Evaluation of two-dimensional intraoperative neuromonitoring for predicting urinary and anorectal function after rectal cancer surgery

Purpose: The aim of this study was to compare the results of two-dimensional intraoperative neuromonitoring (IONM) with the postoperative urinary and anorectal function of rectal cancer patients. Methods: A consecutive series of 35 patients undergoing low anterior resection were investigated prospectively. IONM was performed with electric stimulations of the pelvic splanchnic nerves under simultaneous manometry of the bladder and electromyography (EMG) of the internal anal sphincter (IAS). Urinary and anorectal function were evaluated preoperatively and at follow-up by standardized questionnaires, digital rectal examination scoring system, and long-term catheterization rate. Results: The rate of postoperative newly developed bladder dysfunction was 17 %. IONM with bladder manometry had a sensitivity of 100 %, specificity of 96 %, positive predictive value of 83 %, negative predictive value of 100 %, and overall accuracy of 97 %, respectively. The proportion of patients with severely impaired anorectal function at follow-up was 8 %. The sensitivity, specificity, and positive and negative predictive values for IONM with EMG of the IAS were, respectively, 100, 96, 67, and 100 % with an accuracy of 96 %. The degree of agreement for IONM with EMG of the IAS was good for anorectal function (k = 0.780) and poor for urinary function (k = 0.119). IONM with bladder manometry yielded a very good degree of agreement for urinary function (k = 0.891) and a fair agreement for anorectal function (k = 0.336). Conclusions: The two-dimensional IONM method is suitable for verification of bladder and IAS innervation. Accurate prediction of urinary and anorectal function necessitates both bladder manometry and EMG of the IAS.