Pudendal nerve

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"Pudendal" redirects here. For the artery or vein, see Superficial external pudendal (disambiguation).
Not to be confused with Inferior pudendal branch of the Posterior femoral cutaneous nerve.

Pudendal nerve
Inferior rectal nerves
perineal nerve
dorsal nerve of the penis
dorsal nerve of the clitoris
Identifiers
Latinnervus pudendus
MeSHD060525
TA98A14.2.07.037
TA26554
FMA19037
Anatomical terms of neuroanatomy]

The pudendal nerve is the main

external genitalia of both sexes and the skin around the anus and perineum, as well as the motor supply to various pelvic muscles, including the male or female external urethral sphincter and the external anal sphincter
.

If damaged, most commonly by childbirth, loss of sensation or fecal incontinence may result. The nerve may be temporarily anesthetized, called pudendal anesthesia or pudendal block.

The pudendal canal that carries the pudendal nerve is also known by the eponymous term "Alcock's canal", after Benjamin Alcock, an Irish anatomist who documented the canal in 1836.

Structure

Origin

Image showing the greater sciatic foramen (large foramen), and the lesser sciatic foramen, separated by the sacrospinous ligament. The pudendal nerve exits the pelvis through the greater sciatic foramen, passes over the ligament, and then reenters the pelvis through the lesser sciatic foramen.

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 the

sacral spinal nerves, with the primary contribution coming from the 4th.[2][4]: 215 [5]
: 157 

Course and relations

The pudendal nerve passes between the

ischiorectal fossa, being contained in a sheath of the obturator fascia termed the pudendal canal, along with the internal pudendal blood vessels.[6]
: 8 

Branches

Inside the pudendal canal, the nerve divides into branches, first giving off the

inferior rectal nerve, then the perineal nerve, before continuing as the dorsal nerve of the penis (in males) or the dorsal nerve of the clitoris (in females).[6]
: 34 

Nucleus

The nerve is a major branch of the sacral plexus,[7]: 950  with fibers originating in Onuf's nucleus in the sacral region of the spinal cord.[3]

Variation

The pudendal nerve may vary in its origins. For example, the pudendal nerve may actually originate in the

sacral nerve contribute fibers to the pudendal nerve, and even more rarely S5.[3]

Function

The pudendal nerve has both motor (control of muscles) and sensory functions. It also carries sympathetic autonomic fibers (but not parasympathetic fibers).[9][10]: 1738 

Sensory

The pudendal nerve supplies sensation to the

penile erection and clitoral erection.[13]
: 147 

Motor

Branches

puborectalis and either pubovaginalis in females or puboprostaticus in males)[11]: 422 [14] the external anal sphincter (via the inferior anal branch),[6]: 7  and male or female 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 via acetylcholine release. This means that during periods of increased acetylcholine release the skeletal 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 the somatic nervous system.)

It is also responsible for ejaculation.[16]

Clinical significance

Anesthesia

Approximate area of "saddle anesthesia" seen from behind (yellow highlight)

A pudendal nerve block, also known as a saddle nerve block, is a local anesthesia technique used in an obstetric procedure to anesthetize the perineum during labor.[17] In this procedure, an anesthetic agent such as lidocaine is injected through the inner wall of the vagina about the pudendal nerve.[18] Abnormal loss of sensation in the same region as a medical symptom is also sometimes termed saddle anesthesia.

Damage

The pudendal nerve can be compressed or stretched, resulting in temporary or permanent

fibrous tissue with subsequent loss of function.[19] Pudendal nerve entrapment, also known as Alcock canal syndrome, is very rare and is associated with professional cycling.[20] Systemic diseases such as diabetes and multiple sclerosis can damage the pudendal nerve via demyelination or other mechanisms.[6]: 37  A pelvic tumor (most notably a large sacrococcygeal teratoma), or surgery to remove the tumor, can also cause permanent damage.[21]

Unilateral pudendal nerve neuropathy inconsistently causes fecal 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.[19] This allows partial re-innervation from the opposite side after nerve injury.[19]

Imaging

The pudendal nerve is difficult to visualize on routine

CT, is used as the level of injection. A spinal needle is advanced via the gluteal 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 with cortisone and local anesthetic to confirm and also treat chronic pain of the external genitalia (known as vulvodynia in females), pelvic and anorectal pain.[22][23]

Nerve latency testing

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.[24]: 46  2 stimulating electrodes and 2 measuring electrodes are mounted on the examiner's gloved finger ("St Mark's electrode").[24]: 46 

History

The term pudendal comes from Latin pudenda, meaning external genitals, derived from pudendum, meaning "parts to be ashamed of".[25] The pudendal canal is also known by the eponymous term "Alcock's canal", after Benjamin Alcock, an Irish anatomist who documented the canal in 1836. Alcock documented the existence of the canal and pudendal nerve in a contribution about iliac arteries in Robert Bentley Todd's "The Cyclopaedia of Anatomy and Physiology".[26]

Additional images

  • The male pelvis, showing the pudendal nerve (centre right)
    The male pelvis, showing the pudendal nerve (centre right)
  • Schematic showing the structures innervated by the pudendal nerve
    Schematic showing the structures innervated by the pudendal nerve
  • Diagram of the course of the pudendal nerve in the male pelvis
    Diagram of the course of the pudendal nerve in the male pelvis

See also

This article uses anatomical terminology.
  • Neurogenic bladder

References

  1. ISBN 978-1-60831-756-1
    .
  2. ^
    ISBN 978-0-443-06676-4. {{cite book}}: |last= has generic name (help
    )
  3. ^
    S2CID 26706414
    .
  4. ISBN 978-0-7817-6274-8.{{cite book}}: CS1 maint: multiple names: authors list (link
    )
  5. ISBN 978-3-13-143071-7
    .
  6. ^
    ISBN 978-0-387-24846-2
    .
  7. ISBN 978-1-284-02542-2
    .
  8. PMID 17140150
    .
  9. ^
    PMID 31334992. {{cite journal}}: Cite journal requires |journal= (help
    )
  10. ISBN 978-0-12-515400-0. {{cite book}}: |first= has generic name (help)CS1 maint: multiple names: authors list (link
    )
  11. ^
    ISBN 978-0-8089-2306-0
    .
  12. ^
    ISBN 978-1-4160-3165-9.{{cite book}}: CS1 maint: multiple names: authors list (link
    )|page=Neurovascular Bundles of the Perineum
  13. ISBN 978-0-7817-4221-4.{{cite book}}: CS1 maint: multiple names: authors list (link
    )
  14. S2CID 20663667
    .
  15. PMID 18490916
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  16. ^ Penson, David F. (2002). Male Sexual Function: A Guide to Clinical Management. Annals of Internal Medicine.
  17. Cengage Learning
    . p. 727.
  18. ^ Satpathy, Hemant K.; et al. Isaacs, Christine; et al. (eds.). "Transvaginal Pudendal Nerve Block". WebMD LLC. Retrieved 19 July 2015.
  19. ^
    ISBN 978-3-030-66049-9
    .
  20. S2CID 20149549
    .
  21. S2CID 30584236
    .
  22. S2CID 1622253.{{cite journal}}: CS1 maint: multiple names: authors list (link
    )
  23. PMID 12876048.{{cite journal}}: CS1 maint: multiple names: authors list (link
    )
  24. ^
    ISBN 978-88-470-1542-5. {{cite book}}: |last= has generic name (help)CS1 maint: multiple names: authors list (link
    )
  25. ^ Harper, Douglas. "Pudendum". Online Etymology Dictionary. Retrieved 28 February 2014.
  26. S2CID 33298520
    .

External links

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