Intracranial monitoring using electroencephalography (IC-EEG) continues to play a critical role in the assessment of patients with medically intractable localization-related epilepsy. There has been minimal change in grid or electrode design in the last 15–20 years, and the surgical approaches for implantation are unchanged. Intracranial monitoring using EEG allows detailed definition of the region of ictal onset and defines the epileptogenic zone, particularly with regard to adjacent potentially eloquent tissue. Recent developments of IC-EEG include the coregistration of functional imaging data such as magnetoencephalography to the frameless navigation systems. Despite significant inherent limitations that are often overlooked, IC-EEG remains the gold standard for localization of the epileptogenic cortex. Intracranial electrodes take a variety of different forms and may be placed either in the subdural (subdural strips and grids, depth electrodes) or extradural spaces (sphenoidal, peg, and epidural electrodes). Each form has its own advantages and shortcomings but extensive subdural implantation of electrodes is most common and is most comprehensively discussed. The indications for intracranial electrodes are reviewed.
Advances in intracranial monitoring
Jeffrey P. Blount, Jason Cormier, Hyunmi Kim, Pongkiat Kankirawatana, Kristen O. Riley, and Robert C. Knowlton
Relative contribution of individual versus combined functional imaging studies in predicting seizure freedom in pediatric epilepsy surgery: an area under the curve analysis
Pongkiat Kankirawatana, Ismail S. Mohamed, Jason Lauer, Inmaculada Aban, Hyunmi Kim, Rong Li, Allan Harrison, AS, Monisha Goyal, Curtis J. Rozzelle, Robert Knowlton, and Jeffrey P. Blount
The goal of this study was to evaluate the predictive value and relative contribution of noninvasive presurgical functional imaging modalities based on the authors’ institutional experience in pursuing seizure-free surgical outcomes in children with medically refractory epilepsy.
This was a retrospective, single-institution, observational cohort study of pediatric patients who underwent evaluation and surgical treatment for medically refractory partial epilepsy between December 2003 and June 2016. During this interval, 108 children with medically refractory partial epilepsy underwent evaluation for localization and resective epilepsy surgery. Different noninvasive functional imaging modalities, including ictal SPECT, FDG-PET, and magnetoencephalography–magnetic source imaging, were utilized to augment a standardized paradigm (electroencephalography/semiology, MRI, and neuropsychology findings) for localization. Outcomes were evaluated at a minimum of 2 years (mean 7.5 years) utilizing area under the receiver operating characteristic curve analysis. Localizing modalities and other clinical covariates were examined in relation to long-term surgical outcomes.
There was variation in the contribution of each test, and no single presurgical workup modality could singularly and reliably predict a seizure-free outcome. However, concordance of presurgical modalities yielded a high predictive value. No difference in long-term outcomes between inconclusive (normal or diffusely abnormal) and abnormal focal MRI results were found. Long-term survival analyses revealed a statistically significant association between seizure freedom and patients with focal ictal EEG, early surgical intervention, and no history of generalized convulsions.
Comprehensive preoperative evaluation utilizing multiple noninvasive functional imaging modalities is not redundant and can improve pediatric epilepsy surgical outcomes.
Hemispherectomy Outcome Prediction Scale: a validity study
Andrew T. Hale, Dagoberto Estevez-Ordonez, Jana Badrani, Wen Sha, Anastasia Arynchyna-Smith, Monisha Goyal, Ismail Mohamed, Pongkiat Kankirawatana, Curtis J. Rozzelle, and Jeffrey P. Blount
Hemispherectomy is highly effective for patients with medically refractory epilepsy (MRE) arising from a single hemisphere. Recently, the Hemispherectomy Outcome Prediction Scale (HOPS) was developed as a prediction tool for seizure freedom after hemispherectomy. The authors’ goal was to perform a validation study to determine the generalizability of the HOPS score.
The authors present an observational, retrospective, 20-year, single-institution, two-surgeon experience using the lateral peri-insular hemispherectomy approach to validate the HOPS score. Variables used to derive the HOPS score included seizure onset age, semiology, PET hypometabolism, seizure substrate, and history of prior epilepsy resection. Multivariable logistic regression, multiple imputation, and Bayesian analyses were used to determine validity.
The authors’ cohort comprised 60 patients; 55% of patients were male and 78% were Caucasian. The median age at first hemispherectomy surgery was 72 months. At 1 year postoperatively, 80% of patients had Engel class I outcomes, analogous to most contemporary series. All patients who experienced seizure recurrence after hemispherectomy did so within the first 2 years postoperatively. Sixteen (27%) and 10 (17%) patients had contralateral MRI findings and hypometabolism on PET, respectively. Both a multivariable logistic regression model using HOPS score variables (model p = 0.2588) and a revised model that included contralateral MRI findings (model p = 0.4715) were not statistically significant in this cohort. Bayesian analysis also did not validate the HOPS score.
While seizure outcome prediction tools may be helpful for counseling patients about postoperative outcomes, rigorous validity and reliability testing are required. Prospective, standardized, and longitudinal evaluation of patients undergoing hemispherectomy are needed.
Surgical treatment of epilepsy in Vietnam: program development and international collaboration
Brandon G. Rocque, Matthew C. Davis, Samuel G. McClugage III, Dang Anh Tuan, Donald T. King III, Nguyen Thi Huong, Nguyen Thi Bich Van, Pongkiat Kankirawatana, Cao Vu Hung, Le Nam Thang, James M. Johnston, and Nguyen Duc Lien
The purpose of this report was to describe an international collaboration model to facilitate the surgical treatment of children with epilepsy in Vietnam.
This model uses three complementary methods to achieve a meaningful expansion in epilepsy surgery capacity: US-based providers visiting Hanoi, Vietnam; Vietnamese providers visiting the US; and ongoing telecollaboration, including case review and real-time mentorship using internet-based communication platforms.
Introductions took place during a US neurosurgeon’s visit to Vietnam in 2014. Given the Vietnamese surgeon’s expertise in intraventricular tumor surgery, the focus of the initial visit was corpus callosotomy. After two operations performed jointly, the Vietnamese surgeon went on to perform 10 more callosotomy procedures in the ensuing 6 months with excellent results. The collaborative work grew and matured in 2016–2017, with 40 pediatric epilepsy surgeries performed from 2015 through 2017. Because pediatric epilepsy care requires far more than neurosurgery, teams traveling to Vietnam included a pediatric neurologist and an electroencephalography (EEG) technologist. Also, in 2016–2017, a neurosurgeon, two neurologists, and an EEG nurse from Vietnam completed 2- to 3-month fellowships at Children’s of Alabama (COA) in the US. These experiences improved EEG capabilities and facilitated the development of intraoperative electrocorticography (ECoG), making nonlesional epilepsy treatment more feasible. The final component has been ongoing, i.e., regular communication. The Vietnamese team regularly sends case summaries for discussion to the COA epilepsy conference. Three patients in Vietnam have undergone resection guided by ECoG without the US team present, although there was communication via internet-based telecollaboration tools between Vietnamese and US EEG technologists. To date, two of these three patients remain seizure free. The Vietnamese team has presented the results of their epilepsy experience at two international functional and epilepsy surgery scientific meetings.
Ongoing international collaboration has improved the surgical care of epilepsy in Vietnam. Experience suggests that the combination of in-country and US-based training, augmented by long-distance telecollaboration, is an effective paradigm for increasing the capacity for highly subspecialized, multidisciplinary neurosurgical care.