Gamma Knife Radiosurgery of Skull Base Meningiomas: Analysis of Long-Term Results

Jason P. Sheehan, PhD1

1Department of Neurosurgery, University of Virginia

Keywords: meningioma, gamma knife, skull base, outcome, radiosurgery

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     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, we evaluated the outcomes of skull base meningiomas treated with Gamma Knife radiosurgery (GKRS) both as an adjunct to microsurgery and as a primary treatment modality.
     There were 60 males and 230 females with a median age of 55 years (range 19-85). One hundred sixty one patients were treated with upfront radiosurgery, and 129 patients were treated following surgical resection.
     We performed a retrospective review of a prospectively compiled database detailing the outcomes of 290 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.  Factors predictive of new neurological deficit following GKRS were assessed via univariate and multivariate analysis, and Kaplan-Meier analysis and Cox multivariate regression analysis was used to assess factors predictive of tumor progression.
     Patients had meningiomas centered over the tentorium (35; 12%), cerebellopontine angle (43; 15%), petroclival region (28; 10%), petrous region (6; 2%), clivus (40; 14%), and parasellar (138; 48%). The median follow-up was 6.3 years (range 2-18 years). The mean pre-radiosurgery tumor volume was 6.6 cc. 251 patients (87%) displayed no change or decrease in tumor volume, and 39 (13%) displayed an increase in volume. Kaplan Meier analysis demonstrated radiographic progression free survival at 3, 5, and 10 years to be 99%, 95%, and 78% respectively. Pre-GKRS covariates associated with tumor progression include age great then 65 (p=0.001) and decreasing dose to the margin of the tumor (p=0.05). At last clinical follow-up, 263 patients (91%) demonstrated no change or improvement in their neurological condition and 27 patients deteriorated (9%). In multivariate analysis, the factors predictive of new or worsening symptoms were increasing follow up (p=0.01), decreasing maximum dose (p=0.019), tumor progression (p=0.001), and parasellar, clival, or petrous location versus cerebellopontine angle, petroclival or tentorial location (p=0.018).
     This was a retrospective study.
     GKRS offers a high rate of tumor control and neurological preservation in patients with skull base meningiomas. 
     More favorable outcomes were observed for those receiving an optimal radiosurgery dose and harboring tumors located in a cerebellopontine angle, petroclival or tentorial location.


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