Topics

Topic

design image
Pudendal nerve

The pudendal nerve is the major somatic nerve of the perineum, providing both sensory and motor innervation. It arises from the ventral rami of S2–S4 spinal nerves, part of the sacral plexus. The nerve exits the pelvis via the greater sciatic foramen, courses around the sacrospinous ligament and ischial spine, and re-enters through the lesser sciatic foramen to run within the pudendal (Alcock’s) canal along the lateral wall of the ischiorectal fossa.

Along its course, the pudendal nerve gives rise to three main terminal branches: the inferior rectal nerve, the perineal nerve, and the dorsal nerve of the penis or clitoris. Through these branches, it innervates the external anal sphincter, urethral sphincter, perineal muscles, and skin of the perineum, scrotum, penis, or vulva.

The pudendal nerve is clinically significant in pelvic floor dysfunction, incontinence, chronic pelvic pain, and pudendal nerve entrapment syndrome. It is also a landmark in regional anesthesia for obstetrics and gynecology.

Synonyms

  • Nervus pudendus

  • Pelvic floor nerve

  • Alcock’s canal nerve

Function

  • Motor: supplies external anal sphincter, urethral sphincter, and perineal muscles

  • Sensory: provides sensation to external genitalia, anal canal, perineum, and posterior scrotum/labia

  • Autonomic integration: contributes to continence and sexual reflexes through mixed somatic and autonomic pathways

MRI Appearance

T1-weighted images:

  • Pudendal nerve appears as a linear low-to-intermediate signal structure within Alcock’s canal

  • Surrounded by hyperintense fat for contrast

T2-weighted images:

  • Normal nerve: intermediate signal intensity with fascicular pattern

  • Entrapment or inflammation: may show increased T2 hyperintensity

STIR:

  • Suppresses fat and highlights perineural edema or inflammatory changes as bright hyperintense signal

  • Useful in detecting pudendal neuropathy or entrapment

PD (Proton Density):

  • Nerve fascicles appear as alternating low-to-intermediate signal strands

  • Helps delineate nerve from adjacent vessels and fascia

T1 Post-Gadolinium (standard 2D):

  • Normal nerve: does not enhance significantly

  • Pathological nerve (neuritis, tumor, entrapment): shows abnormal focal or diffuse enhancement

3D T2-weighted Imaging:

  • Provides isotropic, high-resolution images of the nerve along its entire course

  • Nerve fascicles appear as intermediate signal strands within hypointense perineural sheath

  • Excellent for mapping nerve course through greater sciatic foramen, ischial spine, and Alcock’s canal

  • Allows multiplanar reconstructions to identify nerve entrapment by ligaments or masses

3D T1 Post-Gadolinium Imaging:

  • Normal pudendal nerve remains non-enhancing, surrounded by enhanced soft tissues

  • Abnormal findings:

    • Entrapment neuropathy: focal enhancement along nerve course

    • Inflammation/tumor: diffuse or nodular enhancement

    • Post-surgical scarring: enhancing perineural tissue encasing non-enhancing nerve fascicles

  • Very useful for differentiating nerve vs. vessel vs. scar tissue

CT Appearance

Non-contrast CT:

  • Pudendal nerve is not directly visualized due to poor soft tissue contrast

  • Bony landmarks (ischial spine, sacrospinous ligament, obturator internus fascia) can suggest nerve location

CT Post-Contrast:

  • Nerve itself remains poorly visualized

  • Enhancement of surrounding tissues may indicate inflammation, mass effect, or entrapment causes

  • Used primarily for guidance in pudendal nerve blocks

MRI image

Pudendal nerve MRI axial anatomy image-0

MRI image

Pudendal nerve MRI axial anatomy image-img-00000-00000

MRI image

Pudendal nerve MRI axial anatomy image-img-00000-00000_00002

MRI image

Pudendal nerve MRI axial anatomy image-img-00000-00000_00003

MRI image

Pudendal nerve MRI axial anatomy image-img-00000-00000_00004

CT image

Pudendal nerve CT axial image 0

CT image

Pudendal nerve CT axial image 1

MRI images

Pudendal nerve