Stereotactic radiosurgery may be effective in the treatment of idiopathic epilepsy: report on the methods and results in a series of eleven cases.

Between 1982 and 1991, 11 patients (4 male, 7 female) ranging in age from 16 to 42 years who had been diagnosed with idiopathic focal epilepsy resistant to medication, were treated with stereotactic radiosurgery. The preoperative symptomatic period was 3-24 years. The process of localizing epileptic focus was based on chronic electrocorticography with flexible electrodes introduced into the subarachnoid space through single burr holes, and left in place during a maximum of 7 days until a clinical seizure was recorded. In most cases the procedure had to be repeated until localization was clear. This process was aided by a computer-assisted automatic analysis procedure. Final confirmation of focus location was done with depth electrode recording in most cases. Stereotactic radiosurgery was performed with a 60Co gamma source using 10 mm collimators, except in two cases in which a betatron was used. The estimated dose was 10-20 Gy at the isocenter. Four of the 11 patients (36%) were medication- and seizure-free after a mean follow-up of 102.5 months. Five patients (45%) presented a reduction of seizures of 98, 89, 86, 75 and 75%, respectively. Two patients did not respond to treatment. Seizure reduction began after a delay period of 2-12 months except in 2 patients and in most cases seizure rate decreased progressively during several months (range: 3-48) postoperatively until stabilization. No complications related to irradiation were recorded. Doses effective for epilepsy are much lower than those for producing cerebral lesions, so the mechanism is not destruction of the focus of the pathways spreading the epileptic activity.(ABSTRACT TRUNCATED AT 250 WORDS)