Objective: The current classification of meningioma is based on the mitotic count, brain invasion and atypical histological changes. We re-evaluated the cases of meningioma to make accurate grading and to investigate the effects of morphological parameters and their relationship with each other. We discussed the counting method of mitotic activity. We tried to develop a novel method to determine the most accurate grade.
Materials and Methods: In this study, three hundred nine cases of meningioma were re-evaluated. The number of mitosis in 10 consecutive high-power fields, as well as the total number of mitosis in 1 cm2 area, was found for all cases. Receiver Operating Characteristics curve analysis was performed on the mitotic counts of 304 cases (grade I and II) in both 10 consecutive high-power fields and 1 cm2 for predicting the grade.
Results: In Receiver Operating Characteristics curve analysis, the number of mitoses determining grade II with 99% specificity and 84.4% sensitivity in 1 cm2 was 7 or more. Receiver Operating Characteristics curve analysis for the mitotic count in 10 consecutive high-power fields when the number of mitosis 4 or more, the sensitivity was 84.4%, and it was 100% specific for grade II.
Conclusion: The major cause of the grade change was the number of mitotic activities. We recommend that the mitotic activity count in a large area. Especially, if there is 7 or more mitosis in 1 cm2, the case is to be high-grade. On the other hand, the presence of 1 or more mitosis in 42 high-power fields supports that this case is more likely to be grade II.