Abstracts

Rationale: Mesial temporal lobe epilepsy (MTLE) can be medically refractory yet surgically amenable. Pre-surgical evaluation with scalp recordings is not always sufficient to localize ictal onsets. Intracranial evaluation is challenging in patients with normal MRI. Multi-contact FOEs placed under fluoroscopic guidance sample the mesial temporal region and complement scalp electrodes in identifying MTLE seizure foci. We compared the utility of FOE recordings in the pre-surgical evaluation of lesional and non-lesional patients suspected to have MTLE in whom scalp recordings did not provide adequate localization for a surgical decision.Methods: We retrospectively reviewed 53 suspected MTLE patients who underwent both Phase-I scalp and Phase-II scalp-and-FOE recordings at UCSD. We studied two groups: Lesional cases (N=41) had identifiable MRI abnormalities (66% mesial temporal sclerosis), and Non-Lesional cases (N=12) had normal MRI. In each group, we quantified the impact of scalp and FOE recordings in the decision to proceed to surgery, exclude from surgery, or recommend additional evaluation.Results: 1) Lesional cases: - Phase-I identified 4 (9.8%) as possible good surgical candidates, excluded zero, and was indeterminate in 37 (90.2%). - FOE identified 31 (75.6%) as good surgical candidates who were referred for surgery without additional monitoring. 4 (9.8%) were excluded from surgery based on bilateral independent mesial temporal onsets. 6 (14.6%) had seizure onset outside the MTL, requiring further study. - Outcomes: 24 had surgery based on FOE results. The average frequency of seizures decreased from 9.9±13.2 per month pre-surgery to 0.02±0.07 per month post-surgery. 2) Non-lesional cases: - Phase-I identified 2 (16.7%) as possible good surgical candidates, excluded zero, and was indeterminate in 10 (83.3%) - FOE identified 5 (41.7%) as good surgical candidates who were referred for surgery without additional monitoring. 2 (16.7%) were excluded from surgery. 5 (41.7%) had seizure onset outside the MTL; of these, 1 had subdural grid simultaneously with FOEs, and had successful surgery based on the results of the grid. - Outcomes: 4 had surgery based on FOE results. The average frequency of seizures decreased from 11.5±2.95 per month before surgery to zero per month after surgery. 1 had surgery based on grid results, and seizures decreased from 4 per month pre-surgery to zero per month post-surgery.Conclusions: FOE monitoring was useful in the pre-surgical evaluation of suspected MTLE (for lesional and non-lesional cases) both in identifying surgical candidates and in excluding patients from surgery, while avoiding invasive intracranial monitoring in a large proportion of cases. Of note, bilateral independent MTLE seizure onsets were seen in the lesional group in nearly 10% of cases and in the non-lesional group in nearly 17% of cases. The good surgical outcomes (follow up 6 months to 5 years) demonstrate that evaluation with FOEs is a viable alternative to conventional invasive recordings for accurate localization of MTLE foci.