The impact of sub specialization within functional neurosurgery on patient outcomes in a comprehensive epilepsy center.

BACKGROUND: One in three patients with epilepsy are medication-refractory and may benefit from investigations and operative treatment at a comprehensive epilepsy center. However, while these centers have capabilities for advanced seizure monitoring and surgical intervention, they are not required to have a functional neurosurgeon who is primarily focused in epilepsy surgery. Therefore, the objective of this study is to determine the impact of having a sub-specialized, epilepsy-focused functional neurosurgeon on patient outcomes. METHODS: We conducted a retrospective chart review for all patients who underwent surgical intervention for medically refractory epilepsy at a Level 4 comprehensive Epilepsy Center from 2008 through 2019. Data was divided into two groups: group 1 comprised patients who had surgery before the hiring of a dedicated epilepsy-focused functional neurosurgeon in 2016, and group 2 was afterwards. We compared surgical procedures, significant complications, and seizure outcomes. RESULTS: A total of 101 patients underwent 105 operations (52 in group 1 and 53 in group 2), not including intracranial EEG insertion. Compared to group 1, group 2 had more surgeries performed per year (15.1 vs. 6.5), and a significantly lower Engel score at last follow-up (1.78 vs. 2.57; p < 0.001). There was no difference in percentage of cases undergoing iEEG, and no difference in complication rates. CONCLUSIONS: In this series, the hiring of a sub-specialized functional neurosurgeon dedicated to epilepsy surgery in a comprehensive epilepsy center was associated with an increase in surgical volume and improved seizure outcomes.

Superior accuracy and precision of SEEG electrode insertion with frame-based vs. frameless stereotaxy methods.

BACKGROUND: Stereotactic electroencephalography (SEEG) has largely become the preferred method for intracranial seizure localization in epileptic patients due to its low morbidity and minimally invasive approach. While robotic placement is gaining popularity, many centers continue to use manual frame-based and frameless methods for electrode insertion. However, it is unclear how these methods compare in regard to accuracy, precision, and safety. Here, we aim to compare frame-based insertion using a CRW frame (Integra®) and frameless insertion using the StealthStation™ S7 (Medtronic®) navigation system for common temporal SEEG targets. METHODS: We retrospectively examined electrode targets in SEEG patients that were implanted with either frame-based or frameless methods at a level 4 epilepsy center. We focused on two commonly used targets: amygdala and hippocampal head. Stealth station software was used to merge pre-operative MR with post-operative CT images for each patient, and coordinates for each electrode tip were calculated in relation to the midcommissural point. These were compared to predetermined ideal coordinates in regard to error and directional bias. RESULTS: A total of 81 SEEG electrodes were identified in 23 patients (40 amygdala and 41 hippocampal head). Eight of 45 electrodes (18%) placed with the frameless technique and 0 of 36 electrodes (0%) placed with the frame-based technique missed their target and were not clinically useful. The average Euclidean distance comparing actual to ideal electrode tip coordinates for frameless vs. frame-based techniques was 11.0 mm vs. 7.1 mm (p < 0.001) for the amygdala and 12.4 mm vs. 8.5 mm (p < 0.001) for the hippocampal head, respectively. There were no hemorrhages or clinical complications in either group. CONCLUSIONS: Based on this series, frame-based SEEG insertion is significantly more accurate and precise and results in more clinically useful electrode contacts, compared to frameless insertion using a navigation guidance system. This has important implications for centers not currently using robotic insertion.

Intraoperative computed tomography for intracranial electrode implantation surgery in medically refractory epilepsy.

