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  • Interhemispheric Subdural Electrodes (IHSE): Utility, Technique and Safety

    Final Number:

    Tarek Abuelem MD; David Elliot Friedman; Satish Agadi; Angus A. Wilfong MD; Daniel Yoshor MD

    Study Design:
    Clinical Trial

    Subject Category:

    Meeting: Congress of Neurological Surgeons 2011 Annual Meeting

    Introduction: Invasive monitoring using subdural electrodes is valuable for characterizing the epileptic zone in patients with intractable localization-related epilepsy. It is particularly critical for cases when scalp EEG is non-localizing, as is common with seizures originating in the interhemispheric region. For this reason, interhemispheric grid coverage can be especially valuable, but placement of an adequate array of IHSE presents a unique technical challenge, primarily due to the presence of bridging veins. We describe our operative technique for implantation of IHSE, and analyze our experience to better understand the utility, technical challenges, and safety of invasive monitoring in the interhemispheric region

    Methods: We identified 24 patients with IHSE placed by a single neurosurgeon since 2003. Generous midline exposure, meticulous preservation of veins, and sharp micro-dissection of the interhemispheric corridor were employed to facilitate grid placement under direct visualization. Records and images were reviewed to define the indications for interhemispheric coverage, number of grids and electrode contacts placed, duration and results of monitoring and mapping, type of resection, and complications

    Results: The number of implanted IHSE contacts (1cm inter-electrode distance) ranged from 10-106 (mean=39.8) per patient, including double-sided contacts. Monitoring lasted for 5.5 days on average (range 2-24days), with an adequate sample of seizures captured in all patients prior to explantation. Among patients implanted with IHSE, monitoring led to a paramedian cortical resection in 67%. One patient had grid-related mass effect, but was nonetheless able to complete monitoring. No other patient experienced any complications related to grid implantation and monitoring, although post-resection SMA syndromes were common and expected

    Conclusions: IHSE placement under direct visualization allows for extensive coverage of paramedian cortex with a low incidence of complications. When clinical factors suggest an epileptic focus near the midline, IHSE are useful in defining the epileptic zone, mapping cortical function and tailoring the eventual surgical resection

    Patient Care: Improve epilepsy localization and surgical treatment

    Learning Objectives: 1- IHSE placement is very useful in detecting seizures arizing from the paramedian cortical areas 2- IHSE placement is safe, with a complication rate no higher than convexity subdural electrodes 3- When clinically indicated, IHSE placement with adequate coverage should be encouraged


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