Temporal lobe epilepsy: When are invasive recordings needed?

Temporal lobe epilepsy (TLE) is the most common type of medically intractab le partial epilepsy amenable to surgery. In the majority of cases, the unde rlying pathology in temporal lobe epilepsy is mesial temporal sclerosis (MT S). Whereas historically invasive recordings were required for most epileps y surgeries, indications have dramatically changed since the introduction o f high-resolution MRI, which uncovers structural lesions in a high percenta ge of cases. No invasive recordings are required to perform a temporal lobe ctomy in patients with intractable epilepsy who have structural imaging sug gesting unilateral MTS and concordant interictal and ictal surface EEG reco rdings, functional imaging, and clinical Findings. Invasive testing is need ed if there is evidence of bitemporal MTS on structural imaging and/or elec trophysiologically, and additional information from functional imaging, neu ropsychology, and the intracarotid amobarbital (Wada) test also does not he lp to lateralize the epileptogenic zone. Depth electrodes can be particular ly helpful in this setting. However, no surgery is indicated, even without invasive recordings, if bitemporal-independent seizures are recorded by sur face EEG and all additional testing is inconclusive. Other etiologies of TL E such as a tumor, vascular malformation, encephalomalacia, or congenital d evelopmental abnormality account for about 30% of all patients who undergo epilepsy surgery. Epilepsy surgery is indicated after limited electrophysio logic investigations if neuroimaging and electrophysiology converge. Howeve r, approaches for resection in lesional temporal lobe epilepsy vary among c enters. Completeness of resection is crucial and invasive recordings may be needed to guide the resection by mapping eloquent cortex and/or to determi ne the extent of the non-MRI-visible epileptogenic area. Specific approache s for the different pathologies are discussed because there is evidence tha t the relationship between the lesions visible on MRI and the epileptogenic zone varies among lesions of different pathologies, and therefore variable surgical strategies must be applied.