A Single-Institution Review of 84 WHO II Meningiomas, 38 Located in the Skull Base, Continues to Support Surgery as the Primary Treatment Modality

Background WHO Grade II meningiomas account for 10 to 15% of all meningiomas. These tumors have a 5-year recurrence rates between 30 and 50%, and 5-year survival rates as low as 50%. Surgery is the primary treatment for these neoplasms, while the use of various adjuvant treatments remains debated. Continuing to study patient outcomes in relation to histological features, and clinical course, will help clinicians and surgeons makes informed, evidence-based treatment plans to optimize care for patients with WHO Grade II meningiomas.

Methods We considered histological subtype, histological features, recurrence time, overall survival, embolization, tumor location, and course of treatment as variables in our study. Kaplan–Meier, Spearman's rank correlations, and cox regression hazard ratio were used to analyze the data.

Results In this study, we retrospectively analyzed 84 Grade II meningiomas that met the 2017 WHO criteria, 38 of which were located in the skull base. Twelve patients had a histological Grade I with brain invasion, 59 were atypical, 8 were clear cell, and 5 were chordoid. 51.2% of patients were recurrence free at 5 years, and 77.4% were alive at 5 years. Location in the skull base was associated with lower recurrence (p = 0.037), but not improved survival (p = 0.56). Gross total resection was also associated with lower recurrence (p < 0.001), and much lower recurrence in skull based tumors (p < 0.00001). Gross total resection was insignificantly associated with improved survival (p = 0.067), similar results were achieved in skull base tumors (p = 0.12). Radiation treatment, including gamma knife, had no impact on recurrence or survival, in both subtotal and gross total resections. Mitoses and MIB index were not significantly correlated with recurrence (p = 0.064 and 0.864, respectively). De Novo tumors were insignificantly associated with improved survival (p = 0.062) and recurrence (p = 0.15); while brain invasion, chordoid, and clear cell had no impact. No histological subtype or feature was associated with survival in skull base tumors, while brain invasion resulted in higher recurrence (p = 0.042).

Conclusion Based on our cohort of tumors, gross total resection is the best prognostic indicator of patient outcome, regardless of location, for patients with Grade II meningiomas. In contrast to more recent reports supporting the use of radiation therapies, our cohort showed no improvement in outcomes regardless of gross total resection with adjuvant radiation. This supports surgery as the most beneficial therapy. However, additional considerations for adjuvant therapy may be warranted for skull base Grade II meningiomas with brain invasion due to higher recurrence.