Authors :
Presenting Author: Noam Bosak, MD, PhD – Monash University
Terrence J. O'Brien, MB, BS, MD, FRACP, FRCPE, FAHMS, FAES – Monash University, Melbourne, VIC, Australia
Martin Hunn, MBChB, PhD, FRACS – Monash University
Matthew Gutman, MBBS, DipYW, FRACS – Monash University
Thanomporn Wittayacharoenpong, B.Eng, M.Eng – Monash University
Jacob Bunyamin, MD, MSC – Monash University
Parveen Sagar, MBBS, FRACP – Monash University
Haris Hakeem, MBBS, FCPS, FRACP – Monash University
Joshua Laing, BBiomedSci, MBBS, FRACP, PhD – Monash University
Patrick Kwan, BMedSci, BM, BChir, FRACP, PhD, FAHMS – Monash Institute of Medical Engineering, Monash Univeristy
Andrew Neal, MBBS, BMedSci, FRACP, PhD – Monash University
Rationale:
Understanding hippocampal (HC) epileptogenicity is crucially important for surgical decision-making, even amongst patients with presumed extra-HC epileptogenic zone (EZ). We utilised SEEG to characterise hippocampal epileptogenicity spectrum in temporal and extra-temporal drug-resistant epilepsy.Methods:
Consecutive SEEG patients with any implanted HC electrode were reviewed, and their HC categorized as: i) Primarily Epileptogenic Hippocampus (PEH) if included in the EZ based on multi-disciplinary team consensus, ii) Secondarily Epileptogenic Hippocampus (SEH) if not part of EZ but could generate spontaneous sub/clinical seizures and/or a clinical seizure following 1Hz stimulation and iii) Non-Epileptogenic Hippocampus for all other (NIH).
The maximal interictal spike and high frequency oscillation rates, and their geometric mean were computed per HC. Each habitual seizure was analysed with regards to HC onset or propagation for: the initial electrographic pattern within the HC categorized to high/low association with seizure freedom (SF) probability, the time from onset to hippocampal involvement (TTH) and the proportion of propagated seizures with fast activity ( >14Hz; FA) at any point. The proportion of extra-HC-onset seizures that propagated to a certain HC was defined as its propagation proportion (PP).
Finally, we compared patients with uni/bi-lateral SEH (SEHP) to the rest (non-SEHP) clinically and demographically. Given common bilateral epileptogenicity in mesial temporal lobe (mTLE), unilaterally sampled cases with this diagnosis were excluded.
Results:
We reviewed 287 seizures from 88 HC of 54 patients, 29 categorised as PEH, 28 as SEH (15 based only on stimulated seizures) and 31 as NIH. SEH were ipsilateral to the EZ in 29 bilaterally sampled cases, and contralateral only in 4, all mTLE.
Interictal epileptogenicity biomarkers did not differ between PEH and SEH, but were higher for both relative to NIH (P< 0.001). SEH showed higher PP than NIH (P=0.002), and the propagated activity was more likely to include FA (P=0.002), but their TTH was similar. The initial electrographic pattern was more commonly of the high SF probability category in HC-onset seizures relative to propagated seizures (65% vs 10%, P< 0.001), regardless of HC category. See Table 1.