Tethered cord release in patients after open fetal myelomeningocele closure: intraoperative neuromonitoring data and patient outcomes.

Purpose: The purpose of the study was to better understand the clinical course and impact of tethered cord release surgery on patients who have previously undergone open spinal dysraphism closure in utero.

Methods: This is a single-center retrospective observational study on patients undergoing tethered cord release after having previously had open fetal myelomeningocele (MMC) closure. All patients underwent tethered cord release surgery with a single neurosurgeon. A detailed analysis of the patients' preoperative presentation, intraoperative neuromonitoring (IONM) data, and postoperative course was performed.

Results: From 2009 to 2021, 51 patients who had previously undergone fetal MMC closure had tethered cord release surgery performed. On both preoperative and postoperative manual motor testing, patients were found to have on average 2 levels better than would be expected from the determined anatomic level from fetal imaging. The electrophysiologic functional level was found on average to be 2.5 levels better than the anatomical fetal level. Postoperative motor levels when tested on average at 4 months were largely unchanged when compared to preoperative levels. Unlike the motor signals, 46 (90%) of patients had unreliable or undetectable lower extremity somatosensory evoked potentials (SSEPs) prior to the tethered cord release.

Conclusion: Tethered cord surgery can be safely performed in patients after open fetal MMC closure without clinical decline in manual motor testing. Patients often have functional nerve roots below the anatomic level. Sensory function appears to be more severely affected in patients leading to a consistent motor-sensory imbalance.