Objective: Radiosurgical ablation of the mesial temporal lobe structures can be used in the treatment of intractable temporal lobe epilepsy associated with mesial temporal sclerosis. In this study, we analyzed the magnetic resonance imaging (MRI) and spectroscopic changes that follow the treatment and report the clinical sequelae of the procedure.
Methods: Eight patients (five men and three women; age, 38 +/- 15 yr [mean +/- standard deviation]) with mesial temporal sclerosis were treated with radiosurgical amygdalohippocampectomy (25 Gy to the 50% isodose region with a mean target volume of 6.2 +/- 0.7 cm). MRI and magnetic resonance spectroscopy were performed sequentially during a 24-month period after treatment.
Results: Patients were followed up clinically for 24 to 53 months. MRI scans revealed changes of marked temporal lobe swelling, with often markedly elevated apparent diffusion coefficients in keeping with vasogenic edema that became apparent 6 to 12 months after stereotactic radiosurgery. Spectroscopy of the target area revealed a progressive loss of N-acetylaspartate (the late evolution of lactate) and a peak in the choline-to-creatine ratio that seemed to coincide with the peak of the vasogenic edema in the temporal lobe surrounding the target area. Clinically, all patients showed some reduction in seizure frequency, although in two patients, this reduction was modest. The MRI changes in those patients were also modest, and three patients ultimately became free of seizures. However, there was a latency of 18 to 24 months before improvements in seizure control occurred, and during this period, seizures worsened or changed in four patients. Two patients also developed symptoms of increased intracranial pressure with mild dysphasia, which responded to administration of corticosteroid medication. However, no long-term clinical verbal memory decline was identified in any patient.
Conclusion: There are marked changes in MRI scans and magnetic resonance spectroscopic findings after patients undergo radiosurgery for temporal lobe epilepsy. Our initial findings suggest that some patients may have a period of distressing symptoms that accompany changes that are visualized on the MRI scans.