Differential tumor progression patterns in skull base versus non-skull base meningiomas: A critical analysis from a long-term follow-up study and review of literature.

BACKGROUND: To analyze the differences in tumor progression patterns and histopathologic characteristics between skull base meningiomas (SBMs) and non-skull base meningiomas (NSBMs). METHODS: Retrospective data of 382 patients with SBMs and 200 patients with NSBMs who underwent primary microsurgical resection between January 1995 and December 2016 were analyzed. Data related to clinical history, neuroimaging, surgical technique, and follow-up were reviewed. A separate prospective cohort of 78 meningiomas operated on from June 2016 to July 2017 was analyzed (World Health Organization [WHO] grade and Ki-67 proliferation index) for biologic comparison. RESULTS: Skull base location, WHO grade II tumor, and subtotal resection were independent predictors of unfavorable outcome. The overall tumor progression rate in the SBM group (33%) was higher than in the NSBM group (19.7%) (P = 0.006) (mean follow-up period, 51 months). The 3-year, 5-year, and 10-year progression-free survival (PFS) was 78%, 60%, and 45% in the SBM group, whereas it was 90%, 80%, and 53% in the NSBM group, respectively. Interestingly, there was no difference in the median PFS after 10 years of follow-up (SBMs 210 months vs. NSBM 212 months, P = 0.93). In the prospective cohort of 78 meningiomas, there was no statistically significant difference in the proportion of WHO grade I tumors and in the mean Ki-67 index of WHO grade I meningiomas between the 2 groups. CONCLUSION: There is a divergent tumor progression pattern for surgically treated SBMs vis-a-vis NSBMs. Differences in tumor biology and the proportion of Simpson grade I resections are likely attributable factors.