The pudendal nerve (S2-S4) is a mixed nerve mainly in charge of the sensory and motor supply of the perineum and external genitalia in both sexes. The nerve arises in the pelvic cavity from the sacral plexus, more specifically from the anterior rami of spinal nerves S2, S3 and S4. It leaves the pelvic cavity through the greater sciatic foramen, hooks around the ischial spine enters the perineum through the lesser sciatic foramen.
The main function of the pudendal nerve is to provide sensory supply to the external genitalia in both sexes and the skin around the anus, anal canal and perineum. It also provides motor supply for various pelvic muscles, the external urethral sphincter and the external anal sphincter.
This article will discuss the anatomy and function of the pudendal nerve.
|Origin||Sacral plexus (S2-S4)|
|Branches||Inferior anal (rectal) nerve
Dorsal nerve of the penis/clitoris
|Supply||Skin, organs, and muscles of the perineum and external genitalia in both sexes|
- Origin and course
- Branches and innervation
- Clinical relations
Origin and course
The pudendal nerve is one of the two main branches that originate from the sacral plexus, along with the sciatic nerve. It arises in the pelvis close to the upper border of the sacrotuberous ligament and ischiococcygeus muscle. The nerve courses inferiorly and leaves the pelvis through the greater sciatic foramen. After passing through the foramen, the nerve courses through the gluteal region, running dorsal to the sacrospinous ligament and medial to the internal pudendal vessels.
Accompanied by the internal pudendal artery and vein, and the nerve to the obturator internus, the pudendal nerve passes through the lesser sciatic foramen and into the pudendal canal (Alcock canal). The pudendal artery, vein and nerve are collectively referred to as the pudendal neurovascular bundle.
Upon entering the canal, the pudendal nerve gives rise to the inferior anal nerve (also called the inferior rectal nerve) that provides innervation for the external anal sphincter and the perianal skin. When it reaches the distal portion of the canal, the nerve bifurcates and gives rise to two more branches: the perineal nerve and the dorsal nerve of the penis/clitoris.
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Branches and innervation
The pudendal nerve gives off three branches:
- Inferior anal nerve
- Perineal nerve
- Dorsal nerve of the penis/clitoris
Inferior anal nerve
The inferior anal nerve (also known as the inferior rectal nerve or inferior hemorrhoidal nerve) is usually the first of three branches of the pudendal nerve. While in some individuals it can arise directly from the sacral plexus, it typically branches from the pudendal nerve in the Alcock's canal.
Upon arising, it exits the canal and traverses through the fat of the ischioanal fossa to reach the lateral aspect of the anal canal. The inferior anal nerve is a mixed nerve that provides sensory supply to the inferior portion of the anal canal (to the pectinate line) and the circumanal skin, and motor supply to the external anal sphincter. In addition, the inferior anal nerve may provide sensory innervation to the lower part of the vagina in females.
The perineal nerve is the second and the largest of the three branches of the pudendal nerve. It typically arises in the last portion of the Alcock's canal, or just as the pudendal nerve exits the canal. The perineal nerve bifurcates into deep (muscular) and superficial (cutaneous) perineal nerves.
- The deep branch supplies the muscles of the urogenital triangle (bulbospongiosus, ischiocavernosus and superficial transverse perineal muscle), the external urethral sphincter and the anterior parts of the external anal sphincter and levator ani.
- The superficial branch provides sensory supply to the posterior scrotal area in males, and the labia minora, vaginal vestibule, lower one-fifth of the vaginal canal and the posterior aspect of the labia majora and in females.
Dorsal nerve of the penis/clitoris
The dorsal nerve of the penis/clitoris is considered to be the terminal branch of the pudendal nerve. The dorsal nerve of the penis/clitoris is the sole sensory supplier of the external genitalia, thus it is crucial in maintaining normal sexual function. More specifically, in males, this nerve innervates the skin over the shaft of the penis, the prepuce, and the glans of the penis. In females, the dorsal nerve of the clitoris innervates the clitoral body and the glans.
To summarize, the pudendal nerve supplies the skin, organs, and muscles of the perineum; therefore, it is in charge of micturition, defecation, erection, ejaculation, and, in the female, parturition.
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Pudendal nerve entrapment syndrome
The pudendal nerve entrapment syndrome (PNE) is a severe and chronic condition. It is a result of mechanical or non-mechanical injury to the nerve that leads to neuropathic pain and neural dysfunction in the distribution of the pudendal nerve (pudendal neuralgia).
There are four types of PNE based on their anatomy. The nerve entrapment can occur around the greater sciatic notch (type I), between the sacrospinous and sacrotuberous ligaments (type II), in the Alcock canal (type III), or the entrapment of its terminal branches (type IV). It is usually caused by mechanical injuries during surgery, physical activity, accidents, direct compression, etc. There are also non-mechanical causes, which usually include systemic diseases that cause inflammation and swelling.
This syndrome is presented usually with severe and disabling pain located in the area of innervation of the pudendal nerve and its branches. Except for the pain, which is the most prominent symptom, it can cause numbness, sexual dysfunction and sphincter dysfunction. The treatment depends on the level of compression and damage. Milder compressions can be treated conservatively, whilst more severe injuries are usually treated surgically.
Pudendal nerve block
The pudendal nerve block is a procedure in which the local anesthetic is injected into the pudendal nerve causing the blockage of its neural transmission. This procedure was a popular technique in the last century, usually performed in order to provide perineal anesthesia during obstetric procedures. Now, this technique is rarely used since there are more modern techniques such as spinal or epidural anesthesia. But since this type of anesthesia is not always possible, the pudendal nerve block remains a suitable alternative.
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