Abstracts

Rationale: Temporal and orbitofrontal (OF) epilepsy can occur in combination or isolation, and can be difficult to differentiate by semiology and electroencephalogram (EEG) findings alone. In cases of suspected temporal or orbitofrontal epilepsy, sampling of both regions is routinely performed with subdural or intracerebral electrodes. By retrospective analysis of semiology, video-EEG (vEEG), imaging, and electrocorticography (ECoG), we sought to better characterize the relationship between these two epileptogenic areas. Methods: 20 consecutive patients were identified whose records indicated that temporal "plus" OF seizures were detected by intracranial recordings. All underwent invasive monitoring with grid and strip electrodes between 8/2006 and 12/2012 at an average of 17 years (range 5-49 years). Detailed review of clinical semiology, scalp EEG, MRI scans, and invasive monitoring was performed (Table 1). Chronic recordings were available for 19 of the 20 patients. MRI scans and scalp EEG's were available in all patients, but in 1 of the 20, no seizures were captured during the video EEG monitoring prior to surgery. Results: Scalp EEG/ semiology: 5 of the patients had focal temporal seizure onset with concordant semiology and no indication of frontal involvement, and 1 had temporal onset with fast spread to the ipsilateral more than the contralateral frontal polar region and temporal lobe semiology. 3 patients had temporal plus extra-temporal onsets (1 fronto-central with temporal semiology, 1 fronto-central with frontal semiology, and 1 posterior frontal-parietal onset with both temporal and frontal lobe semiology). 8 patients had uni-hemispheric non-localizing seizure onsets, in 1 case associated with pure temporal semiology, 5 cases of mixed temporal-frontal semiology, 1 fronto-central, and 1 case of pure frontal lobe semiology. 1 patient had non-lateralizing ictal findings with bilateral spikes and waves and clinical semiology suggesting one-sided seizure onsets. Radiology: MRI abnormalities were reported in 16 of the 20 patients. 6 patients had focal temporal lesions, including 4 cases of mesial temporal sclerosis (MTS, bilateral in 1 patient). The remaining 10 patients had more extensive MRI abnormalities that included temporal and extra-temporal regions in 4 patients, extra-temporal lesions only in 4 patients, and diffuse/ bilateral abnormalities in 2 patients. Intracranial recordings: 8 patients had simultaneous temporal and OF seizure onsets. In 4 patients, seizures originated in the temporal lobe and rapidly spread to the OF cortex. OF onset with rapid spread to the temporal lobe was seen in 3 patients. Independent OF and temporal onsets were seen in 3 patients. Conclusions: Our findings show that temporal "plus" epilepsy involving the OF cortex may be difficult to detect using non-invasive methods. Prior to invasive monitoring, the majority of patients had presumed temporal lobe epilepsy, and in all cases, the OF cortex involvement was definitively identified by subdural electrodes. Seizures may spread rapidly between the temporal and orbitofrontal structures, or arise concurrently/ independently in both areas, suggesting that the OF cortex may often be a potential source of surgical failure in temporal lobectomy cases. Funding: No external funding