Recent data suggest that Gamma Knife Radiosurgery can be used with acceptable safety and efficacy in patients with medial temporal lobe epilepsy and offers a potentially valuable modality to provide long-term seizure control in patients with a single temporal lobe seizure focus. This procedure may offer a way to treat patients effectively whom have a single, well-defined seizure focus and avoid the risks associated with a craniotomy.
Regis and colleagues reported the results of a collaborative study from three centers in Europe (1). Twenty-one patients were selected, whose pre-surgical evaluation revealed a mesial temporal lobe focus. Radiosurgery was performed in all 21 in place of anterior temporal lobectomy. The Leksell Gamma Knife® (Elekta Instruments, Inc., Atlanta, GA and Stockholm, Sweden) was used at all centers, and the target was the basal and lateral part of the amygdala, the anterior hippocampus (head and body), and the anterior parahippocampal gyrus. Of the 21 patients, 20 were available for follow-up at 2 years. The median seizure frequency was reduced from a baseline of 6.16 per month to 0.33 per month at the 2-year follow-up. At 2 years, 65% of the patients were free of seizures. Quality-of-life measures improved significantly for mental health and role functioning. Limits of the procedure include an initial period of increased seizures, and a delay until seizures are reduced or fully controlled. It should be noted that all patients experienced a transient increase in their seizures before there was a decrease.
Side effects included transient increase in seizures, symptoms of radiation-induced tissue changes, and visual field deficits. (this repeats a statement in the preceding paragraph). These were usually auras, although 1 patient experienced a cluster of seizures with Todd’s paralysis and required hospitalization 12 months after the gamma knife surgery. The most significant but transient MRI changes of radiation-induced tissue changes occurred around 12 months after treatment. This corresponded to the time when 5 of 20 patients developed headache, nausea, vomiting, depression, and dizziness. Corticosteroids were used to treat the disorder in 62% of patients. Three patients required hospitalization for the severity of these symptoms and parenteral administration of corticosteroids. Visual fields revealed new quadrantic deficits in 10 patients (attributed to injury to the optic radiation) and 1 patient with a hemianopia (attributed to injury to the optic tract). There were no neuropsychological deficits, including verbal memory or naming impairment.
The success rate suggested by this study is similar to that reported following standard temporal lobectomy. However, the risks associated with traditional temporal lobe epilepsy surgery are low (less than 1% mortality and under 3% morbidity), so one must question why gamma knife radiosurgery, with its associated side effects, would be necessary as an alternative to open surgery. Furthermore, whereas the long-term benefits of temporal lobectomy are well-documented, the late success of gamma knife in this condition is unknown. Future studies will address late effects, as well as the utility of this approach in patients with refractory epilepsy associated with other brain lesions, such as cortical dysplasia and hypothalamic hamartoma.
Reviewed and revised November 2004 by Howard Weiner, MD, New York University.
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