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Response: Gamma Knife Surgery in Mesial Temporal Lobe Epilepsy

To the Editor: We read with great interest the article by J. Regis and colleagues (1) on Gamma Knife Surgery (GKS) for Temporal Lobe Epilepsy (TLE), published recently in Epilepsia. Several issues, however, need some clarification. The authors reported on a total of 20 patients with refractory epilepsy of whom 13 of 20 achieved Engel I and six of 20, Engel II status after GKS after a follow-up time of 2 years, which translated into a seizure-free survival rate of 65%. It remains unclear why such a striking difference between the three participating centers (77% vs. 50% vs. 33% seizure-free survival rate) was encountered for the major end point seizure-free survival. Is this a reflection of the quality of radiosurgery or patient selection? It may be emphasized that a recent report from the Cleveland Clinic with obviously the same radiosurgery protocol in TLE brought about devastating results, with tow of five patients dying between 1 month and 1 year after GKS, and the remainder achieving no reduction in seizure frequency at all (2). Of more concernat least from our point of view-seems the fact that almost 50% (nine of 20) of the patients experienced permanent radiation-related sequelae (namely, visual field defects including quadrantanopsia and hemianopsia) and additionally in 62% of the patients, a prolonged use of corticosteroids due to clinical symptoms was needed. To have the opportunity to reproduce these results, it would seem most desirable to learn more on the exact delineation/definition of the target volume of radiosurgery, the coverage, and other indices (homogeneity, conformity index) according to the RTOG radiosurgery quality assurance guidelines (3). As compared with the excellent results given by groups after resective epilepsy surgery (4–6), the outcome of GKS in patients that were primarily amenable for surgery really do not support the use of radiosurgery in all cases of mesial temporal lobe epilepsies. In addition, no neuropathologic examination can be performed. In our series of highly selected patients not amenable to open neurosurgery, we have chosen a different approach using radiosurgery with a fractionated regimen. No cases of permanent neurologic deficits were observed (mean observation time, 5 years), and the reduction in seizure frequency and length was remarkable (7,8). Further longterm follow-up observations are necessary and will be performed. Gerhard G. Grabenbauer Antje Ernst-Stecken Oliver Ganslandt Hermann Stefan Departments of Radiation Therapy Neurosurgery, Epileptology and Novalis Shaped Beam Surgery Center University of Erlangen Erlangen, Germany