Abstracts

Rationale: Focal resective surgery is the most effective treatment for medically intractable partial epilepsy, especially in patients with an identifiable focal lesion on magnetic resonance imaging (MRI). The lack of an identifiable focal lesion on MRI has been shown as a predictor for poor surgical outcome. Focal cortical dysplasia (FCD) is the most common underlying pathology in epilepsies with apparently normal MRI. The MRI features of FCD include abnormal cortical thickness, abnormal sulcal pattern, blurring of the gray-white matter junction, and abnormal signal in the white and/or gray matter. MRI post-processing has been demonstrated to be effective in identifying subtle focal cortical dysplasia in patients whose MRI scans were interpreted as normal by visual analysis. In studies conducted with adult cohorts, FCD detection was improved with computational techniques, but the validity of these techniques has not been established in the pediatric population. The purpose of this research is to assess the utility of a morphometric analysis program (MAP) in the detection of subtle cortical dysplasia in pediatric patients with refractory focal epilepsy. Methods: This is a retrospective non-interventional study performed at a level 4 epilepsy center. We included 34 consecutive MRI-negative pediatric patients (age 2-18 years) who underwent resective epilepsy surgery or intracranial electrode implantation. Automated Morphometric Analysis Program (MAP) analysis was performed against a control group of 40 pediatric patients with normal MRI obtained for reasons other than seizures (vomiting, double vision or dizziness). The control group included 20 MRI scans in the age group 2-6 years and 20 scans in the age group 6-14 years. Patients above 14 years of age were referenced to a normative adult database. Two MAP features were assessed; abnormal extension of gray matter into white matter and blurring of the gray-white matter junction. Generated z-score maps derived from T1 images, referenced to healthy pediatric controls for each of 34 cases were compared to the results of intracranial EEG, surgical resection and resection pathology results if available. Both absence of focal MAP positive areas or presence of symmetric MAP changes on both hemispheres were classified as MAP negative (MAP-ve). Results: 12 cases were classified as MAP-ve (35%). MAP identified focal lesions that were concordant with the surgical resection region or intracranial EEG findings in 12 patients (35%). The remaining nine patients showed either multifocal MAP lesions or MAP lesions discordant with surgical resection. Surgical pathology was available in 25/34 patients. The remaining nine patients underwent laser ablation (n=3) or no resection (n=6). Among the 25 patients who underwent resection, pathological examination in 10 patients revealed FCD IIA (four MAP +ve), two patients as FCD IIA/IC (both MAP +ve), seven patients FCD 1C (two MAP +ve), three patients as FCD IIB (two MAP +ve), two patients 1A (one MAP +ve) and one patient with gliosis (MAP -ve). Conclusions: Automatic morphometric analysis complements presurgical evaluation in pediatric patients with MRI negative refractory focal epilepsy and can detect subtle FCD in one third of patients. False positive results are more common than in adults, probably reflective of maturational changes in the pediatric age group. Funding: Kaul Pediatric Research InstituteNSF-EPSCoR