A pudendal nerve block (PNB) is a regional anesthetic procedure involving the targeted injection of medication to provide temporary pain relief in the pelvic area. This technique is used either for anesthesia during certain medical procedures or as a diagnostic and therapeutic tool for managing chronic pain. The injection specifically targets the pudendal nerve, which is responsible for sensation and function in the lower pelvis and perineum. By temporarily interrupting the nerve signals, the block offers focused relief in areas difficult to treat with generalized pain medications.
The Role of the Pudendal Nerve
The pudendal nerve originates from the sacral plexus, drawing fibers from the second, third, and fourth sacral spinal nerves (S2-S4). This nerve travels through the pelvis before branching out to supply various structures. It provides sensory and motor function to the external genitalia, the skin around the anus, and the perineum.
The nerve’s path takes it near the ischial spine, a prominent bony structure that serves as a key landmark for administering the block. Its motor function controls the external urethral and anal sphincters, allowing for voluntary control over urination and defecation. Issues with the nerve’s wide-ranging sensory distribution can cause significant discomfort throughout the pelvic floor region.
Common Reasons for the Block
The pudendal nerve block serves both as regional anesthesia and as a treatment for persistent pain conditions. Historically, it has been a common technique to provide pain relief during the second stage of labor and delivery. It offers effective numbing for procedures like episiotomy repair, forceps-assisted delivery, or minor surgeries of the lower vagina and perineum.
For chronic pain, the block is primarily used to manage pudendal neuralgia, a condition characterized by persistent pain resulting from nerve compression or entrapment. The block is diagnostic: temporary relief after the injection confirms the pudendal nerve as the source of the pain.
The procedure is also employed for pain associated with anorectal surgeries, such as a hemorrhoidectomy, providing longer-lasting analgesia than superficial local anesthetics. Conditions like chronic vulvar pain (vulvodynia) or persistent rectal pain may also be treated with a PNB. The injection usually includes a local anesthetic for immediate relief and often a corticosteroid to reduce inflammation for a longer-term effect.
Specific Injection Sites and Techniques
The goal of the procedure is to deliver medication precisely where the pudendal nerve passes close to the ischial spine, before it branches out. This location, where the nerve wraps around the sacrospinous ligament, is the optimal target for blocking the main nerve trunk. Healthcare providers utilize two primary approaches to access this deep pelvic structure, often relying on imaging guidance.
The transvaginal approach is frequently used in obstetrics and gynecology, particularly during childbirth. The physician inserts a finger into the vagina to locate the ischial spine, a sharp bony protrusion on the side of the pelvis. A needle is then advanced through the vaginal wall, targeting the area just behind the sacrospinous ligament near the ischial spine.
For chronic pain management, a transgluteal or transperineal approach is often preferred, involving needle insertion through the skin of the buttock or the perineum. These approaches typically require imaging guidance, such as fluoroscopy (real-time X-ray) or ultrasound, to visualize the needle’s path and confirm its final position. Imaging guidance allows the provider to accurately place the medication at the nerve trunk or within Alcock’s canal.
In the transgluteal technique, the patient is positioned face-down, and the needle is guided toward the ischial spine from the buttock. Once the needle tip is confirmed adjacent to the nerve, the anesthetic solution is injected. The procedure is repeated on the opposite side if a bilateral block is required.
Patient Experience and Block Duration
Before the procedure, the injection site is cleaned, and a local anesthetic is administered to numb the skin, which may cause a brief stinging or burning sensation. During the actual nerve block injection, patients generally report feeling pressure rather than sharp pain as the needle is advanced toward the deep pelvic structures. The procedure typically takes only a few minutes per side to complete.
If the block includes a local anesthetic like lidocaine or bupivacaine, pain relief is usually rapid, often within minutes. This immediate relief helps confirm the diagnosis if the nerve is the source of the pain. The duration of numbness varies, typically lasting several hours for procedural blocks or a few days for diagnostic blocks.
When a corticosteroid is also injected, the full therapeutic effect of reducing inflammation may take several days or up to a week to become noticeable. While the anesthetic wears off quickly, the anti-inflammatory effect of the steroid can provide pain relief that lasts for weeks or even months. Patients may experience temporary numbness or tingling in the legs or feet if the nearby sciatic nerve is affected by the medication.