Gamma Knife surgery for skull base meningiomas
Authors: Starke Robert M. , Williams Brian J. , Hiles Claire , Nguyen James H. , Elsharkawy Mohamed Y. , Sheehan Jason P. 
Published: December 2011

Object
Skull base meningiomas are challenging tumors owing in part to their close proximity to important neurovascular structures. Complete microsurgical resection can be associated with significant morbidity, and recurrence rates are not inconsequential. In this study, the authors evaluate the outcomes of skull base meningiomas treated with Gamma Knife surgery (GKS) both as an adjunct to microsurgery and as a primary treatment modality.

Methods
The authors performed a retrospective review of a prospectively compiled database detailing the outcomes in 255 patients with skull base meningiomas treated at the University of Virginia from 1989 to 2006. All patients had a minimum follow-up of 24 months. The group comprised 54 male and 201 female patients, with a median age of 55 years (range 19–85 years). One hundred nine patients were treated with upfront radiosurgery, and 146 patients were treated with GKS following resection. Patients were assessed clinically and radiographically at routine intervals following GKS. Factors predictive of new neurological deficit following GKS were assessed via univariate and multivariate analysis, and Kaplan-Meier analysis and Cox multivariate regression analysis were used to assess factors predictive of tumor progression.

Results
Meningiomas were centered over the cerebellopontine angle in 43 patients (17%), the clivus in 40 (16%), the petroclival region in 28 (11%), the petrous region in 6 (2%), and the parasellar region in 138 (54%). The median duration of follow-up was 6.5 years (range 2–18 years). The mean preradiosurgery tumor volume was 5.0 cm3 (range 0.3–54.8 cm3).
At most recent follow-up, 220 patients (86%) displayed either no change or a decrease in tumor volume, and 35 (14%) displayed an increase in volume. Actuarial progression-free survival at 3, 5, and 10 years was 99%, 96%, and 79%, respectively. In Cox multivariate analysis, pre-GKS covariates associated with tumor progression included age greater then 65 years (HR 3.41, 95% CI 1.63–7.13, p = 0.001) and decreasing dose to tumor margin (HR 0.90, 95% CI 0.80–1.00, p = 0.05).
At most recent clinical follow-up, 230 patients (90%) demonstrated no change or improvement in their neurological condition and the condition of 25 patients had deteriorated (10%). In multivariate analysis, the factors predictive of new or worsening symptoms were increasing duration of follow-up (OR 1.01, 95% CI 1.00–1.02, p = 0.015), tumor progression (OR 2.91, 95% CI 1.60–5.31, p < 0.001), decreasing maximum dose (OR 0.90, 95% CI 0.84–0.97, p = 0.007), and petrous or clival location versus parasellar, petroclival, and cerebellopontine angle location (OR 3.47, 95% CI 1.23–9.74, p = 0.018).

Conclusions
Stereotactic radiosurgery offers a high rate of tumor control and neurological preservation in patients with skull base meningiomas. After radiosurgery, better outcomes were observed for those receiving an optimal radiosurgery dose and harboring tumors located in a cerebellopontine angle, parasellar, or petroclival location.