The Predictive Value of Interictal Scalp EEG Findings in Aiding the Detection of Malformations of Cortical Development in Temporal Lobe Epilepsy

Abstract

Abstract INTRODUCTION With the advent of minimally invasive surgical approaches for medically refractory epilepsy, we now have the ability to target specific epileptogenic foci with great precision. Previous studies have recognized the importance of complete resection of malformations of cortical development (MCD) in the success of epilepsy surgery. However, many of these lesions escape detection using standard epilepsy protocol MR imaging. This study seeks to evaluate the concurrence of radiographic and histopathologic findings of MCD in patients with refractory temporal lobe epilepsy (TLE) and describe the predictive value of interictal scalp EEG findings in the detection of MCD in an effort to inform surgical decision-making processes. METHODS We retrospectively identified 34 patients who underwent surgical resection for treatment of medically refractory TLE over a 10 yr period at Northwestern University. Preoperative MRI reports, VEEG reports, and postoperative surgical pathology reports were used to correlate radiographic findings of MCD with histopathologic findings of MCD and identify the predictive value of scalp video EEG (VEEG) abnormalities in the detection of MCD. RESULTS We found that 66.7% of focal cortical dysplasias (FCD) identified on pathology and all cases of histopathologically confirmed mild MCD were missed on preoperative MRI. The finding of a rhythmic or continuous interictal abnormality on preoperative VEEG corresponded to a sensitivity of 73.1% and a specificity of 62.5% in detecting either FCD or mild MCD. Of the patients who had a missed FCD on MRI, 80% had continuous or rhythmic interictal abnormalities on EEG. CONCLUSION MCDs are highly prevalent in medically refractory TLE and many of these MCDs are missed on preoperative MRI. The presence of a continuous and/or rhythmic interictal abnormality on scalp VEEG is suggestive of underlying MCD. The presence of one or both of these interictal findings may support the value of performing an intracranial EEG procedure prior to employing an ultraprecise minimally invasive surgical treatment option such as laser ablation.