Gamma Knife Radiosurgery for Atypical or Anaplastic Meningioma ? Efficacy and Pathological Findings

Keywords: meningioma, malignant meningioma, brain tumor, gamma knife, neuropathology

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     To analyze the efficacy of Gamma Knife Radiosurgery (GKS) for malignant type meningioma (WHO grade II or grade III) focusing on pathological findings after GKS.
       Among 85 patients of meningiomas treated by GKS in Koyo Hospital from 1995 to 2008, 14 patients were diagnosed as an atypical or anaplastic meningioma before GKS. We can follow all 14 clinical courses for 17 lesions at least 1 year after GKS. Three patients were treated for a distant lesion at a different time. Their pathology revealed as a grade II (atypical) in 7 patients and grade III (anaplastic) in 7. The average of patients’ age is 60.3 and the number of male is 8 (57.1%). .
     The average of marginal dose at 17 lesions is 18.1 (6.0-23.0) Gy and maximum dose is 35.4 (12.0-46.0) Gy. Tumor volume is calculated 7.8ml (0.4-28.5) at average
     In 17 lesions, 6 lesions were followed with no recurrence for 28.0 months (average) after GKS (Good-control group). The other 11 lesions resulted in 7 recurrent tumors and 4 patients’ death (Poor-control group). Good-control tumor was treated 20.2/40.3 (marginal/maximum) Gy at dose for 3.1ml volume at the average, while poor-control was 16.9/32.6Gy, 10.3ml respectively. Smaller (p=0.056) and higher maximum dose (p=0.036) at GKS have a chance to a good tumor control. Overall, in 14 patients, only 2 patients were followed satisfactorily with no-recurrence after GKS. Five patients (6 lesions) suffered from the resection of re-growth tumor in 13.5 months (median) after GKS. Five pathological findings were tumor recurrence (marginal dose: 17.4Gy, average) and one was mainly tumor necrosis for which we had treated in 23Gy at a marginal dose. 
     This is a retrospective study.
     GKS for malignant type meningioma could have possibility to avoid tumor recurrence with smaller volume (less than 3.0ml) and higher dose (over 40Gy at maximum dose).
     A high-dose irradiation may cause tumor necrosis as well as tumor control relatively earlier after GKS.


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