Intracranial EEG for seizure focus localization: evolving techniques, outcomes, complications, and utility of combining surface and depth electrodes

Abstract

<jats:sec><jats:title>OBJECTIVE</jats:title><jats:p>Intracranial electroencephalography (iEEG) provides valuable information that guides clinical decision-making in patients undergoing epilepsy surgery, but it carries technical challenges and risks. The technical approaches used and reported rates of complications vary across institutions and evolve over time with increasing experience. In this report, the authors describe the strategy at the University of Iowa using both surface and depth electrodes and analyze outcomes and complications.</jats:p></jats:sec><jats:sec><jats:title>METHODS</jats:title><jats:p>The authors performed a retrospective review and analysis of all patients who underwent craniotomy and electrode implantation from January 2006 through December 2015 at the University of Iowa Hospitals and Clinics. The basic demographic and clinical information was collected, including electrode coverage, monitoring results, outcomes, and complications. The correlations between clinically significant complications with various clinical variables were analyzed using multivariate analysis. The Fisher exact test was used to evaluate a change in the rate of complications over the study period.</jats:p></jats:sec><jats:sec><jats:title>RESULTS</jats:title><jats:p>Ninety-one patients (mean age 29 ± 14 years, range 3–62 years), including 22 pediatric patients, underwent iEEG. Subdural surface (grid and/or strip) electrodes were utilized in all patients, and depth electrodes were also placed in 89 (97.8%) patients. The total number of electrode contacts placed per patient averaged 151 ± 58. The duration of invasive monitoring averaged 12.0 ± 5.1 days. In 84 (92.3%) patients, a seizure focus was localized by ictal onset (82 cases) or inferred based on interictal discharges (2 patients). Localization was achieved based on data obtained from surface electrodes alone (29 patients), depth electrodes alone (13 patients), or a combination of both surface and depth electrodes (42 patients). Seventy-two (79.1%) patients ultimately underwent resective surgery. Forty-seven (65.3%) and 18 (25.0%) patients achieved modified Engel class I and II outcomes, respectively. The mean follow-up duration was 3.9 ± 2.9 (range 0.1–10.5) years. Clinically significant complications occurred in 8 patients, including hematoma in 3 (3.3%) patients, infection/osteomyelitis in 3 (3.3%) patients, and edema/compression in 2 (2.2%) patients. One patient developed a permanent neurological deficit (1.1%), and there were no deaths. The hemorrhagic and edema/compression complications correlated significantly with the total number of electrode contacts (p = 0.01), but not with age, a history of prior cranial surgery, laterality, monitoring duration, and the number of each electrode type. The small number of infectious complications precluded multivariate analysis. The number of complications decreased from 5 of 36 cases (13.9%) to 3 of 55 cases (5.5%) during the first and last 5 years, respectively, but this change was not statistically significant (p = 0.26).</jats:p></jats:sec><jats:sec><jats:title>CONCLUSIONS</jats:title><jats:p>An iEEG implantation strategy that makes use of both surface and depth electrodes is safe and effective at identifying seizure foci in patients with medically refractory epilepsy. With experience and iterative refinement of technical surgical details, the risk of complications has decreased over time.</jats:p></jats:sec>

The Potential for a Speech Brain–Computer Interface Using Chronic Electrocorticography

“…In their study, Hamer et al [106] noted that overall complication rate from 1980 to 1997 decreased from 26.3% over the past 23 years, including 1 mortality after grid implantation, to 19% over the past 5 years, including 2% permanent complications, and 13.5% over the past 3 years, with no mortalities or permanent complications. Similarly, Nagahama et al [110] noted that overall complication rates from 2006 to 2015 decreased from 13.9% over the first 5 years to 5.5% over the last 5 years, though this change was not statistically significant due to the low number of patients and relatively low complication rates over both periods. However, they assert nonetheless that improved surgical techniques have decreased complication rate [110].…”

“…Similarly, Nagahama et al [110] noted that overall complication rates from 2006 to 2015 decreased from 13.9% over the first 5 years to 5.5% over the last 5 years, though this change was not statistically significant due to the low number of patients and relatively low complication rates over both periods. However, they assert nonetheless that improved surgical techniques have decreased complication rate [110]. These include 1) elevated placement of the bone flap in combination with expansive duraplasty using a dural substitute, 2) meticuluous homeostasis of the dura following excision, and 3) suturing of the dural cuff to the craniotomy margin [110].…”

“…ECoG implantation for seizure monitoring prior to epilepsy surgery can serve as a useful reference point for the safety of implanting more electrodes than those of the RNS and NeuroVista systems mentioned, which typically implant no more than 8 to 12 electrodes. Multiple studies have assessed complication rate in hundreds of patients from acute intracranial monitoring, which typically employs 32 to 128 or more electrodes, and its change from past to present [105][106][107][108][109][110]. In their study, Hamer et al [106] noted that overall complication rate from 1980 to 1997 decreased from 26.3% over the past 23 years, including 1 mortality after grid implantation, to 19% over the past 5 years, including 2% permanent complications, and 13.5% over the past 3 years, with no mortalities or permanent complications.…”

Endovascular Neuromodulation: Safety Profile and Future Directions

“…Intracranial neuromodulation has numerous potential applications, including epilepsy monitoring (1,2), neurostimulation (3), thought to text and thought to speech paradigms (4)(5)(6), and control of robotic limbs and exoskeletons (7). A number of neural interfaces are in established clinical practice.…”

“…A number of neural interfaces are in established clinical practice. These include electrocorticography (ECoG) and intraparenchymal depth electrodes (1), which enable intracranial recording of neural signals, and deep brain stimulation (DBS) (3), which enables therapeutic stimulation of deep brain nuclei. Since their implantation requires craniotomy, these devices carry the risks of open brain surgery, such as hemorrhage, infection, postoperative pain, and prolonged recovery time (8)(9)(10)(11).…”