Neuroimaging characteristics of MRI-negative orbitofrontal epilepsy with focus on voxel-based morphometric MRI postprocessing.
PURPOSE
The orbitofrontal (OF) region is one of the least explored regions of the cerebral cortex. There are few studies on patients with electrophysiologically and surgically confirmed OF epilepsy and a negative magnetic resonance imaging (MRI) study. We aimed to examine the neuroimaging characteristics of MRI-negative OF epilepsy with the focus on a voxel-based morphometric MRI postprocessing technique.


METHODS
We included six patients with OF epilepsy, who met the following criteria: surgical resection of the OF lobe with/without adjacent cortex, seizure-free for ≥12 months, invasive video-electroencephalography (EEG) monitoring showing ictal onset from the OF area, and preoperative MRI regarded as negative. Patients were investigated in terms of their image postprocessing and functional neuroimaging characteristics, electroclinical characteristics obtained from noninvasive and invasive evaluations, and surgical pathology. MRI postprocessing on T1 -weighted high-resolution scans was implemented with a morphometric analysis program (MAP) in MATLAB.


KEY FINDINGS
Single MAP+ abnormalities were found in four patients; three were in the OF region and one in the ipsilateral mesial frontal area. These abnormalities were included in the resection. One patient had bilateral MAP+ abnormalities in the OF region, with the ipsilateral one completely removed. The MAP+ foci were concordant with invasive electrophysiologic data in the majority of MAP+ patients (four of five). The localization value of 18F-fluorodeoxyglucose-positron emission tomography (FDG-PET) and ictal single-photon emission computed tomography (SPECT) is low in this cohort. Surgical pathology included focal cortical dysplasia, remote infarct, Rosenthal fiber formation and gliosis.


SIGNIFICANCE
Our study highlights the importance of MRI postprocessing in the process of presurgical evaluation of patients with suspected orbitofrontal epilepsy and "normal" MRI. Using MAP, we were able to positively identify subtle focal abnormalities in the majority of the patients. MAP results need to be interpreted in the context of their electroclinical findings and can provide valuable targets in the process of planning invasive evaluation.
['Wang|Z Irene|ZI|', 'Ristic|Aleksandar J|AJ|', 'Wong|Chong H|CH|', 'Jones|Stephen E|SE|', 'Najm|Imad M|IM|', 'Schneider|Felix|F|', 'Wang|Shuang|S|', 'Gonzalez-Martinez|Jorge A|JA|', 'Bingaman|W|W|', 'Alexopoulos|Andreas V|AV|']
D000293:Adolescent D000328:Adult D001426:Bacterial Proteins D001921:Brain D002648:Child D004569:Electroencephalography D017034:Epilepsy, Frontal Lobe D005098:Exotoxins D005260:Female D059907:Functional Neuroimaging D006801:Humans D007091:Image Processing, Computer-Assisted D008279:Magnetic Resonance Imaging D008297:Male D008875:Middle Aged D059906:Neuroimaging D049268:Positron-Emission Tomography D055815:Young Adult
Orbitofrontal epilepsy Epilepsy MRI MRI postprocessing Focal cortical dysplasia Presurgical evaluation MRI-negative epilepsy Voxel-based morphometry