Higher brain function changes after selective amygdala-hippocampai radiosurgery in medial temporal lobe epilepsy : Relationship between neuropsychological findings and functional MRI

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The use of radiosurgery in the treatment of intractable temporal lobe epilepsy has emerged as a non-invasive alternative to resection. We report the results of gamma knife radiosurgery in seven patients, two males and five females, with medically refractory medial temporal lobe. The patients had received pre- and post-surgical evaluation that included video-EEG, MRI, ictal SPECT, octal PET, functional MRI, and neuropsychological tests. In first two cases, we treated with a marginal dose of 18 Gy to the 50 % isodose line, which completely covered the amygdala hippocampal head and body, and parahippocampal gyrus. In both cases, MR imaging revealed no remarkable change of findings in medial temporal lobe structure after radiosurgery and this procedure failed to control seizures. Both patients became seizure free after undergoing anterior temporal lobectomy 30 and 16 months, respectively, after radiosurgery. Histological examination of the resected specimen revealed hippocampal sclerosis, reactive astrocytes, and small or no necrotic focus. These findings suggests that low-dose radiosurgery failed to achieve sufficient anti-epileptic effects. In addition, five patients were treated with high dose, a marginal dose of 25 Gy to the 50% isodose line, radiosurgery. All patients continued to thave seizures with the same frequency after gamma knife radiosurgery. MR imaging in these patients revealed marked edema in the medial temporal lobe. It is difficult to draw any definite conclusion based on our limited experiencee with seven cases of failed gamma knife radiosurgery. To achieve seizure cessation by using radiosurgery, it may be necessary to destroy the medial temporal structures completely, as in a resection.