OBJECT: Accurate placement of intracranial depth and subdural electrodes is important in evaluating patients with medically refractory epilepsy for possible resection. Confirming electrode locations on postoperative CT scans does not allow for immediate replacement of malpositioned electrodes, and thus revision surgery is required in select cases. Intraoperative CT (iCT) using the Medtronic O-arm device has been performed to detect electrode locations in deep brain stimulation surgery, but its application in epilepsy surgery has not been explored. In the present study, the authors describe their institutional experience in using the O-arm to facilitate accurate placement of intracranial electrodes for epilepsy monitoring. METHODS: In this retrospective study, the authors evaluated consecutive patients who had undergone subdural and/or depth electrode implantation for epilepsy monitoring between November 2010 and September 2012. The O-arm device is used to obtain iCT images, which are then merged with the preoperative planning MRI studies and reviewed by the surgical team to confirm final positioning. Minor modifications in patient positioning and operative field preparation are necessary to safely incorporate the O-arm device into routine intracranial electrode implantation surgery. The device does not obstruct surgeon access for bur hole or craniotomy surgery. Depth and subdural electrode locations are easily identified on iCT, which merge with MRI studies without difficulty, allowing the epilepsy surgical team to intraoperatively confirm lead locations. RESULTS: Depth and subdural electrodes were implanted in 10 consecutive patients by using routine surgical techniques together with preoperative stereotactic planning and intraoperative neuronavigation. No wound infections or other surgical complications occurred. In one patient, the hippocampal depth electrode was believed to be in a suboptimal position and was repositioned before final wound closure. Additionally, 4 strip electrodes were replaced due to suboptimal positioning. Postoperative CT scans did not differ from iCT studies in the first 3 patients in the series and thus were not obtained in the final 7 patients. Overall, operative time was extended by approximately 10-15 minutes for O-arm positioning, less than 1 minute for image acquisition, and approximately 10 minutes for image transfer, fusion, and intraoperative analysis (total time 21-26 minutes). CONCLUSIONS: The O-arm device can be easily incorporated into routine intracranial electrode implantation surgery in standard-sized operating rooms. The technique provides accurate 3D visualization of depth and subdural electrode contacts, and the intraoperative images can be easily merged with preoperative MRI studies to confirm lead positions before final wound closure. Intraoperative CT obviates the need for routine postoperative CT and has the potential to improve the accuracy of intracranial electroencephalography recordings and may reduce the necessity for revision surgery.

Dental hardware complicating diagnosis in refractory gelastic epilepsy secondary to hypothalamic hamartoma.

Hypothalamic hamartomas (HH) are developmental malformations of the hypothalamus associated with a potentially treatable epileptic encephalopathy, characterized by early onset gelastic seizures, the later development of multiple seizure types and progressive cognitive and behavioral decline. Surgical treatment of HH can lead to seizure control and improvement in the cognitive-behavioral syndrome. Video-EEG telemetry (VET) is often necessary to characterize the semiology of the seizures, but there are no specific interictal or ictal EEG pattems that will confirm the diagnosis. Magnetic resonance imaging (MRI) can identify HH and define their anatomy, but the imaging findings may be subtle and susceptible to artifactual contamination. We present a patient with intractable gelastic epilepsy in whom the diagnosis of HH was initially missed due to failure to recognize the clinical syndrome and contamination of the MRI images with dental hardware artifact. VET confirmed the clinical diagnosis and the HH was identified on MRI after the dental hardware was removed. VET should be performed to confirm seizure semiology in patients with suspected gelastic epilepsy. Establishing this diagnosis can subsequently direct the appropriate neuroradiological evaluation for HH and surgical treatment of these lesions.

Mechanisms of signal change during intraoperative somatosensory evoked potential monitoring of the spinal cord.

In scoliosis surgery, intraoperative somatosensory evoked potential (SSEP) monitoring has reduced the incidence of postoperative neurologic deficits. Many factors affect the amplitude and latency of SSEP waveforms during surgery. Somatosensory evoked potential amplitude decreases with ischemia and anoxia because of temporal dispersion of the afferent volley and conduction block in damaged axons. In conjunction with surgical manipulations, minor drops in blood pressure may result in substantial SSEP changes that reverse when perfusion pressure is increased. Irreversible anoxic injury to central nervous system white matter with loss of SSEP waveforms is dependent on calcium influx into the intracellular space. Somatosensory evoked potential monitoring may be less sensitive for detecting acute insults in the presence of preexisting white matter lesions. Increased extracellular potassium from acute baro-trauma can block axonal conduction transiently even when there is no axonal disruption. Marked temperature-related drops in SSEP amplitude may occur after exposure of the spine but before instrumentation and deformity correction. Hypothermia may increase false-negative outcomes. Short-interval double-pulse stimulation may improve the sensitivity of the SSEP in detecting early ischemic changes. For neurosurgical procedures on the spinal cord the use of SSEP monitoring in improving postoperative outcome is less well established.