compared with 88 and 32 % in the subtotal resection group (Simpson grades II to IV). There was no statistically significant correlation between recurrence and subjecting patients to postoperative radiotherapy. Apart from Simpson grade I patients, there was a general trend for worse outcome in irradiated patients. The most important prognostic factor in determining recurrence was Simpson grading. There was no statistically significant impact of adjuvant radiotherapy on the recurrence of atypical meningiomas. Meta-analysis for the existing literature is needed. 
 Question: Simpson grading is used to describe resection of which brain tumor?
Output (English): meningioma