Utility of invasive ictal EEG recordings in pre-surgical evaluation of patients with medically refractory temporal lobe epilepsy and normal MRI

PurposeSome previous studies have suggested that invasive ictal recording may be omitted in patients with medically refractory temporal lobe epilepsy (TLE) that have localizing scalp ictal recordings despite having normal magnetic resonance imaging (MRI). We investigated if and how often invasive ictal recording provided additional information to their pre-surgical evaluations.MethodsIn a retrospective review of 302 patients with intractable TLE who underwent pre-surgical evaluation between 1991 and 2006, we identified 45 patients who had normal MRI. Localization by scalp ictal recording, invasive ictal recording, and surgical procedures were obtained from medical records. Primary outcome was measured by comparing the concordance of localization by scalp and invasive ictal recordings and surgery to determine if invasive ictal recording provided additional information.ResultsTwenty-five patients were included in the analysis. Invasive ictal recordings were concordant in 72.0% (18/25) of the patients with unilateral temporal onset found on scalp ictal recording. 28.0% (7/25) of patients had their surgical plan altered by the results of invasive ictal recording. 61.1% (11/18) of patients who received anterior temporal lobectomies (ATL) remained seizure-free. Of the patients who received different surgeries based on invasive ictal recording, 80.0% (4/5) remained seizure-free.ConclusionsOur study showed that findings from invasive ictal recording changed the type of surgery in 28.0% of the patients. Invasive ictal recording may not be an absolute prerequisite for resective epilepsy surgery in some patients with intractable TLE with a supposedly normal MRI of the brain but may alter the surgical decision.