Gamma Knife Surgery for the Management of Intrinsic Brainstem Tumors and Vascular Lesions

David Hung-Chi Pan1

1Taipei, Taiwan

Keywords: brain tumor, gamma knife, vascular malformation, brain stem, outcome

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     Brainstem lesions are suitable for stereotactic radiosurgery.
We present a retrospective study of 111 patients with intrinsic brainstem lesions treated by Gamma Knife surgery (GKS) between 1993-2009.
     These lesions include 26 gliomas, 49 cavernous malformations, 20 AVMs and 16 metastatic tumors. Criteria of patients’ selection for GKS are based on thorough clinical and imaging studies to show a well-demarcated lesion in the brain stem which is difficult to treat with conventional surgery or radiotherapy. 
     During GKS, varied radiosurgical doses to the lesion margin were prescribed based on the lesion size and nature: AVMs 15-22Gy, gliomas and cavernous malformations 10.5-12Gy, and metastasis 11.5-20Gy. After radiosurgery, all patients underwent regular imaging follow-ups every 2-6 months to assess treatment results. For AVMs, a final angiogram was performed 2-4 years post-treatment to verify complete obliteration.
     In 20 AVMs, 15 have shown angiographically confirmed complete obliteration. The obliteration rate was 75%. Complications included 1 (5%) radiation-induced edema, 1 (5%) mild rebleeding and 2 (10%) focal infarction with hemiparesis. There was no mortality. In 49 cavernous malformations, the annual hemorrhagic rate significantly reduced from 28.2% of the pre-GKS status to 3.33% within 2 years post-GKS, and further reduced to 1.74% over 2 years after radiosurgery. In 26 gliomas, the follow-up time ranged from 6-181 months (median 37 months). Post-GKS MRI revealed tumor regression in 8 (30%), stable in 9 (35%), and enlarged in 9 (35%). Five (19%) glioma patients died due to tumor progression, others (81%) were clinically stable after GKS. In 16 patients with metastatic tumors, a prolonged survival over 12 months with initial shrinkage of tumors was observed in 10 patients.
     This was a retrospective study.
     Our data suggest that GKS is effective for the treatment of selected brainstem neoplasm or vascular lesions with acceptably low risks. 
     Careful selection of patients before treatment is necessary.


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D. Pan ()