Interobserver Variability in Mitotic Count for Meningioma Grading: How Can We Reduce It?

Aim: To evaluate the interobserver variability in determining the number of mitoses in 10 high-power field (HPF) and thus the tumor grade, and to investigate how to reduce grade discordance between the observers and the most useful method to identify the patients who would receive an additional treatment.

Material And Methods: Two hundred and seventy cases with meningioma were re-evaluated by three experienced pathologists and five senior residents. They determined the number of mitotic figures in 10 HPF in each slide. Re-evaluation of the cases, which were found of different grades from the reference observers was requested by full scan method. Statistical analysis was performed by using SPSS V23.0.

Results: A moderate agreement was found between the observers and the reference observer. After the evaluation of mitotic activity with the full scan method, the mean numbers of mitoses found by the observers in 10 HPF were increased. In the first evaluation, 4?6 cases were defined as Grade II by the observers. Whereas, 23?27 cases were defined as Grade II after the full scan method.

Conclusion: If there are less than 16 mitotic figures throughout the slide, it is more difficult to find the 10 HPF including 4 or more mitosis. Interobserver variability in mitotic figure counting can be reduced by full scan method, and examining the hematoxylin and eosin stained slides by the full scan method helps us to determine the true histologic grade of meningiomas in most cases, who would receive an additional treatment.