Pudendal nerve entrapment at the level of sacrospinous ligament or Alcock's canal; laparoscopic management.

The pudendal nerve is formed by the spinal roots at levels S2–S4. It is a motor, autonomic, and sensory nerve responsible for sensitivity in the perianal and genital regions, as well as motor innervation of the anal and bladder sphincters. It passes through the pelvis parallel to the pudendal vein and arteries. This nerve exits the pelvis between the sacrospinous and sacrotuberous ligaments and then passes through Alcock’s canal. The pudendal nerve gives rise to the inferior rectal, perineal, and dorsal nerves of the penis and the clitoris. The mechanical compression of the pudendal nerve is often referred to as entrapment. Entrapments may be caused by pelvic floor muscle spasm, pressure from surrounding ligaments (sacrospinous, sacrotuberous), or scar tissue from trauma or surgeries involving the surrounding areas; other causes may include endometriosis, vascular compression, and tumors [ 1 – 3 ]. Pudendal nerve entrapment syndrome is characterized by unilateral or bilateral neuropathic pain in the pudendal nerve and is caused by compression of the nerve at different levels along its course. The pudendal nerve can be compressed at four different levels: below the piriformis muscle, at the level of the sacrospinous ligament, when the nerve is trapped between the sacrospinous and sacrotuberous ligaments, in Alcock’s canal, and at the level of terminal branches [ 4 , 5 ]. The Nantes criteria, which have been proposed for diagnosing pudendal nerve entrapment syndrome, a cause of pudendal neuralgia, are the presence of the four essential clinical diagnostic criteria (pain in the territory of the pudendal nerve, worsened by sitting, the patient is not awoken at night due to pain, and no objective sensory loss). A diagnostic anesthetic pudendal nerve block should be performed and a positive block strongly supports these elements of clinical suspicion (5th criterion) [ 6 ]. However, the question remains whether it is clinically possible to distinguish pudendal nerve entrapment at the level of the sacrospinous ligament from entrapment at Alcock’s canal. The Nantes criteria were mainly developed to diagnose entrapments at the level of Alcock’s canal and/or the interligamentous plane [ 6 ]. Determining the level of compression is of paramount significance for correct diagnosis and management. In cases in which conservative treatments fail, laparoscopic pudendal nerve release should be the surgical treatment of choice over traditional treatments (transgluteal, transperineal, transvaginal, or transischiorectal) because the laparoscopic approach has several advantages [ 5 ].

A 38-year-old woman with gravid 9, parity 4 (G9P4) underwent four cesarean deliveries (in-years-2006, 2008,2016, and 2018), complaining of pain while sitting. She had pain from the clitoris to the anus on the left side for 2 years since 2023, and her pain score was 8/10, according to the visual analog scale. Transvaginal ultrasonography revealed pain over the left sacrospinous ligament upon palpation and Tinel’s sign (+). Left pudendal nerve block with 5 mL of 0.5% Bupivacaine relieved pain for approximately 2 hours. Our patient met all five Nantes criteria and developed pudendal neuralgia due to pudendal nerve entrapment. She had been taking medications for pain such as amitriptyline, gabapentin, and pregabalin. She also underwent physiotherapy for pain. However, the pain remained refractory for 1 year. Subsequently, laparoscopic pudendal nerve release was planned. She had a history of anal fissure (in 2012) and hemorrhoid (in 2010) operations, as well as a total laparoscopic hysterectomy and bilateral salpingectomy operation (in 2021). Under general anesthesia, the patient was placed in the modified Lloyd-Davies position. Four trocars were used to perform the procedure. A 30-degree optic was used. Laparoscopic approach for left pudendal nerve release started dissection at the level of the medial to the infundibulopelvic ligament. After visualization of the ureter, obliterated umbilical artery, and obturator nerve and vessels, dissection continued deeper till to the pelvic floor visualizing the obturator internus muscle and arcus tendineus levator ani ( Fig. 1 ). While dissection was being performed, the first sciatic nerve was recognized, then the pudendal nerve and vessels were identified, and the coccygeus muscle and sacrospinous ligament were observed. The sacrospinous ligament was partially cut, and the pudendal nerve was released adjacent to the ischial spine, after which Alcock’s canal was opened proximally, starting from the ischial spine where the arcus tendineus levator ani was attached. The total operation time was 60 minutes and the estimated blood loss was minimal. No intra-operative complications were observed. The postoperative care was uneventful and the patient was discharged on 1 day after the surgery without any serious complaints. The pain decreased on her postoperative examination. After 1 month, her pain score decreased to 3/10 on the visual analog scale. Follow-up visits will be continued at 3 months and 6 months and then every 6 months.

Intraoperatively, scar tissue from trauma or surgeries involving the surrounding areas, or other causes including endometriosis, vascular compression, and tumors, were not detected; therefore, the most probable causes were pressure from the surrounding ligaments (sacrospinous, sacrotuberous) and pressure at the Alcock’s canal. Owing to uncertainty, the decision was made to dissect Alcock’s canal and release the pudendal nerve in Alcock’s canal, in addition to releasing the nerve at the sacrospinous ligament level. There are two reasons for dissecting Alcock’s canal and releasing the pudendal nerve in Alcock’s canal in addition to releasing the pudendal nerve at the sacrospinous ligament level. First, as mentioned above, the Nantes criteria do not distinguish entrapment at the level of the sacrospinous ligament from entrapment at Alcock’s canal [ 6 ]. The other reason is variation in pudendal nerve course at the sacrospinous ligament level and at the entrance, throughout, and exit of the Alcock’s canal among individuals and even within individuals on the left and right sides [ 7 ]. In conclusion, it is clinically difficult to discriminate pudendal nerve entrapment at the level of the sacrospinous ligament from Alcock’s canal, because the Nantes criteria may not discriminate entrapment at the level of the sacrospinous ligament from Alcock’s canal. Therefore, if pudendal neuralgia due to pudendal nerve entrapment is diagnosed according to the Nantes criteria and if conservative treatments fail and laparoscopic pudendal nerve release is planned, combined decompression at the sacrospinous ligament and Alcock’s canal may be considered when no obvious cause is identified pre- and intraoperatively to avoid the potential risk of incomplete decompression. Further studies with larger cohorts and longer follow-up periods are needed to confirm the efficacy of this approach.