Responsive nerve stimulation (RNS) represents a safe and effective treatment option for patients with medically refractory temporal lobe epilepsy. In cases of long intraparenchymal course and posterior-anterior electrode direction through occipital burr holes, disciplined stereotaxy is essential for stimulation of the appropriate target. A 13-year-old female with a history of multifocal, independent, bitemporal-onset seizures since 12 months of age showing evidence of left-sided mesial temporal sclerosis on MRI, underwent placement of bilateral mesial temporal RNS leads. An O-arm spin was performed after the placement and the images obtained were fused to the preoperative CT images. It demonstrated curvature of the leads, with some deviation from the planned trajectory, but no deviation from the target, that was worse on the left side, compared to the right; the left lead was placed first, followed by the right lead. Following discussion with our epilepsy neurology colleagues in the operating room, electrophysiological measurements from the implanted leads showed cleared epileptic activity and therefore no repositioning was pursued. Our hypothesis at that time was that cerebrospinal fluid leakage distorted the underlying ventricular anatomy causing some curvature in the lead during transventricular course and prolonged consideration during surgery. In conclusion, transventricular trajectories during RNS lead placement may lead to cerebrospinal fluid loss and associated lead deformation. The distal aspect of the lead may nonetheless reside in the desired surgical target. Neuromonitoring for epileptic signature can provide reassurance with regard to accurate lead placement, obviating the need for lead repositioning. Surgeons should also recognize that fused imaging may confuse inferred anatomic position from preoperative MRI with actual anatomy post brain shift.
Copyright © 2020, Kerezoudis et al.