Mitotic Count, Brain Invasion, and Location Are Independent Predictors of Recurrence-free Survival in Primary Atypical and Malignant Meningiomas: a Study of 86 Patients

Background: Since precise diagnostic criteria for atypical and malignant meningiomas (AMMs) were provided for the first time in the 2000 World Health Organization (WHO) criteria, there is only sparse information about possible prognostic factors in the group of AMMs.

Objective: To evaluate the prognostic significance of various histological and clinical parameters in AMMs, with an emphasis on location, mitotic count, brain invasion, and Ki67 labeling index.

Methods: We analyzed 86 primary AMMs, 76 of which were atypical and 10 of which were malignant, diagnosed according to the 2000 WHO classification. Multivariate Cox survival analyses were performed.

Results: High mitotic count, brain invasion, and the parasagittal-falcine location of the tumor were significantly associated with decreased recurrence-free survival in multivariate analysis. Brain invasion was present in 25 of 37 cases in which brain tissue was identified in the tumor specimens. When brain invasion was not included in the analysis because of the limited number of cases in which it could be assessed, high mitotic count, Ki67 index >4%, the presence of macronucleoli, and parasagittal-falcine location were significant predictors of shorter recurrence-free survival.

Conclusion: AMMs, as defined by 2000 WHO, are biologically heterogeneous. Recurrence-free survival can be further stratified by location and histological parameters, especially mitotic count, brain invasion, and Ki67 labeling index. Not only brain invasion, but also the presence or absence of brain tissue in surgical specimens should be reported, because the absence of brain invasion, when brain tissue is identified, provides very important positive prognostic information.