Assistant Professor Neurology/Epilepsy University of North Carolina at Chapel Hill
Rationale: SEEG is a tridimensional invasive exploration study of the epileptic network based on presurgical clinical and anatomic-electrical correlations aimed to facilitate tailored surgeries (1). Every implanted electrode represents a specific question and must be externally identified and secured typically with an anchor bolt.1,2 Bone thickness of less than 2 mm is a relative contraindication to SEEG.3 However, what happens when there is little to no bone over sites that are crucial for the epileptic network? Methods: Case PresentationA 72-year-old woman with a 30-year history of epilepsy, a right frontal astrocytoma status post multiple craniotomies, and radiation treatments. She had done well with no recurrence on serial brain MRIs or seizures on two AEDS. The patient was admitted after a convulsive seizure that progressed to status epilepticus. EEG showed electroclinical seizures in the right frontocentral regions associated with left upper extremity movements, aphasia, w/wo impaired awareness. Despite a thorough evaluation, no etiology was found. Multiple AEDS were used to control her seizures resulting in significant sedation, changes of which resulted in frequent seizures. Epilepsy surgery with a standard frame-based SEEG was recommended. When limited bone was encountered (Figure 1A), skin and soft tissue were penetrated down to the dura. A slotted cannula was passed to the appropriate target. SEEG electrodes were passed through the cannulas, and then the later removed. Electrodes were individually secured to the scalp with 4-0 Nurolon suture. The bundle of electrodes was then also secured to the scalp with 2-0 Nurolon suture (Figure 1B, C). Results: Eleven SEEG electrodes were placed and stabilized with bolts, while five with cannulas and sutures. The trajectories of all electrodes were confirmed by CT head (Figure 1D). We did not have CSF leak, and all electrodes remained in place over seven days of monitoring. Seizures were recorded, including electrodes that were sutured (Figure 2), allowing for resection of seizure onset zones allowing for reduction of seizure medications without recurrence of seizures.Two techniques for placing SEEG leads have been studied in cadaveric humans (4), described as "technique 1" electrodes (applying to guide bolts and external stylets) and 13 "technique 2" electrodes (without guiding bolts and external stylets)" (4). Technique 2 was reported to be less accurate from entry to target, especially with oblique approaches and distances of > 50 mm. The rate of SEEG electrode mispositioning is 0.4% (5). The SEEG electrodes where bone was limited in our case were placed with a variant of technique 2 including oblique and orthogonal trajectories with recording depths varying from 23.7 mm to 59.6 mm. Trajectories, in our case, were within expected locations, and electrodes remained secured throughout the monitoring.SEEG electrode placement with cranially fixed guide bolts and stabilization has been recognized as the most accurate implant strategy. However, this case raises the possibility of other techniques that could be safely implemented when there are limitations with the "gold standard." Conclusions: We were able to safely and effectively place SEEG electrodes without cranially fixed guide bolts. Also, electrodes were secured throughout the monitoring enabling monitoring of cortical regions that were crucial to the epileptic network and resective surgery. This case suggests the possibility of a safe and effective alternative method for SEEG electrode implantation, especially when bone limitations exist; however, future follow up studies may clarify these findings.
References 1. Isnard J, etal Neurophysiol Clin. 2018;48(1):5-13 2. Gonzalez-Martinez, etal JNS, 120(3), 639-644 3. Minotti L, etal Neur Funding: Please list any funding that was received in support of this abstract.: None Click here to view image/table