Failed surgery for epilepsy - A study of persistence and recurrence of seizures following temporal resection

From a series of 282 consecutive temporal resections for medically intracta ble epilepsy associated with mesial temporal sclerosis (MTS), dysembryoplas tic neuroepithelial tumour (DNT) or non-specific pathology (NSP), 51 patien ts had persistent or recurrent seizures occurring at least monthly. Of thes e patients, 44 underwent detailed assessment of their postoperative seizure s, which included clinical evaluation, interictal and ictal EEG and high-re solution MRI, Of the 20 patients with MTS in the original pathology, 14 (70 %) had postoperative seizures arising In the hemisphere of the resection, t he majority (12 patients) in the temporal region. Although MRI demonstrated residual hippocampus in five of these 12 patients, only one patient was co nsidered to have seizures arising there, whilst the remainder had electrocl inical evidence of seizure onset in the neocortex. In contrast, five of the MTS relapses (25%) had seizure onset exclusively in the contralateral temp oral region. Among the 14 patients with non-specific pathology, relapse was also predominantly from the ipsilateral hemisphere (64%), but more relapse d from extratemporal sites compared with the MTS cases, including two with NSP who had occipital structural abnormalities. Although 70% of the 10 pati ents with DNT had postoperative partial seizures arising in the ipsilateral hemisphere, many (60%) had evidence of a more diffuse disorder with additi onal generalized seizures, cognitive and behavioural disturbance and multif ocal and generalized EEG abnormalities. Nine patients (20%) had immediate p ostoperative seizure-free periods of at least 1 year, and seven of these ha d MTS in the operative specimen. Of these seven patients, four had ipsilate ral temporal seizures and three had contralateral temporal seizures. Overal l, few missed lesions were discovered on postoperative MRI and reoperations were performed or considered possible in a minority of cases. Despite well -defined preoperative electroclinical syndromes of temporal lobe epilepsy, many patients relapsed unexpectedly, either immediately or remotely from th e time of surgery. Maturing epileptogenicity in a surgical scar was not, ho wever, considered to be a significant primary mechanism in patients who rel apsed after a seizure-free interval.