Original ArticleThe Brain is Not Flat: Conformal Electrode Arrays Diminish Complications of Subdural Electrode Implantation, A Series of 117 Cases
Introduction
Intracranial electrophysiology is integral to evaluating patients with epilepsy with poorly defined relationships between lesion and ictal onsets, or no obvious lesion,1, 2, 3, 4, 5 and localizes epileptogenic zone1,2,6,7 in 30%–50% of epilepsy surgery candidates.8,9 Over the last 5 years, there has been a shift from subdural electrodes (SDEs) to stereo-electroencephalography (SEEG) for intracranial evaluation of focal epilepsy. SEEG is safer, faster, and less painful and has better outcomes, particularly to evaluate nonlesional epilepsy.7,10, 11, 12, 13, 14, 15 When the putative focus of epilepsy is proximate to the language, motor, or visual cortex, SDEs may be necessary to ascertain the relative topography of seizure focus relative to the eloquent cortex.7,16, 17, 18, 19, 20, 21, 22, 23 In our practice SDEs are used to evaluate neocortical epilepsy around eloquent language cortex, and in young children, whose skull is too thin to hold anchor bolts for SEEG.
The prevalence of major complications in patients with SDE is difficult to estimate given variability across series and publication bias that results in underreporting adverse outcomes. Large systematic reviews and meta-analyses of adverse events related to SDE placement show a pooled prevalence of around 12%,7,8 with most common adverse events: intracranial hemorrhage (ICH), increased intracranial pressure (ICP), neurologic compromise, and superficial infections around 4.0%, 2.4%, 2.3% and 3.0%, respectively.7 The underlying reason for most of these complications is symptomatic extra-axial fluid/blood collections (sEFCs) causing mass effect, increased ICP, and neurologic compromise. Risk varies between 1% and 17% in large series.1, 2, 3, 4, 5,8,17,24, 25, 26 In such situations, electrodes are removed, extra-axial fluid collection (EFC) evacuated and intracranial electroencephalographic evaluation interrupted or terminated.
We identified imaging characteristics predicting complications in patients who require close observation and early intervention to minimize the impact of complications. We devised techniques to minimize risks by modifying the grid design, implantation technique, and patient management after implantation. We focus on adults who are at greater risk for these complications because they undergo monitoring longer than pediatric patients, because of lower seizure frequencies.
SDEs are platinum-iridium discs embedded within flat silastic sheets.27 They do not reliably conform to the convex surface of the cortex and may promote sEFC accumulation in the potential space between arrays and the concave inner surface of the dura and skull. After complications during the first 3 years, we made relaxing incisions to help them conform to the cortex, coupled with routine dural expansion using bovine xenograft after implantation and used a single exit site for all leads.
Section snippets
Methods
After approval by the local institutional committee for protection of human subjects and informed consent from patients (IRB number HSC-MS-06-0385), a prospective database of adults undergoing SDE implantation for medically refractory epilepsy was compiled. Data from patients undergoing SDE placement by the senior author from November 2004 to October 2017 were compiled, including demographics, number of electrodes, monitoring duration, length of implantation surgery, history of previous
Results
A total of 117 craniotomies were performed in 111 patients: 42 right-sided, 68 left-sided, and 7 bilateral. Six patients returned to the operating room for additional electrodes to be placed during the same hospital stay. The mean patient age was 33.7 years (range, 16–63 years), 59 patients (53%) were female, and there was a mean of 115 electrode contacts (standard deviation, 29.7; range, 60–254), and mean monitoring duration of 8.4 days (standard deviation, 3; range, 1–17). Postimplantation CT
Discussion
Intracranial recording is critical to evaluating patients with intractable epilepsy.1, 2, 3, 4 SDE implantation is simple in concept but fraught with myriad potential complications. We show that hemorrhagic neurologic complications can be anticipated by the degree of shift on postoperative MRI. After modifications in perioperative management, it is possible to minimize risks. Like in other centers, the number of electrodes implanted increases with experience and perhaps with complexity of cases.
Conclusions
The use of conformal subdural grids and routine dural augmentation may reduce complications of SDE implantation. Complications can be anticipated using routine MRI and measuring midline shift. Symptomatic subdural collections may be safely removed without terminating the intracranial evaluation, if appropriate steps are taken to enable this at implantation.
CRediT authorship contribution statement
Brian A. Tong: Formal analysis, Investigation, Software, Data curation, Writing - original draft, Writing - review & editing, Visualization. Yoshua Esquenazi: Investigation, Formal analysis, Data curation, Writing - original draft, Visualization. Jessica Johnson: Formal analysis, Data curation, Project administration. Ping Zhu: Formal analysis, Software, Resources, Validation. Nitin Tandon: Conceptualization, Formal analysis, Investigation, Supervision, Visualization, Validation, Methodology.
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Conflict of interest statement: The authors declare that the article content was composed in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.