Delayed complication after Gamma Knife surgery for mesial temporal lobe epilepsy

Clinical article

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Despite the controversy over the clinical significance of Gamma Knife surgery (GKS) for refractory mesial temporal lobe epilepsy (MTLE), the modality has attracted attention because it is less invasive than resection. The authors report long-term outcomes for 7 patients, focusing in particular on the long-term complications.


Between 1996 and 1999, 7 patients with MTLE underwent GKS. The 50% marginal dose covering the medial temporal structures was 18 Gy in 2 patients and 25 Gy in the remaining 5 patients.


High-dose treatment abolished the seizures in 2 patients and significantly reduced them in 2 others. One patient in this group was lost to follow-up. However, 2 patients presented with symptomatic radiation necrosis (SRN) necessitating resection after 5 and 10 years. One patient who did not need necrotomy continued to show radiation necrosis on MRI after 10 years. One patient died of drowning while swimming in the sea 1 year after GKS, before seizures had disappeared completely.


High-dose treatment resulted in sufficient seizure control but carried a significant risk of SRN after several years. Excessive target volume was considered as a reason for delayed necrosis. Drawbacks such as a delay in seizure control and the risk of SRN should be considered when the clinical significance of this treatment is evaluated.

Abbreviations used in this paper:AVM = arteriovenous malformation; CPS = complex partial seizure; GKS = Gamma Knife surgery; MTLE = mesial temporal lobe epilepsy; SRN = symptomatic radiation necrosis.

Article Information

Address correspondence to: Kenichi Usami, M.D., Department of Neurosurgery, Faculty of Medicine, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8655, Japan. email:

Please include this information when citing this paper: published online March 23, 2012; DOI: 10.3171/2012.2.JNS111296.

© AANS, except where prohibited by US copyright law.



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    Dose planning for Cases 3 (A), 4 (B), and 5 (C). The 50% isodose line (white line) covers the amygdala, hippocampal head, body, parahippocampal gyrus, and entorhinal cortex.

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    Case 3. Magnetic resonance images. Coronal FLAIR (A) and axial Gd-enhanced (B) images obtained 10 months after GKS showing small areas of edema in the temporal lobe and a Gd-enhanced lesion in the medial temporal lobe. Coronal T2-weighted (C) and axial Gd-enhanced (D) images obtained 5 years after GKS showing augmentation of necrosis in the medial temporal lobe and diffuse edema around the area of necrosis.

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    Case 4. Magnetic resonance images. Coronal T2-weighted (A) and axial T1-weighted (B) images obtained before GKS showing a cavernous malformation in the right mesial temporal lobe. Coronal T2-weighted (C) and Gd-enhanced (D) images obtained 8 years after GKS showing hydrocephalus, a small area of radiation necrosis, and edema in the temporal lobe. Coronal FLAIR (E) and Gd-enhanced (F) images obtained 10 years after GKS showing improvement in hydrocephalus but deterioration of radiation necrosis and edema.

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    Case 5. Magnetic resonance images. Gadolinium-enhanced (A and B), T2-weighted (C), and FLAIR (D) images obtained 10 years after GKS show that a Gd-enhanced lesion and surrounding edema in the temporal lobe remain and cyst formation is observed in the temporal lobe.


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