Abstracts

Rationale: The orbitofrontal(OF) region is one of the least explored and least understood regions of the cerebral cortex. Epilepsy from the OF region is difficult to recognize and easy to misinterpret as either frontal lobe or temporal lobe epilepsy because semiology and clinical presentations are variable. In the setting of MRI negative epilepsy, surgical management of OF epilepsy is highly challenging. Here we aim to highlight the usefulness of voxel-based morphometric MRI post-processing in detecting subtle epileptogenic lesions in patients with OF epilepsy and no apparent lesions on the MRI Methods: Total of 9 OF epilepsy patients were included who met the following criteria: surgical resection of the OF lobe with/without adjacent cortex, Engel class 1 outcome for = 12 months following epilepsy surgery and pre-operative negative MRI. Patients were investigated in terms of their image post-processing and functional neuroimaging characteristics, electroclinical characteristics obtained from noninvasive and invasive evaluations, and pathological findings. MRI postprocessing was performed using a voxel-based morphometric analysis program (MAP) on preoperative T1-weighed Magnetization Prepared Rapid Acquisition with Gradient Echo (MPRAGE) images. A blinded reviewer used the z-score of 4 to identify highlighted areas on the junction file Results: The majority of patients (7 of 9) had MAP+ abnormality in the OF region. 6 patients had single-focus lesion, which was completely removed by resection. One patient had multiple (bilateral) lesions, with lesions on one side completely removed.  Although interictal and ictal scalp EEG correctly lateralized in the majority of patients, false localization to the temporal region occurred frequently. PET was obtained in all patients but of limited localization value. Ictal SPECT was successfully obtained in 7 of the 9 patients; in 4 patients, SISCOM showed hyperperfusion in the ipsilateral OF cortex in addition to several additional multilobar regions. MEG was recorded in 4 patients: 2 patients had lobar localization to the ipsilateral frontal lobe; one had a tight cluster in the ipsilateral postcentral gyrus; the other had a negative MEG. Intracranial EEG was performed in 8 patients which sufficiently covered the OF region, and exclusively pointed ictal onset to the OF region in all. The remaining one patient underwent resection guided by intraoperative ECoG which showed frequency discharges over right OF region. Six MAP+ patients had focal cortical dysplasia (FCD) pathology, including 1 type IIa and 5 type I. Conclusions: Our study highlights the heterogeneity of OF epilepsies in terms of neuroimaging and electrophysiological representation.Lesion or subtle changes in the OF cortex is difficult to identify visually due to the region’s complex gyral and sulcal convolutions. While careful interpretation of potential false positive results is needed, MRI post-processing techniques can be of crucial help in identifying subtle abnormalities associated with OF epilepsy. Funding: None