Pudendal Nerve block

The pudendal nerve is a sensory and motor nerve arising from the sacral plexus and forms from spinal nerve roots S2-S4. The pudendal nerve passes through the greater sciatic foramen, where it transverses through the sacrospinous and sacrotuberous ligaments. It then reenters the perineum through the lesser sciatic foramen and accompanies the internal pudendal artery and vein. The pudendal nerve courses through the ischiorectal fossa and then through Alcock’s canal, also known as the pudendal canal. Inside the pudendal canal, the nerve initially divides into the inferior rectal nerve and then gives off the perineal nerve. Ultimately, the nerve continues as the dorsal nerve innervating the penis and clitoris. The inferior rectal nerve innervates the external anal sphincter and the perianal skin. The perineal nerve innervates the bulbospongiosus, ischiocavernosus, and levator ani muscles and sends sensory branches to the skin of the labia majora and scrotum. The dorsal nerve branch is a sensory nerve ending supplying the skin of the clitoris and penis.

A pudendal nerve block is typically used to diagnose and treat pudendal nerve entrapment or pain associated with pudendal neuralgia. Patients describe the pain as a burning sensation and hyperalgesia in the external genital and perineal region. The injection can also be used for the management of painful conditions affecting the vulva, vagina and anus- these include vulvodynia, vestibulodynia, penile pain, proctalgia fugax and scrotal pain.

The procedure is usually done on an outpatient basis. Ultrasound can reliably be used for infiltration of the Pudendal nerves. This will improve the safety as well as the diagnostic utility of the procedure. A pudendal nerve block aims to block the nerve as it enters the lesser sciatic foramen, just medial to the attachment of the sacrospinous ligament to the ischial spine. The pudendal nerve is blocked at the entrance of the pudendal (Alcock’s) canal. The transducer is moved parallel and caudal to the lesser sciatic notch, and the pudendal nerve, artery, and vein are visualized inside the proximal part of the Alcock’s canal at the sharp angle between the coccygeus and internal obturator muscles.

Local anaesthetic and steroid can be injected under real-time ultrasound guidance targeting the Pudendal nerve at the Alcock’s canal. A positive response confirms the diagnosis of pudendal neuralgia and can also provide therapeutic benefit lasting weeks to months.

Pulsed radiofrequency treatment can be applied to the Pudendal nerves in patients who get a positive response to the local anaesthetic blocks. Pulsed radiofrequency can provide sustained pain relief in patients with pudendal neuralgia and pudendal nerve entrapment.

Injections are generally avoided in patients with systemic infection or skin infection over puncture site, bleeding disorders or coagulopathy, allergy to local anaesthetics or any of the medications to be administered.

Complications are rare, particularly if injections are performed under ultrasound guidance. Severe allergic reactions to local anaesthetics are uncommon. Post-procedural pain flare-up can occur in some patients especially if steroids are used in the injection. As the pudendal nerve lies close to the sciatic nerve, the injection of local anaesthetic can result in the heaviness of the leg(s), if the local anaesthetic tracks the sciatic nerve. This heaviness is temporary and would improve within a few hours.