Intra-operative monitoring as an adjuvant to standard vagus nerve stimulation implantation.

PURPOSE: The treatment of refractory epilepsy by vagus nerve stimulation (VNS) is a well-established therapy. Complications following VNS insertion may be procedure-related or stimulation-related. Herein, we describe our technique of intra-operative neuro-monitoring (IONM) in an attempt to diminish these adverse events. METHODS: This retrospective study describes 66 consecutive patients between the ages of 3 and 12 years who had undergone primary VNS implantation. The study population consisted of two cohorts, one in which the VNS device was implanted according to the standard described technique and a second group in which IONM was used as an adjuvant during the VNS device placement. Prior to VNS insertion, a Pediatric Voice Handicap Index (PVHI) was performed to assess voice-related quality of life, and this was repeated at 3 months following VNS insertion. RESULTS: Sixty-six patients underwent the VNS implantation. Forty-three patients had a "standard" VNS insertion technique performed, whereas 23 had IONM performed during the VNS implantation. There were significant changes in the PVHI scores across both cohorts at 3-month follow-up. There were no statistically significant differences in PVHI scores between the monitored group and non-monitored group at 3-month follow up. CONCLUSIONS: IONM can be used during VNS insertions to ensure correct placement of the leads on CNX. IONM may minimise vocal cord stimulation by placing the lead coils on the area of nerve eliciting the least amount of vocal cord EMG response. IONM however does not appear to improve voice outcomes at early follow up.

Use of intra-operative stimulation of brainstem lesion target sites for frameless stereotactic biopsies.

INTRODUCTION: Frameless stereotactic navigation is used to direct the trajectory and biopsy site of target lesions. We report on a novel intra-operative stimulating (IOS) probe that is integrated into a commercially available stereotactic biopsy needle with the rationale that stimulation of the intended biopsy site should predict functional tissue thus preventing inadvertent biopsy of eloquent tissue. METHODS: Patients undergoing brainstem biopsies for atypical lesions were offered the additional stimulation procedure. The IOS probe was used to deliver stimulation in an attempt to determine the proximity of eloquent tissue. Once the desired location of the biopsy needle was achieved, the IOS probe was inserted down the centre of the biopsy needle and the stimulus applied. If no action potential was recorded, biopsies from four quadrants of the lesion were taken. If however a compound action potential was recorded, a new target was selected. RESULTS: Nine patients had the biopsy and stimulation procedure performed. The median age was 36 months. A minimum of 8 samples were obtained from each patient. Biopsy material was adequate to obtain a diagnosis in all 9 patients. In 2 cases use of the device influenced the insertion trajectory or biopsy site. No patients experienced any complications directly attributable to either the biopsy procedure or application of the stimulation. CONCLUSIONS: Use of the IOS probe for intra-operative stimulation of the intended brainstem biopsy site was found to be safe and feasible. The addition of stimulation using the IOS probe can be done with minimal change in workflow.