Synchronous recording of intracranial and extracranial EEG in temporal lobe epilepsy

SummaryPurposeTo explore the diagnostic value of intracranial electrodes in highly suspected temporal lobe epilepsy (TLE) and the value of sphenoid electrodes (PG) and the propagation patterns of ictal discharges in focus lateralization.MethodsIntracranial electrodes were implanted in 22 probable TLE patients through bilateral temporal burr holes. Extracranial electrodes included the 10-20 international EEG system and bilateral PGs. Intracranial and extracranial EEGs (IEEG, EEEG) were synchronously recorded. The interictal epileptic discharges (IEDs) were counted for 3 h of interictal preoperative long-playing video EEG. Time intervals between electrodes recording the ictus and ictus occurring were measured and the propagation patterns were deduced.ResultsBy IEEG, 18 patients with confirmed TLE had surgery; 14 were seizure-free. 3 had FLE, and 1, uncertain localization. Of the 14 TLE and postoperative seizure-free patients, the ratio (left:right) of IEDs in the 3 h interictal EEG was 483:211 in the 6 left TLE and 263:654 in the 8 right TLE. In 12 of the 14 cases, the side with more IEDs at PG was the epileptic focus side. In 11 of the 14 cases the earlier PG recording side was focus side. We found that the propagation sequence of ictus followed certain rules in most attacks.ConclusionsThe results indicated that IEEG was useful for final diagnosis of highly suspected TLE and that PG was helpful in focus lateralization. The propagation patterns of ictus might provide a new tool in focus lateralization and localization.