| Pudendal nerve | |
|---|---|
 Pudendal nerve, course and branches in a male. | |
 Cross-section of female pelvis in which nerve emerges from S2, S3, and S4 extends between the uterus and the anus and into labium minus, labium majus and the clitoris | |
| Details | |
| From | Sacral nerves S2, S3, S4 |
| To | Inferior rectal nerves perineal nerve dorsal nerve of the penis dorsal nerve of the clitoris |
| Identifiers | |
| Latin | nervus pudendus |
| MeSH | D060525 |
| TA98 | A14.2.07.037 |
| TA2 | 6554 |
| FMA | 19037 |
| Anatomical terms of neuroanatomy | |
Thepudendal nerve is the mainnerve of theperineum.[1]: 274 It is amixed (motor and sensory) nerve and also conveyssympatheticautonomic fibers. It carries sensation from theexternal genitalia of both sexes and the skin around theanus and perineum, as well as themotor supply to various pelvic muscles, including themale orfemale external urethral sphincter and theexternal anal sphincter.
If damaged, most commonly by childbirth, loss of sensation orfecal incontinence may result. The nerve may be temporarily anesthetized, calledpudendal anesthesia or pudendal block.
Thepudendal canal that carries the pudendal nerve is also known by the eponymous term "Alcock's canal", afterBenjamin Alcock, an Irish anatomist who documented the canal in 1836.
The pudendal nerve is paired, meaning there are two nerves, one on the left and one on the right side of the body. Each is formed as three roots immediately converge above the upper border of thesacrotuberous ligament and thecoccygeus muscle.[2] The three roots become two cords when the middle and lower root join to form the lower cord, and these in turn unite to form the pudendal nerve proper just proximal to thesacrospinous ligament.[3] The three roots are derived from theventral rami of the 2nd, 3rd, and 4thsacral spinal nerves, with the primary contribution coming from the 4th.[2][4]: 215 [5]: 157
The pudendal nerve passes between thepiriformis muscle andcoccygeus (ischiococcygeus) muscles and leaves the pelvis through the lower part of thegreater sciatic foramen.[2] It crosses over the lateral part of thesacrospinous ligament and reenters the pelvis through thelesser sciatic foramen. After reentering the pelvis, it accompanies theinternal pudendal artery andinternal pudendal vein upwards and forwards along the lateral wall of theischiorectal fossa, being contained in a sheath of theobturator fascia termed thepudendal canal, along with the internal pudendal blood vessels.[6]: 8
Inside the pudendal canal, the nerve divides into branches, first giving off theinferior rectal nerve, then theperineal nerve, before continuing as thedorsal nerve of the penis (in males) or thedorsal nerve of the clitoris (in females).[6]: 34
The nerve is a major branch of thesacral plexus,[7]: 950 with fibers originating inOnuf's nucleus in thesacral region of thespinal cord.[3]
The pudendal nerve may vary in its origins. For example, the pudendal nerve may actually originate in thesciatic nerve.[8] Consequently, damage to the sciatic nerve can affect the pudendal nerve as well. Sometimesdorsal rami of the firstsacral nerve contribute fibers to the pudendal nerve, and even more rarelyS5.[3]
The pudendal nerve has both motor (control of muscles) and sensory functions. It also carriessympathetic autonomic fibers (but notparasympathetic fibers).[9][10]: 1738
The pudendal nerve supplies sensation to thepenis in males, and to theclitoris in females, which travels through the branches of both thedorsal nerve of the penis and thedorsal nerve of the clitoris.[11]: 422 The posteriorscrotum in males and thelabia majora in females are also supplied, via theposterior scrotal nerves (males) orposterior labial nerves (females). The pudendal nerve is one of several nerves supplying sensation to these areas.[12] Branches also supply sensation to theanal canal.[6]: 8 By providing sensation to the penis and the clitoris, the pudendal nerve is responsible for theafferent component ofpenile erection andclitoral erection.[13]: 147
Branchesinnervate muscles of theperineum and thepelvic floor; namely, thebulbospongiosus and theischiocavernosus muscles respectively[12], thelevator ani muscle (including theIliococcygeus,pubococcygeus,puborectalis and eitherpubovaginalis in females orpuboprostaticus in males)[11]: 422 [14] theexternal anal sphincter (via the inferior anal branch),[6]: 7 andmale orfemale external urethral sphincter.[11]: 424–425
As it functions to innervate the external urethral sphincter it is responsible for the tone of the sphincter mediated viaacetylcholine release. This means that during periods of increased acetylcholine release theskeletal muscle in the external urethral sphincter contracts, causing urinary retention. Whereas in periods of decreased acetylcholine release the skeletal muscle in the external urethral sphincter relaxes, allowing voiding of the bladder to occur.[15] (Unlike the internal sphincter muscle, the external sphincter is made of skeletal muscle, therefore it is under voluntary control of thesomatic nervous system.)
