Refractory chronic pelvic pain caused by pudendal nerve entrapment is a complex and diagnostically challenging condition. Although MR tractography can be employed for diagnosis, interpretation largely relies on comparative analysis between the left and right sides, making it difficult to determine whether the neuropathy is in the acute or chronic stage. If nerve block interventions is ineffective, decompression surgery becomes necessary[1], but its success can only be assessed post-operatively, without the benefit of precise intraoperative predictions.

We present a case of a 40-year-old man suffering from refractory chronic pelvic pain for 15 years. After failing to respond to oral medications, pelvic floor rehabilitation, and ultrasound-guided nerve block treatment, the patient underwent an magnetic resonance tractography. His diffusion tensor imaging revealed significant swelling of the left pudendal nerve near the level of ischial spine, suggesting left pudendal entrapment. However, the patient reported initial pain starting on the right side of the perineum, which later evolved to affect both sides. Consequently, the plan included intraoperative neuromonitoring (IOM) during surgery to confirm the diagnosis and assist in deciding whether bilateral or unilateral pudendal neurolysis should be performed[2].

Following anesthesia, placement of IOM devices was initiated, including skin patches on the head and penis, needle probes in the thigh and anal sphincter, and an intraurethral sensor on the Foley catheter. Subsequently, robotic surgery was applied to approach the bilateral pudendal nerves. Before performing the sacrospinal ligament incision, evaluations such as pudendal somatosensory evoked potential, bulbocavernosus reflex, and electromyography including bulbocavernosus muscles, thigh adductor, and external anal sphincter were conducted in free scanning and stimulated modes using a laparoscopic stimulation probe. This measurement was to evaluate the patient’s motor and sensory functions. It was observed that overall pudendal neuropathy and motor dysfunction were more severe on the left side, whereas sensory dysfunction was notably more intense on the right side. Preliminary assessments indicated bilateral pudendal neuropathy, with the left side presenting as acute injury and the right side as chronic phase. After bilateral pudendal neurolysis, significant improvement in nerve signals was observed on the left side, with only partial improvement on the right side.

IOM could serve as a crucial adjunct tool for pudendal nerve entrapment, offering valuable insights in both confirming the diagnosis and assessing nerve recovery.

Int Neurourol J. 2024 Mar;28(1):11-21.
J Clin Neurophysiol. 2014 Aug;31(4):323-5.