Voxel-based morphometric magnetic resonance imaging (MRI) postprocessing in MRI-negative epilepsies

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Objective:In the presurgical workup of magnetic resonance imaging (MRI)-negative (MRI or “nonlesional”) pharmacoresistant focal epilepsy (PFE) patients, discovering a previously undetected lesion can drastically change the evaluation and likely improve surgical outcome. Our study utilizes a voxel-based MRI postprocessing technique, implemented in a morphometric analysis program (MAP), to facilitate detection of subtle abnormalities in a consecutive cohort of MRI surgical candidates.Methods:Included in this retrospective study was a consecutive cohort of 150 MRI surgical patients. MAP was performed on T1-weighted MRI, with comparison to a scanner-specific normal database. Review and analysis of MAP were performed blinded to patients' clinical information. The pertinence of MAP+ areas was confirmed by surgical outcome and pathology.Results:MAP showed a 43% positive rate, sensitivity of 0.9, and specificity of 0.67. Overall, patients with the MAP+ region completely resected had the best seizure outcomes, followed by the MAP patients, and patients who had no/partial resection of the MAP+ region had the worst outcome (p < 0.001). Subgroup analysis revealed that visually identified subtle findings are more likely correct if also MAP+. False-positive rate in 52 normal controls was 2%. Surgical pathology of the resected MAP+ areas contained mainly non–balloon-cell focal cortical dysplasia (FCD). Multiple MAP+ regions were present in 7% of patients.Interpretation:MAP can be a practical and valuable tool to: (1) guide the search for subtle MRI abnormalities and (2) confirm visually identified questionable abnormalities in patients with PFE due to suspected FCD. A MAP+ region, when concordant with the patient's electroclinical presentation, should provide a legitimate target for surgical exploration. Ann Neurol 2015;77:1060–1075

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