It is also responsible forejaculation.[16]
The pudendal nerve may be tested by elicitation of theanocutaneous reflex ("anal wink").[17]
Apudendal nerve block, also known as asaddle nerve block, is alocal anesthesia technique used in anobstetric procedure to anesthetize the perineum duringlabor.[18] In this procedure, an anesthetic agent such aslidocaine is injected through the inner wall of thevagina about the pudendal nerve.[19] Abnormal loss of sensation in the same region as a medical symptom is also sometimes termedsaddle anesthesia.
The pudendal nerve can be compressed or stretched, resulting in temporary or permanentneuropathy. Injury to the pudendal nerve manifests more as sensory problems (pain or alteration/loss of sensation) rather than loss of muscle control.[9] Irreversible nerve injury may occur when nerves are stretched by 12% or more of their normal length.[6]: 655 If the pelvic floor is over-stretched, acutely (e.g. prolonged or difficult childbirth) or chronically (e.g. chronic straining duringdefecation caused byconstipation), the pudendal nerve is vulnerable to stretch-induced neuropathy.[6]: 655 After repeated traction of the pudendal nerve, it starts to be replaced byfibrous tissue with subsequent loss of function.[20]Pudendal nerve entrapment, also known asAlcock canal syndrome, isneuropathic pain in the distribution of the pudendal nerve. It is caused by entrapment of the nerve. The condition is estimated to have a prevalence of 1 in 100000,[21] and is sometimes associated with professionalcycling.[22] Systemic diseases such asdiabetes andmultiple sclerosis can damage the pudendal nerve viademyelination or other mechanisms.[6]: 37 A pelvic tumor (most notably a largesacrococcygeal teratoma), or surgery to remove the tumor, can also cause permanent damage.[23]
Unilateral pudendal nerve neuropathy inconsistently causesfecal incontinence in some, but not others. This is because crossover innervation of the external anal sphincter occurs in some individuals.[6]: 34 There is significant overlap of the innervation of the external anal sphincter from the pudendal nerves of both sides.[20] This allows partial re-innervation from the opposite side after nerve injury.[20]
The pudendal nerve is difficult to visualize on routineCT orMR imaging, however under CT guidance, a needle may be placed adjacent to the pudendalneurovascular bundle. Theischial spine, an easily identifiable structure onCT, is used as the level of injection. A spinal needle is advanced via thegluteal muscles and advanced within several millimeters of the ischial spine. Contrast (X-ray dye) is then injected, highlighting the nerve in the canal and allowing for confirmation of correct needle placement. The nerve may then be injected withcortisone and local anesthetic to confirm and also treat chronic pain of the external genitalia (known asvulvodynia in females), pelvic and anorectal pain.[24][25]
The time taken for a muscle supplied by the pudendal nerve to contract in response to an electrical stimulus applied to the sensory and motor fibers can be quantified. Increased conduction time (terminal motor latency) signifies damage to the nerve.[26]: 46 2 stimulating electrodes and 2 measuring electrodes are mounted on the examiner's gloved finger ("St Mark's electrode").[26]: 46
The term pudendal comes fromLatinpudenda, meaning external genitals, derived frompudendum, meaning "parts to be ashamed of".[27] Thepudendal canal is also known by the eponymous term "Alcock's canal", afterBenjamin Alcock, an Irish anatomist who documented the canal in 1836. Alcock documented the existence of the canal and pudendal nerve in a contribution aboutiliac arteries inRobert Bentley Todd's "The Cyclopaedia of Anatomy and Physiology".[28]
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