Abstracts

Rationale: One of the main challenges in epilepsy surgery is to remove sufficient epileptogenic tissue without compromising function. The most precise technique used to identify motor, sensory and language cortex is electrical stimulation mapping. Although stimulation mapping has been a standard clinical procedure since the 1950s, its lack of standardization risks variability in its sensitivity and specificity for identifying eloquent cortex. We developed and distributed an extra-operative neurostimulation mapping survey to gather information regarding current practices, and to begin to identify areas that could benefit from empirically determined guidelines.Methods: The survey consisted of 31 multiple choice or fill-in questions addressing topics such as selection of language tasks, criteria for identification of positive and negative functional sites, technical stimulation parameters, and management of mapping complications such as afterdischarges. Importantly, questions regarding adverse events were included. Epilepsy surgery programs were identified via the NAEC (National Association of Epilepsy Centers) website: http://www.naec-epilepsy.org/find.html, the ILAE website: http://www.ilae-epilepsy.org, and additional internet searching. A questionnaire and cover letter were mailed to each program with instructions that the questionnaire be completed by the individual(s) who routinely conduct stimulation mapping. Two hundred twenty questionnaires were mailed or emailed, 137 to North American sites and 83 to sites abroad. Preliminary descriptive statistics were calculated from the responses obtained to date.Results: Fifty-four surgery programs returned completed questionnaires. Sixty-nine percent of respondents were from North America, 16% were from Europe, and the remainder were from surgery centers abroad. Overall, responses revealed marked variability in virtually all aspects of current practice. A striking level of variability, i.e., < 60% agreement, was observed for the following: Percent error criteria for determining whether a site is positive, distance from positive sites to resection margin, duration of stimulation, maximum and minimum current settings, electrode pairing technique (e.g., remote, adjacent), definition of afterdischarge, and medication management with regard to stimulation mapping. Forty percent of respondents reported a persistent postoperative language deficit despite preservation of stimulation-identified language sites.Conclusions: There is marked variability in clinical practice of all aspects of stimulation mapping. Key areas that may merit further investigation include maximum stimulator settings, electrode pairing technique, identification and management of afterdischarges, criteria for positive site identification, and distance from resection margin. The high rate of persistent postoperative language deficits despite preservation of stimulation-identified positive sites likely reflects the use of ineffective techniques for a potentially highly sensitive procedure. Establishing empirically based guidelines to maximize functional outcome is warranted.