Role of ictal baseline shifts and ictal high-frequency oscillations in stereo-electroencephalography analysis of mesial temporal lobe seizures.
OBJECTIVE
To assess the role of ictal baseline shifts (IBS) and ictal high-frequency oscillations (iHFOs) in intracranial electroencephalography (EEG) presurgical evaluation by analysis of the spatial and temporal relationship of IBS, iHFOs with ictal conventional stereo-electroencephalography (icEEG) in mesial temporal lobe seizures (MTLS).


METHODS
We studied 15 adult patients with medically refractory MTLS who underwent monitoring with depth electrodes. Seventy-five ictal EEG recordings at 1,000 Hz sampling rate were studied. Visual comparison of icEEG, IBS, and iHFOs were performed using Nihon-Kohden Neurofax systems (acquisition range 0.016-300 Hz). Each recorded ictal EEG was analyzed with settings appropriate for displaying icEEG, IBS, and iHFOs.


RESULTS
IBS and iHFOs were observed in all patients and in 91% and 81% of intracranial seizures, respectively. IBS occurred before (22%), at (57%), or after (21%) icEEG onset. In contrast, iHFOs occurred at (30%) or after (70%) icEEG onset. The onset of iHFOs was 11.5 s later than IBS onset (p < 0.0001). All of the earliest onset of IBS and 70% of the onset of iHFOs overlapped with the ictal onset zone (IOZ). Compared with iHFOs, interictal HFOs (itHFOs) were less correlated with IOZ. In contrast to icEEG, IBS and iHFOs had smaller spatial distributions in 70% and 100% of the seizures, respectively. An IBS dipole was observed in 66% of the seizures. Eighty-seven percent of the dipoles had a negative pole at the anterior/medial part of amygdala/hippocampus complex (A-H complex) and a positive pole at the posterior/lateral part of the A-H complex.


CONCLUSIONS
The results suggest that evaluation of IBS and iHFOs, in addition to routine icEEG, helps in more accurately defining the IOZ. This study also shows that the onset and the spatial distribution of icEEG, IBS, and iHFOs do not overlap, suggesting that they reflect different cellular or network dynamics.
Department of Neurology, Adult Epilepsy Center, University of Chicago Medical Center, Chicago, Illinois, U.S.A.
Shasha
S
Wu
Department of Neurology, Metro Health Medical Center, Cleveland, Ohio, U.S.A.
Hari Prasad
HP
Kunhi Veedu
Department of Neurology, Epilepsy Center, University Hospitals, Case Medical Center, Cleveland, Ohio, U.S.A.
Samden D
SD
Lhatoo
Department of Neurology, Epilepsy Center, George Washington University, Washington, District of Columbia, U.S.A.
Mohamad Z
MZ
Koubeissi
Department of Neurosurgery, University Hospitals, Case Medical Center, Cleveland, Ohio, U.S.A.
Jonathan P
JP
Miller
Department of Neurology, Epilepsy Center, University Hospitals, Case Medical Center, Cleveland, Ohio, U.S.A.
Hans O
HO
Lüders
D000328:Adult; D000679:Amygdala / Q000503:physiopathology / Q000601:surgery; D038481:Anterior Temporal Lobectomy; D001931:Brain Mapping; D004292:Dominance, Cerebral / Q000502:physiology; D004567:Electrodes, Implanted; D004569:Electroencephalography / Q000379:methods*; D004833:Epilepsy, Temporal Lobe / Q000175:diagnosis* / Q000503:physiopathology* / Q000601:surgery; D005071:Evoked Potentials / Q000502:physiology*; D005260:Female; D019788:Fluorodeoxyglucose F18; D006624:Hippocampus / Q000473:pathology / Q000503:physiopathology / Q000601:surgery; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D009483:Neuropsychological Tests; D049268:Positron-Emission Tomography; D011183:Postoperative Complications / Q000175:diagnosis / Q000503:physiopathology; D012189:Retrospective Studies; D012598:Sclerosis; D012815:Signal Processing, Computer-Assisted; D013702:Temporal Lobe / Q000503:physiopathology / Q000601:surgery; D014057:Tomography, X-Ray Computed; D014741:Video Recording; D055815:Young Adult
D019788:Fluorodeoxyglucose F18
DC shifts; Depth intracranial monitoring; Fast ripples; Infraslow activity; Ripples