title: Ictal depth EEG and MRI structural evidence for two different epileptogenic networks in mesial temporal lobe epilepsy.
abstract: Hypersynchronous (HYP) and low voltage fast (LVF) activity are two separate ictal depth EEG onsets patterns often recorded in presurgical patients with MTLE. Evidence suggests the mechanisms generating HYP and LVF onset seizures are distinct, including differential involvement of hippocampal and extra-hippocampal sites. Yet the extent of extra-hippocampal structural alterations, which could support these two common seizures, is not known. In the current study, preoperative MRI from 24 patients with HYP or LVF onset seizures were analyzed to determine changes in cortical thickness and relate structural changes to spatiotemporal properties of the ictal EEG. Overall, onset and initial ipsilateral spread of HYP onset seizures involved mesial temporal structures, whereas LVF onset seizures involved mesial and lateral temporal as well as orbitofrontal cortex. MRI analysis found reduced cortical thickness correlated with longer duration of epilepsy. However, in patients with HYP onsets, the most affected areas were on the medial surface of each hemisphere, including parahippocampal regions and cingulate gyrus, whereas in patients with LVF onsets, the lateral surface of the anterior temporal lobe and orbitofrontal cortex showed the greatest effect. Most patients with HYP onset seizures were seizure-free after resective surgery, while a higher proportion of patients with LVF onset seizures had only worthwhile improvement. Our findings confirm the view that recurrent seizures cause progressive changes in cortical thickness, and provide information concerning the structural basis of two different epileptogenic networks responsible for MTLE. One, identified by HYP ictal onsets, chiefly involves hippocampus and is associated with excellent outcome after standardized anteromedial temporal resection, while the other also involves lateral temporal and orbitofrontal cortex and a seizure-free surgical outcome occurs less after this procedure. These results suggest that a more extensive tailored resection may be required for patients with the second type of MTLE.
authors: Department of Neurology, David Geffen School of Medicine at UCLA, Los Angeles, CA, United States of America.
authors: Negar
authors: N
authors: Memarian
authors: Department of Neurology, Imaging Genetics Center, Institute for Neuroimaging and Informatics, Keck School of Medicine, University of Southern California, Los Angeles, CA, United States of America.
authors: Sarah K
authors: SK
authors: Madsen
authors: UCLA School of Nursing, University of California Los Angeles, Los Angeles, CA, United States of America.
authors: Paul M
authors: PM
authors: Macey
authors: Department of Neurosurgery, David Geffen School of Medicine at UCLA, Los Angeles, CA, United States of America.
authors: Itzhak
authors: I
authors: Fried
authors: Department of Neurology, David Geffen School of Medicine at UCLA, Los Angeles, CA, United States of America; Department of Neurobiology, David Geffen School of Medicine at UCLA, Los Angeles, CA, United States of America; Department of Psychiatry & Biobehavioral Sciences, David Geffen School of Medicine at UCLA, Los Angeles, CA, United States of America.
authors: Jerome
authors: J
authors: Engel
authors: Department of Neurology, Imaging Genetics Center, Institute for Neuroimaging and Informatics, Keck School of Medicine, University of Southern California, Los Angeles, CA, United States of America.
authors: Paul M
authors: PM
authors: Thompson
authors: Department of Neurology, David Geffen School of Medicine at UCLA, Los Angeles, CA, United States of America.
authors: Richard J
authors: RJ
authors: Staba
mesh_terms: D000328:Adult; D001931:Brain Mapping / Q000379:methods*; D004569:Electroencephalography / Q000379:methods*; D004833:Epilepsy, Temporal Lobe / Q000145:classification* / Q000503:physiopathology*; D005260:Female; D007839:Functional Laterality; D006624:Hippocampus / Q000473:pathology*; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D012189:Retrospective Studies