Abstracts

Rationale: MRI-negative ( nonlesional ) pharmacoresistant focal epilepsy (PFE) patients are a most challenging group for surgical management. In the presurgical workup of these patients, discovering a previously undetected lesion can drastically change the evaluation and treatment plan, and even the patient s surgical outcome. Our study utilizes a voxel-based MRI post-processing technique, implemented in a morphometric analysis program (MAP), to facilitate detection of subtle focal cortical dysplasia (FCD) in a consecutive cohort of MRI-negative surgical candidates.Methods: We retrospectively reviewed the consecutive surgical series of the Cleveland Clinic Epilepsy Center from 1999 to 2012. Patients were included if they: (1) had a preoperative 1.5T or 3T MRI; (2) were considered MRI negative prior to surgery; and (3) had > 12 months of postsurgical follow-up. MAP was performed on T1-weighed Magnetization Prepared Rapid Acquisition with Gradient Echo (MPRAGE) sequence in Matlab SPM5, consistent with methodology published by Huppertz et al. The gray-white junction z-score map was calculated by comparing the patient with a scanner-specific normal database. Regions with z-score > 4 were considered indicative of significant gray-white blurring. These areas were presented to a neuroradiologist (SEJ), who was the final judge of whether they present true lesions. The neuroradiologist was blinded to patients clinical information. The concordance among MAP focus and surgical resection was determined on a sublobar level. Surgical outcome at 12 months was dichotomized into two groups: seizure-free and not seizure-free. Statistical significance was assessed using Fisher s Exact test, with significance defined as p 0.05.Results: A total of 152 MRI-negative patients were identified (mean age = 28 years, 52% females, 43% seizure-free). MAP showed a 54% positive rate. Among MAP+ patients, 94% had a single-focus. In patients with a single MAP+ focus, the abnormality was completely resected in 61%. With complete resection of the MAP+ focus, 90% of patients were seizure-free, while only 15% of those with partial-resection/no-resection of the MAP focus were seizure-free. Representative patients are shown in the Figure. In the MAP negative group, 42% were seizure-free. Overall, once the MAP abnormality was completely resected, patients are more likely to become seizure-free, when compared with the partial-resection/no-resection group and the negative group (p<0.01). Surgical pathology of the resected MAP+ abnormalities contained mainly none-balloon-cell FCD. Multiple MAP+ abnormalities were present in 6% of patients; half of these patients were seizure-free with resection of one of the abnormalities concordant with the ictal onset on intracranial EEG.Conclusions: We present the largest-to-date cohort of MRI-negative epilepsy patients evaluated with MRI post-processing. MAP shows promise in identifying subtle FCD abnormalities that can be surgically targeted, and thus has the potential to improve surgical outcome of nonlesional epilepsies.