Visual and Quantitative Ictal EEG Predictors of Outcome After Temporal Lobectomy

Authors

  • Bassam A. Assaf,

    Corresponding author
    1. Department of Neurology, Saint Louis University, St. Louis, Missouri
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  • John S. Ebersole

    1. Department of Neurology, Yale University School of Medicine, New Haven, and Neurology Service, Epilepsy Center, VA Connecticut Healthcare System, West Haven, Connecticut, U.S.A.
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Address correspondence and reprint requests to Dr. B. A. Assaf at Department of Neurology, Saint Louis University, 3635 Vista at Grand, St. Louis, MO 63110, U.S.A.

Abstract

Summary: Purpose: We investigated whether visual and quantitative ictal EEG analysis could predict surgical outcome after anteromesial temporal lobectomy (AMTL) in which mesial structures, basal, and temporal tip cortex were resected.

Methods: We retrospectively reviewed 282 presurgical scalp-recorded ictal EEGs (21- to 27-channel) from 75 patients who underwent AMTL. We examined the pattern of seizure onset (frequency, distribution, and evolution) and estimated the principal underlying cerebral generators by using a multiple fixed dipole model that decomposes temporal lobe activity into four sublobar sources (Focus 1.1). We correlated findings with a 2-year postoperative outcome.

Results: Sixteen patients had seizures with a well-lateralized, regular 5 to 9-Hz rhythm at onset, that most often had a temporal or subtemporal distribution. All patients became seizure free after surgery. In 51 patients, seizure onset was remarkable for lateralized slow rhythms (>5 Hz), which sometimes appeared as periodic discharges, were often irregular and stable only for short periods (>5 s), and had a widespread lateral temporal distribution. Among these a favorable surgical outcome was encountered in patients with seizures having prominent anterior-tip sources (16 of 17 seizure free), whereas those with dominant lateral or oblique sources had a less favorable outcome (three of 14 and 13 of 18, respectively). Irregular, nonlateralized slowing characterized seizure onsets in eight patients. Three patients became seizure free after surgery.

Conclusions: Both visual and quantitative sublobar source analysis of scalp ictal EEG can predict surgical outcome in most cases after AMTL and complement non-invasive presurgical evaluation.

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