Neurophysiological identification and differentiation between the motor and sensory roots in pediatric spinal cord lipoma surgery

Background: Radical resection of spinal cord lipomas reduces the rate of re-tethering. Current conventional neurophysiological mapping techniques are not able to differentiate between crucial motor nerve roots and sensory roots. Enhanced differentiation could contribute to complete resection. We present our experience with a double-train paradigm to differentiate between motor and sensory roots. Methods: In children undergoing spinal cord lipoma resection, the double-train mapping paradigm was used with an inter-train interval of 60 ms. Given the longer recovery time due to the H-reflex, a single muscle response was presumed to be elicited from a sensory root, and a double muscle response from a motor root. The primary endpoint was postoperative neurological outcome and bladder function at discharge. Results: We included 8 children undergoing 10 lipoma resections between 2016 and 2023. Double-train mapping was used in all cases. Motor and sensory roots were clearly differentiated in 6 cases and altered the course of surgery in 4 cases. Post-surgery, no sensory and motor function worsened within 3 months. Bladder function was stable in six and improved in two children. In two patients, bladder function worsened slightly at 3 months and 6 months, at which point one patient was re-operated on for re-tethering. Conclusion: Intraoperative mapping with the double-train paradigm reliably differentiated between motor and sensory nerve roots. Informing the surgeon on the specific function of a tethering root may help to maximize resection without risking major neurological deficits. Keywords: Intraoperative neurophysiology; Mapping; Nerve root stimulation; Reflex; Spinal cord lipoma.