Depth electroencephalography in selection of refractory epilepsy for surgery.

Depth electroencephalography (EEG) is sometimes used to evaluate medically refractory epileptic patients for surgical treatment. Surgical excision of well-defined epileptogenic foci has been shown repeatedly to cause a substantial reduction of seizure frequency in 60 to 80% of these patients; however, because surgical success is no better at centers that employ depth EEG in patient evaluation, the procedure remains controversial. Review of the available literature shows that depth EEG results reported to date, when compared to scalp EEG results in 178 patients, could have enabled selection of 36% more patients for surgery by defining otherwise unidentifiable single epileptogenic foci. Furthermore, depth EEG could have prevented surgery in another 18% by demonstrating different or additional epileptogenic foci in patients otherwise thought to have a single discharging focus amenable to resection. Thus depth EEG had the potential to alter the surgical decision in more than 50% of patients reported. Centers that employ depth EEG may evaluate a different population of patients, which could account for their lack of increased surgical success.