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Where is the Pudendal Nerve?

As found in my blog, How to Diagnose and Treat Pudendal Neuralgia, “The Pudendal nerve is the lower section of a series of nerves that comes from the lower back and sacrum called the Sacral Plexus.  The Pudendal nerve comes out of the S2-5 area, goes under the Piriformis muscle, leaves the pelvis through the greater sciatic foramen, back to the lessor sciatic foramen, over the sacrospinous ligament, and under the sacrotuberous ligament. Anywhere along the path, from the lower back and sacral area to the ending of the pudendal nerve (vagina/pelvis, anus, and perineum), this nerve can be pressured on, compressed, irritated, and entrapped causing symptoms that lead to the diagnosis of Pudendal Neuralgia.”

Diagram of the lower spine and its nerves

Sacral Plexus: courtesy of teachmeanatomy.info

Who Performs Pudendal Nerve Block and How Is It Performed?

Physiatrists (physical medicine and rehab. physicians), radiologists, anesthesiologists, neurologists, and surgeons are the common physicians that perform pudendal nerve blocks. According to the National Library of Medicine, there are 3 approaches to blocking the pudendal nerve: transvaginal, transperineal, and perirectal.

Transvaginal Approach

“The transvaginal approach to pudendal nerve block is a common approach for obstetric procedures. The female patient positioning is in the lithotomy position. Through the lateral vaginal wall, the clinician will identify the ischial spine. Through a long injection needle with a guide, the sacrospinous ligament gets punctured, and the needle is passed 1 cm caudal from the ischial spine until noticing a loss of resistance. Using a needle guide such as the Iowa Trumpet is recommended to limit the depth of penetration and minimize tissue injury. Upon negative aspiration, the local anesthetic is injected posteriorly to the ischial spine at the attachment of the sacrospinous ligament. The injection can also be performed medial to the ischial spine to minimize the risk of anatomical damage. Pinprick test in the anogenital area is performed to assure adequate anesthesia in the region.

Transperineal Approach

The other method is the transperineal approach. This method is also useful in anorectal and urological procedures. The male or female patient will be placed in the lithotomy position. After identifying the ischial spine, the needle will puncture the skin transperineally, medial to the ischial tuberosity. The needle is advanced in the posterolateral direction until it touches the ischial spine. The needle is then advanced through the sacrospinous ligament and 1 cm in the medial inferior direction to the ischial spine. After negative aspiration, the local anesthetic of choice is injected.

Perirectal Approach

A pudendal nerve block can also be performed via a perirectal approach using a nerve stimulator to elicit contractions of the external anal sphincter. Patient positioning is recumbent. The clinician’s index finger will be inserted into the anus to palpate the ischial spine. The needle is advanced lateral to the rectum towards the ischial spine. Similar to the other methods, the needle is advanced 1 cm inferior and medial to the attachment of the sacrospinous ligament to the ischial spine. After negative aspiration, the local anesthetic of choice is injected.

The effect of the block is usually immediate. Depending on the clinical symptoms and type of procedure, a pudendal nerve block is either unilaterally or bilaterally. PNB can take place with or without ultrasound guidance in females. However, in male patients, PNB is typically performed using ultrasound guidance due to challenges in identifying the anatomical landmarks. PNB under MRI, fluoroscopy, or CT guidance have also been described, but are less common methods.”

Must Know Facts About Pudendal Nerve Block

  • Most patients have reduced pain lasting 2-4 months. Some patients can get relief lasting greater than a year.
  • You will go home soon after your nerve block. Someone needs to drive you home because you may have numbness and, depending on the injection location, you may have difficulty walking for a few hours.
  • Side effects of the procedure include damage to the nerve or surrounding structures, allergic reaction to medications, lack of pain relief, bleeding, infection, risk of temporary numbness in the leg following this procedure (due to medications spreading to the sciatic nerve), and soreness after the procedure.
  • Once the procedure is performed, you should still see a pelvic floor therapist (physical therapist or another health care provider that specializes in pelvic floor therapy) to work on the internal and external pelvic floor muscles to bring balance and fine tone.

Remember while a Pudendal nerve block may ease the pain, it will not fix the pelvic imbalance. All pelvic floor dysfunctions require the balancing of the pelvis, the “house” that the pelvic floor is the “floor” of.

If you have any questions about pelvic floor dysfunction, contact me.

Dr. Shakib