Intraoperative Monitoring of Sacral Root Function

Objective: There is an increasing demand for real-time functional feedback of surgery involving the cauda equine, conus medullaris, and sacral roots. Therefore, intraoperative monitoring (IOM) of the bulbous cavernous reflex (BCR) to monitor the S2–S4 reflex arc has been introduced be Deletis et al in 1997. Yet, until now no systematic correlation to postoperative outcome has been performed. The goal of this study was to investigate the feasibility and the predictive value of the BCR in a consecutive cohort of patients. Methods: The BCR was performed in 19 patients undergoing surgery (2009–2014) under total intravenous anesthesia. BCR was elicited by electrical stimulation of the dorsal penile/clitoral nerve and recorded in the external anal sphincter muscle. A short train of five to seven pulses with 0.5 ms pulse duration and 4 ms interstimulus interval was applied using a 1 Hz repetition rate. This series included five ependymoma, four lipoma, three paraganglioma, three vascular malformations, and four other pathologies. Results: The BCR was successfully obtained at baseline in 15 patients; in two patients there were technical limitations and in two patients the BCR was not evocable. Sudden loss or significant threshold increment was observed in two patients. Both of them presented postoperative urinary tract and sphincter dysfunction. Reversible fluctuations were observed in three patients, all of them presented an unchanged neurological outcome. A stable BCR could be monitored in 10 patients and all of them had no postoperative dysfunction. Conclusions: IOM of the BCR is a feasible and reliable tool to predict postoperative sacral root function.