Pudendal Nerve Blocks

Anatomical Overview¹

Pudendal Nerve Course

• The pudendal nerve arises from the ventral rami of the second, third, and fourth sacral spinal nerves (S2–S4). It exits the pelvis through the greater sciatic foramen, most often passing medially to the ischial spine and posterior to the sacrospinous ligament. This anatomical relationship is clinically important and serves as a key landmark for pudendal nerve block procedures.
• After exiting the pelvis, the pudendal nerve travels ventrally in the interligamentous plane between the sacrospinous and sacrotuberous ligaments at the level of the ischial spine. This is a common site for entrapment and clinical symptoms. Entrapment at this location is observed in the majority of patients with pudendal neuralgia.²

• The nerve then enters Alcock’s canal (pudendal canal), a fascial tunnel formed by the obturator internus muscle, where it travels alongside the internal pudendal artery and vein. Within the canal, the pudendal nerve is arranged inferolaterally to the vessels and gives off branches, including the muscular branch to the urogenital triangle.
• Substantial anatomical variation exists in the number and branching patterns of pudendal nerve trunks. Although a single trunk is most commonly observed, two or three trunks may be present in a notable proportion of cases. Additionally, the inferior rectal nerve may arise independently or traverse the sacrospinous ligament, a variation that can increase the risk of nerve entrapment.³
• Distally, the pudendal nerve divides into its terminal branches: the inferior rectal nerve, the perineal nerve, and the dorsal nerve of the penis or clitoris. The branching may occur before or within Alcock’s canal, and the nerve is susceptible to compression at several points along its course, including the urogenital diaphragm and the base of the penis.
• Understanding these anatomical details is essential for effective diagnosis, nerve block placement, and surgical management of pudendal neuralgia and related pelvic pain syndromes.

Nerve Block Techniques

Overview

• Pudendal nerve blocks can be performed via several approaches, including transgluteal, transperineal, transvaginal, and pararectal. The choice of approach depends on patient anatomy and the specific clinical indication.
• Image-guided ultrasonography, computed tomography (CT), or fluoroscopy can be used for a pudendal nerve block. These imaging modalities are commonly used to improve accuracy and safety.

Ultrasound-Guided

• Ultrasound-guided techniques allow real-time visualization of anatomical landmarks and the spread of anesthetic, with high accuracy at both the ischial spine and Alcock’s canal levels. CT and fluoroscopy guidance are also effective, particularly for targeting the nerve in complex cases or when anatomical variation is suspected.⁴
• Objective: Provide local anesthesia to the entire sensory and motor territory supplied by the pudendal nerve before it branches. This includes the perineum, external genitalia (penis or clitoris), perianal skin, lower third of the vagina in females, and the external anal and urethral sphincters.⁴
• Common Indications: Diagnostic and therapeutic management of pudendal neuralgia and chronic pelvic pain, perioperative and postoperative analgesia for perineal and anorectal procedures, and vulvar biopsies.
• Probe placement: Place the patient in the prone position. Begin with the probe in the transverse plane over the posterior superior iliac spine, then scan inferolaterally toward the deep gluteal region to identify the ischial spine.⁵
• Key features to confirm the ischial spine level include:
  • Visualization of the ischial spine as a distinct, pointed bony structure.
  • Identification of the interligamentous plane, which appears as a thin hyperechoic band attached to the ischial spine.
  • Detection of the internal pudendal artery using color Doppler. The artery typically runs just lateral to the pudendal nerve and adjacent to the ischial spine.
  • In many cases, the pudendal nerve itself may be seen as a small, oval hypoechoic structure medial to the artery and close to the ischial spine.

Transvaginal Approach

• Preoperative transvaginal pudendal nerve block contributes to multimodal pain management by providing targeted analgesia that reduces postoperative pain and decreases the need for additional analgesics, thereby improving patient comfort and recovery after vaginal tear repair and pelvic reconstructive procedures.⁷
• Objective: Provide local anesthesia to the perineal region, including the vulva, lower vagina, perineal skin, and the perianal area.
• Common Indications: Analgesia for the second stage of labor, repair of an episiotomy or perineal laceration, and minor surgeries of the lower vagina and perineum
• The transvaginal approach is performed with the patient in the lithotomy position. The ischial spine is then palpated along the posterolateral vaginal sidewall. A needle guide is placed on the sacrospinous ligament just inferior and medial to the ischial spine, and the needle is advanced to the attachment of the sacrospinous ligament to the ischial spine for injection of local anesthetic.⁷

Transgluteal Approach

• The transgluteal approach is most commonly performed under fluoroscopic guidance, targeting the pudendal nerve near the ischial spine and sacrospinous ligament. This technique allows precise needle placement and anesthetic delivery to the main trunk of the pudendal nerve.⁸
• Objective: Provide both diagnostic confirmation and therapeutic pain relief for patients with pudendal neuralgia, particularly when conservative treatments have failed.
• Common Indications: management of pudendal neuralgia, and chronic perineal or pelvic pain that is refractory to conservative treatments.
• The patient is positioned prone. After identifying the ischial spine using fluoroscopy, a needle is advanced through the gluteal muscles toward the ischial spine, just medial to the sacrospinous ligament. Once the needle tip is confirmed at the target site, aspiration is performed to avoid intravascular injection, and then local anesthetic is injected around the pudendal nerve.⁸

Lithotomy Approach (Dorsal Lithotomy Position in Pediatric Patients)

• Patients are placed in the lithotomy position (supine with hips and knees flexed, legs supported in stirrups). In infants and smaller children, the dorsal lithotomy or “frog-leg” position (supine with hips flexed and abducted) is preferred, as it provides optimal access to the perineum and ischial spine.^9,10
• A linear ultrasound probe is commonly used to approach the pudendal nerve via the ischiorectal fossa to identify key landmarks, such as the ischial spine, sacrospinous ligament, and pudendal canal, thereby ensuring accurate needle placement and reducing complications.¹¹
• Common Indications include perineal and urological procedures, including urethroplasty, hypospadias repair, and circumcision.
• Ultrasound-guided pudendal nerve blocks in pediatric urologic patients provide superior analgesia and safety compared to traditional caudal blocks, resulting in better pain scores, fewer complications, and reduced risk of structural injury or motor blockade, making them an effective option for pediatric urological procedures.9,10

Benefits, Risks, and Limitations

Benefits

• Pudendal nerve blocks are highly effective for short-term pain relief in pudendal neuralgia and chronic pelvic pain, with nearly half of patients achieving at least 30% pain reduction at two weeks post-procedure, and many experiencing improvements in daily function and reduced medication use. These blocks can be performed quickly and safely in the outpatient setting, with a low complication rate and good tolerability.⁸

Risks

• Complications are uncommon but may include transient lower-limb paresthesia, bleeding, infection, and, rarely, injury to adjacent structures. Image-guided techniques (ultrasound, CT, fluoroscopy) minimize these risks by improving accuracy and avoiding vascular or nerve injury.⁴
• Most adverse effects are minor and reversible.

Limitations

• The duration of pain relief is often limited, with efficacy declining over months. Not all patients achieve complete pain relief, and the block may not anesthetize all pudendal nerve branches.
• The diagnostic value is imperfect, as incomplete anesthesia or pain relief does not exclude pudendal neuralgia. Repeated blocks may be needed, and if relief is only temporary, surgical decompression or other interventions may be considered.⁴