eP485 - The Utility of Postoperative MRI to Evaluate SNS Efficacy

Purpose/Background: Sacral nerve stimulation (SNS) showed to be an effective therapy in patients with fecal incontinence (FI). Although an accurate electrode placement, success rate may decrease over time and further SNS settings reprogramming are needed. Furthermore, adverse events related to electrical stimulation may occur. Recently, MRI-compatible SNS have been introduced. The aim of this study was to assess the utility of MRI in patient’s evaluation after SNS implant.Methods/Interventions: This is a prospective observational study on subsequent patients who underwent MRI-compatible SNS definitive implant, at a tertiary academic center, for FI from December 2022 to June 2023. During the follow up period, they routinely underwent a 3-months postoperative MRI assessment with a specific protocol. SNS implant was performed in local anesthesia using a standardized technique under the guidance of intraoperative X-ray imaging and sensory/motor responses. Baseline patients’ characteristics, SNS parameters, intra- and postoperative complications, FI episodes and CCFI score were collected. Radiological data were assessed by a well-trained radiologist.Results/Outcomes: 5 patients (4 female, 80%) who underwent MRI-compatible SNS implant were included. At 3-months follow up, a reduction in mean FI episodes (6.2 vs. 3.0, p=0.068) and CCFI score (11.4 vs. 7.0, p=0.042) was reported in all patients. After performing MRI, an explant of the SNS system was necessary due to infection. Although a standardized placement technique was adopted and SNS was effective in all patients, only 2 electrodes were detected in the correct position at MRI assessment. One electrode was placed too medial to the sacral nerve root, in the mesorectal plane (Figure 1). Moreover, a displacement of the tined lead electrode was identified in two patients reporting an efficacy reduction during the last month, even if the electrode resulted in the close proximity of the target sacral spine nerve (Figure 2). Therefore, in these patients, a SNS settings reprogramming was needed in these patients on the base of MRI findings.Conclusion/

Discussion: A systematic postoperative MRI assessment could be able to explain a suboptimal or lack of function of the SNS implant, and guide clinicians for reprogramming SNS parameters. Deep foci of infection could also be identified. Further technical and settings adjustments should be adopted to increase the SNS efficacy."Figure 1

The electrode (white arrow) was placed too medial to the sacral nerve root, in the mesorectal plane (the dotted white line indicates the ideal position of the tined lead electrode).
Figure 2

Although the electrode was placed in the close proximity of the target sacral spine nerve (the dotted white arrow indicates the distal end of the electrode), a displacement of the tined lead electrode was detected (white arrow) in sagittal (a) and axial (b) views."