Gamma Knife radiosurgery for skull base meningioma: long-term results of low-dose treatment

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In this study, the authors evaluate the long-term results after Gamma Knife radiosurgery of cranial base meningiomas. This study is a follow-up to their previously published report on the early results.


Between January 1994 and December 2001, the authors treated benign cranial base meningiomas in 108 patients using low-dose Gamma Knife radiosurgery. The tumor volumes ranged from 1.7 to 55.3 cm3 (median 8.1 cm3), and the radiosurgery doses ranged from 8 to 12 Gy (median 12 Gy) to the tumor margin.


The mean duration of follow-up was 86.1 months (range 20–144 months). Tumor volume decreased in 50 patients (46%), remained stable in 51 patients (47%), and increased (local failure) in 7 patients (6%). Eleven patients experienced tumor recurrence outside the treatment field. Among these patients, marginal failure was seen in 5 and distant recurrence was seen in 6. Seven patients were thought to have malignant transformation based on histological or radiological characteristics of the lesion. The actuarial progression-free survival rate, including malignant transformation and outside recurrence, was 93% at 5 years and 83% at 10 years. Neurological status improved in 16 patients (15%). Permanent radiation injury occurred in 7 patients (6%).


Gamma Knife radiosurgery is a safe and effective treatment for cranial base meningiomas as demonstrated with a long-term follow-up period of > 7 years. Surgeons must be aware of the possibility of treatment failure, defined as local failure, marginal failure, and malignant transformation; however, this may be the natural course of meningiomas and not related to radiosurgery.

Abbreviation used in this paper: GKS = Gamma Knife radiosurgery.

Article Information

Address correspondence to: Yoshiyasu Iwai, M.D., Ph.D., Department of Neurosurgery, Osaka City General Hospital, 2-13-22, Miyakojima-hondhohri, Miyakojima-ku, Osaka, 534-0021, Japan. email:

© AANS, except where prohibited by US copyright law.



  • View in gallery

    A: Axial Gd-enhanced MR images obtained from a 38-year-old woman, revealing right petrocavernous meningioma causing progressive facial numbness. The lesion, with a volume of 13.1 cm3, was treated with 10 Gy to the tumor margin. B and C: Follow-up axial MR images obtained in the same patient 5 and 10 years after radiosurgery. The tumor decreased in size.

  • View in gallery

    Flow diagram of tumor recurrence pattern in the patients who underwent GKS for skull base meningiomas.

  • View in gallery

    Kaplan–Meier curve showing progression-free survival rates in 108 patients who underwent GKS for skull base meningiomas.


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