Purpose: To determine the efficacy of gamma knife radiosurgery in the treatment of mesial temporal lobe epilepsy due to mesial temporal sclerosis.
Methods: Between November 1995 and May 1999, 14 patients underwent radiosurgical entorhinoamygdalohippocampectomy with a marginal dose of 18, 20, or 25 Gy to the 50% isodose following a standard preoperative epilepsy evaluation.
Results: One patient was classified as Engel Class Ib, three were Engel Class IIc, one was Engel Class IIIa, and two were Engel Class IVb in a subgroup of seven patients who were unoperated 2 years prior to the last visit and at least 8 years after irradiation (average 116 months). The insufficient effect of irradiation led us to perform epilepsy surgery on another seven patients an average of 63.5 months after radiosurgery. The average follow-up period was 43.5 months after the operation. Four patients are seizure-free; one is Engel Class IIb and one is Engel Class IId. One patient cannot be classified due to the short period of follow-up. The frequency of seizures tended to rise after irradiation in some patients. Collateral edema was observed in nine patients, which started earlier and was more frequent in those irradiated with higher doses. It had a marked expansive character in three cases and clinical signs of intracranial hypertension were present in three cases. We found partial upper lateral quadrant anopia as a permanent side effect in two patients. Repeated psychotic episodes (two patients) and status epilepticus (two patients) were also seen after treatment. No significant memory changes occurred in the group as a whole.
Discussion: Radiosurgery with 25, 20, or 18-Gy marginal dose levels did not lead to seizure control in our patient series, although subsequent epilepsy surgery could stop seizures. Higher doses were associated with the risk of brain edema, intracranial hypertension, and a temporary increase in seizure frequency.