Persistent or recurrent seizures occurring at least monthly are reported in 51 (18%) of a series of 282 consecutive temporal resections for medically intractable epilepsy performed at Kings College Hospital, London, UK. Mean age at original surgery was 26 years (range 4 to 59 years), and the mean follow-up interval to reassessment was 6 years (range 3-17 yrs). Detailed assessment of postoperative seizures showed that of 20 with mesial temporal sclerosis (MTS), 14 (70%) had seizures arising in the hemisphere of the resection, and 35% from the contralateral hemisphere. Of 10 patients with dysembryoplastic neuroepithelial tumor (DNT), 70% had postoperative partial seizures arising in the ipsilateral hemisphere, but 60% had additional generalized seizures, cognitive, and behavioral disturbance, with multifocal and generalized EEG abnormalities. Nine (20%) patients had immediate seizure-free periods of at least 1 year, and 7 of these had MTS. On relapse of the 7, 4 had ipsilateral and 3 had contralateral temporal seizures. After postoperative MRI, only one missed structural lesion was uncovered, and reoperations were possible in a minority of cases. The majority of seizures with MTS were extrahippocampal. In the majority of surgical failures, the epileptogenic lesion was either extrahippocampal or extratemporal. Acoustic auras and EEG evidence of neocortical seizure origin in some might have indicated a preoperative poor outcome. Emerging improved MRI may demonstrate subtle cortical abnormalities responsible for operative failures. Patients should be counselled concerning the unpredictable nature of postoperative relapse. 
COMMENT. Despite extensive electroclinical and neuroimaging evaluation of temporal lobe epilepsy, approximately 20% relapse with persistent and recurrent seizures postoperatively, either immediately or after a 12 month seizure-free interval. Until more sophisticated MRI techniques are developed, patients should be aware of the unpredictable outcome.