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  • Complication Rates of Subdural versus Depth Electrodes in 175 Patients Undergoing 210 Procedures for Invasive Monitoring in Epilepsy

    Final Number:

    Chengyuan Wu MD MSBmE; Kim A Williams MD; Mitchell Gil Maltenfort PhD; Justin Davanzo; James J. Evans MD; Ashwini Dayal Sharan MD

    Study Design:

    Subject Category:

    Meeting: Congress of Neurological Surgeons 2013 Annual Meeting

    Introduction: Intracranial monitoring has remained fundamental to epilepsy surgery. Associated complications include cerebral edema, subdural hematoma, epidural hematoma, infection, and cerebrospinal fluid (CSF) leak; which have a combined reported rate of 5-17%. Although several studies have highlighted risk factors such as number of implanted electrodes, number of trephinations, and occipital location,4 the risk associated with each electrode type has yet to be reported.

    Methods: We conducted a retrospective review of 175 consecutive patients with drug-resistant epilepsy who underwent 210 electrode implantation procedures between 2003 and 2011. A chart review was augmented by visual inspection of immediate postoperative images to verify documented findings. Incidental findings were noted but only symptomatic lesions were considered complications. When possible, findings were attributed to a particular electrode type.

    Results: This cohort included 95 men and 80 women ages 34±13 implanted with 1932 subdural electrodes (SDEs) and 451 depth electrodes (DEs) for 14.1±8.6 days. Logistic regression revealed significant predictors of postoperative radiographic findings to be prior craniotomy and number of implanted electrodes. The majority (74.5%) of radiographic findings were asymptomatic, particularly for extra-axial collections, contusions, and edema. Complications per SDE were 0.3% hemorrhage, 0.2% infarct, and 0.2% subdural collection; and per DE were 0.2% hemorrhage and 0% infarct. Although not related, both infection and CSF leak rates were 2.9%. One patient had status epilepticus and one died from cardiac arrest.

    Conclusions: In the largest cohort reported to date, the 9.0% cumulative complication rate is consistent with prior reports and upholds the safety of chronic invasive monitoring. Patients with prior craniotomies and greater number of implants appear to have higher complication rates. Further analysis has revealed complication rates of 1.0% per SDE and 0.2% per DE implanted. Possible explanations for this difference include increased micromotion, greater contact with pial vasculature, or increased mass effect of SDEs.

    Patient Care: Chronic invasive implants remain a critical element of the surgical evaluation of patients with drug-resistant epilepsy. This research continues to support their use as the overall complication rate remains low and in agreement with prior literature. Nevertheless, it is important to understand the complications involved and all variables associated with these complications. Not only does such knowledge allow us to better counsel patients, but it also serves as the first step towards minimizing complications. Specifically, our results should be factored into plans for the type and configuration of electrodes to be implanted.

    Learning Objectives: By the conclusion of this session, participants should be able to: 1) Understand that chronic intracranial monitoring for patients with drug-resistant epilepsy is generally safe. 2) Identify the major risk factors associated with chronic intracranial monitoring. 3) Discuss possible explanations for the increased complication rate of subdural electrodes found in our cohort.

    References: 1. Fountas KN. Implanted subdural electrodes: safety issues and complication avoidance. Neurosurgery clinics of North America. 2011;22(4):519–31, vii. Available at: Accessed April 3, 2013. 2. Burneo JG, Steven D a, McLachlan RS, Parrent AG. Morbidity associated with the use of intracranial electrodes for epilepsy surgery. The Canadian journal of neurological sciences. Le journal canadien des sciences neurologiques. 2006;33(2):223–7. Available at: 3. Van Gompel JJ, Worrell G a, Bell ML, et al. Intracranial electroencephalography with subdural grid electrodes: techniques, complications, and outcomes. Neurosurgery. 2008;63(3):498–505; discussion 505–6. doi:10.1227/01.NEU.0000324996.37228.F8. 4. Wellmer J, Von der Groeben F, Klarmann U, et al. Risks and benefits of invasive epilepsy surgery workup with implanted subdural and depth electrodes. Epilepsia. 2012;53(8):1322–32. doi:10.1111/j.1528-1167.2012.03545.x. 5. Morace R, Di Gennaro G, Picardi A, et al. Surgery after intracranial investigation with subdural electrodes in patients with drug-resistant focal epilepsy: outcome and complications. Neurosurgical review. 2012;35(4):519–26; discussion 526. Available at: Accessed April 5, 2013. 6. Neurology D, Population P. Complications of invasive subdural electrode monitoring at St. Louis Children’s Hospital, 1994–2005. 2006;105:343–347. 7. Wong CH, Birkett J, Byth K, et al. Risk factors for complications during intracranial electrode recording in presurgical evaluation of drug resistant partial epilepsy. Acta neurochirurgica. 2009;151(1):37–50. Available at: Accessed April 5, 2013. 8. Liu X, McCreery DB, Carter RR, Bullara L a, Yuen TG, Agnew WF. Stability of the interface between neural tissue and chronically implanted intracortical microelectrodes. IEEE transactions on rehabilitation engineering?: a publication of the IEEE Engineering in Medicine and Biology Society. 1999;7(3):315–26. Available at: 9. Biran R, Martin DC, Tresco PA. The brain tissue response to implanted silicon microelectrode arrays is increased when the device is tethered to the skull. 2007. doi:10.1002/jbm.a. 10. Thelin J, Jörntell H, Psouni E, et al. Implant size and fixation mode strongly influence tissue reactions in the CNS. PloS one. 2011;6(1):e16267. doi:10.1371/journal.pone.0016267.

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