The predictive value of interictal scalp EEG findings in aiding the detection of malformations of cortical development in temporal lobe epilepsy and impact on surgical planning

BackgroundComplete resection of focal malformations of cortical development (MCD) has been recognized as crucial for the success of epilepsy surgery. However, many of these lesions escape detection using even state-of-the-art epilepsy protocol MRI imaging. This study evaluates the concurrence of radiographic and histopathologic findings of MCD in patients with refractory temporal lobe epilepsy (TLE) and defines the predictive value of EEG findings in the detection of MCD. Materials and MethodsPre-operative MRI, scalp VEEG, and post-operative surgical pathology reports from 34 consecutive patients treated for refractory TLE by surgical resection over a ten year period were included in analysis. Radiographic findings of MCD were correlated with histopathologic findings of MCD and compared against pre-operative interictal scalp EEG findings. Results66.7% of focal cortical dysplasias (FCD) identified on pathology and all cases of mild MCD (mMCD) were missed on pre-operative MRI. The description of a rhythmic or continuous interictal abnormality on pre-operative VEEG corresponds to a sensitivity of 73.1% and a specificity of 62.5% in detecting either FCD or mMCD. Of the patients who had a radiographically occult FCD, 80% had either a continuous or rhythmic interictal abnormality described in the interpretation of their pre-operative VEEG. ConclusionThis study highlights the high prevalence of MCDs in refractory TLE and the high rate of missed MCDs on pre-operative MRI. Findings here suggest that pre-operative scalp EEG may be able to provide additional information in the pre-operative detection of MCDs and therefore inform surgical decision making.