Abstracts

Rationale: Electrocorticography (ECoG) and electrical cortical stimulation (ECS) are often used in tandem to map eloquent cortex during neurosurgical procedures involving brain.  Eloquent cortex is important to identify for surgical planning and prediction of postoperative neurological function. Intraoperative seizures are a concern during awake craniotomy by limiting further behavioral testing, extending surgical exposure, and increasing morbidity.  Because a significant majority of patients with brain lesions manifest seizures, epileptiform discharges are also of interest.  To investigate the frequency of epileptiform discharges we evaluated high-density ECoG (HD-ECoG) during ECS to evaluate epileptiform abnormalities and post-surgical complications.  Methods: Intraoperative lesionectomy in/near eloquent cortex was performed using high-density ECoG (HD-ECoG) in combination with ECS between November 2016 and June 2017. HD-ECoG was performed with an 8 x 8 high-density grid imbedded with stainless steel electrodes 0.3 cm in diameter separated by 0.5 cm (PMT Electrodes (Chanhassen, Minnesota USA). Motor and speech mapping was performed using the Ojemann cortical stimulator (Integra Lifesciences) delivered biphasic square-wave pulses at 50 Hz, 0.5 usec, with incremental increases in stimulus intensity to 10 mA.  Endpoints were reproduction of symptoms, maximum current intensity, or the presence of an after-discharge. At least 2 trials were performed at each site. Patient demographics, reason for surgery, presence of seizures and epileptiform discharges, and hospital course were examined. Results: Thirty-four patients (18 Males) age 18-79 underwent awake craniotomy for resection of a brain lesion. A primary brain tumor was identified in all but 5 (encephalomalacia, meningioma, non specific gliosis, non-neoplastic lesion, hemorrhagic lesion).  The left temporal lobe was the most common site of HD-ECoG and ECS for functional mapping. Twenty patients (58.8%) presented preoperatively with epilepsy/seizures alone (n= 5) or seizures related to a brain tumor (n=14).  Twelve patients (35.2%) presented with symptoms related to a brain tumor alone prompting surgery. One patient (2.9%) presented with Dizziness and one patient (2.9%) presented with intracranial hemorrhage at tumor diagnosis.Twenty-four patients underwent awake craniotomy with the utilization of the intraoperative HD-ECoG.  Intraoperative epileptiform discharges were identified in 16 (67%)patients (lateralized periodic discharges in 4). Discharges were restricted from two to six contacts in the majority (spatial distribution 1-3 cm). Four (17%) had epileptiform discharges on scalp EEG though were otherwise normal in four patients. One patient experienced a prolonged intraoperative focal motor seizure during ECS in the absence of HD-ECoG.Post-operatively, 16/24 (66.7%) patients showed improvement (8 patients worsened/remained unchanged). Nine patients underwent awake surgery without the use of HD-ECoG, 5 (55.6%) patients experienced postoperative improvement, and four remained unchanged/worsened. Out of our cohort of 34 patients undergoing awake craniotomy, 4 patients (11.7%) experienced postoperative complications including infection, pulmonary embolism, diplopia and persistent focal seizures. Conclusions: HD-ECoG led to 89% of patients to remain seizure free post-operatively following tailored resection in eloquent cortex. Our study suggests intraoperative HD-ECoG may aid tailored resection in eloquent cortex by providing greater resolution to increase the extent of resection and preserve functional tissue Funding: no funding recieved