Pudendal Nerve Diagram: Location, Branches, and Function

The pudendal nerve is a paired nerve that originates from the lower spinal cord, travels deep through the pelvis, and supplies sensation and muscle control to the genitals, perineum, and anal region. It arises from the ventral branches of spinal nerve roots S2 through S4, though the exact combination varies from person to person.¹ Understanding this nerve’s path and branching pattern matters because it controls functions most people take for granted: bowel and bladder continence, sexual arousal, and the ability to sit without pain.

Where the Pudendal Nerve Begins

The pudendal nerve forms from nerve fibers that exit the sacrum, the triangular bone at the base of your spine. In anatomy texts, you will almost always see it labeled as arising from S2, S3, and S4. That pattern does predominate, but a large combined analysis of over 500 specimens found the classic S2–S4 origin in only about 55% of cases, with other combinations making up the rest.² Some people have contributions from S1 or lack contribution from one of the typical roots. This is worth knowing because it means the nerve’s behavior during surgery, injury, or compression is not perfectly predictable from a textbook diagram alone.

Once these sacral roots merge, the resulting pudendal nerve trunk is a modest-sized structure. Cadaveric measurements show it is typically around 4.5 mm wide in the pelvis, though this can range from about 2.5 to over 6 mm. The nerve trunk itself forms a short distance from the ischial spine, a bony landmark that surgeons use to locate the nerve during procedures.³ In about 61.5% of specimens, there is a single trunk at this point; in the remaining cases, the nerve has already begun splitting before it reaches the ischial spine.

The Route Through the Pelvis

After forming, the pudendal nerve exits the pelvis through the greater sciatic foramen, hooks around the ischial spine and sacrospinous ligament, and then re-enters the pelvis through the lesser sciatic foramen. This looping path is unusual compared to most nerves and creates the first of several tight spots where the nerve can get pinched. From there, it enters a tunnel of connective tissue along the inner wall of the ischium known as Alcock’s canal (also called the pudendal canal). This canal is roughly 40.5 mm long on average, though it can be as short as 20.5 mm or as long as 54.5 mm.³

Alcock’s canal is a clinically important structure because nerve compression there is one of the most recognized causes of pudendal neuralgia. Surgical release of the nerve along this canal, from the ischial spine through to the exit point, has been described as a viable approach.⁴ After exiting the canal, the nerve fans out into its three terminal branches, each heading to a different part of the pelvic floor.

The Three Main Branches

Diagrams of the pudendal nerve almost always depict three terminal branches. Each one has a distinct job, and understanding the split helps explain why pudendal nerve problems can present so differently from one person to the next. Damage or compression affecting just one branch can cause isolated symptoms while leaving other functions intact.

Inferior Rectal Nerve

The inferior rectal nerve branches off early, sometimes even before the main trunk enters Alcock’s canal. In one dissection study, the inferior rectal nerve entered the pudendal canal in only about 42% of cases; in the remaining specimens it bypassed the canal entirely, passing behind the sacrospinous ligament and heading directly into the fat-filled ischioanal fossa.³ This variability is clinically relevant: a nerve block targeting the pudendal canal might miss the inferior rectal branch if it takes the alternative route.

This branch supplies motor control to the external anal sphincter, the muscle you consciously tighten to maintain bowel continence. It also carries sensory information from the skin around the anus. Older dissection work identified multiple nerve branches reaching the external anal sphincter, including one arising from the external perineal nerve and an independent posterior branch, all ultimately stemming from the pudendal plexus.⁵

Perineal Nerve

The perineal nerve is the largest of the three branches. It divides further into superficial and deep rami. The superficial branches carry sensation from the skin of the perineum, the posterior aspect of the scrotum or labia, and the vaginal vestibule. The deep branches are motor fibers. They innervate the bulbospongiosus muscle (which contributes to ejaculation in males and vaginal constriction in females), the ischiocavernosus muscle, and part of the external urethral sphincter.⁶ Through these connections, the perineal nerve has a hand in both urinary continence and sexual function.

Dorsal Nerve of the Penis or Clitoris

The third terminal branch is the dorsal nerve of the penis (in males) or the dorsal nerve of the clitoris (in females). This is primarily a sensory nerve, responsible for transmitting the fine touch and pressure signals that are central to sexual arousal and orgasm. In females, neuronal tracing studies have shown that sensory fibers from the clitoris merge into the dorsal clitoral nerve, which then joins the pudendal nerve trunk to relay signals up to the spinal cord and brain.⁷

The dorsal nerve follows the ischiopubic ramus along the crura (the internal “legs” of the erectile bodies) and arches dorsally to reach the shaft of the clitoris or penis. Along this trajectory, the nerve bundles change their arrangement. Near the crura, they sit in larger, tightly clustered groups between the bone and the erectile tissue. As the nerve progresses along the shaft, bundles fan out and become smaller and more spread apart. In the clitoris, bundles ultimately distribute between roughly the 10-o’clock and 2-o’clock positions around the dorsal surface of the body before innervating the glans and prepuce.⁸ In both sexes, the dorsal nerve travels through a bony groove on the underside of the pubic bone, sometimes called the sulcus nervi dorsalis.⁹ This groove is another potential site of compression, particularly in cyclists and others who put sustained pressure on the perineum.

What the Pudendal Nerve Controls

Broadly, the pudendal nerve serves three overlapping functions: continence, sexual response, and sensation in the perineal region. The external anal sphincter, the muscle that allows you to hold in stool voluntarily, is under pudendal nerve control via the inferior rectal branch. The external urethral sphincter, which helps you stop urinating mid-stream, receives input from the perineal branch. When the pudendal nerve is damaged, fecal incontinence, urinary incontinence, or both can result.¹⁰

In the continence system, the pudendal nerve is only one player. The internal anal sphincter, which operates involuntarily, is controlled by the autonomic nervous system and is responsible for passive continence at rest. The puborectalis sling of the pelvic floor creates the anorectal angle. Anal cushions and mucosal folds add further seal. But the external sphincter, controlled by the pudendal nerve from S2 through S4, is what gives you active, voluntary control during urgency.¹¹

For sexual function, the pudendal nerve’s circuitry is essential. Research supports the concept that pudendal afferents relay genital sensory information to higher brain centers involved in arousal, erection, penile rigidity, ejaculation, and micturition reflexes.¹² People with pudendal nerve injuries frequently report reduced genital sensation and difficulty reaching orgasm, alongside the more commonly discussed pain symptoms.

Pudendal Nerve Entrapment and Neuralgia

Pudendal neuralgia is chronic pain in the territory of the pudendal nerve. It can be excruciating and is often underdiagnosed because its symptoms overlap with many other pelvic conditions. The most widely used diagnostic framework is the Nantes criteria, which require five features to be present: pain in the anatomical territory of the pudendal nerve, pain that worsens with sitting, pain that does not wake you at night, no objective sensory loss on clinical exam, and a positive response to an anesthetic pudendal nerve block.¹³ The criteria also list exclusions, such as pain that is purely in the coccyx, buttocks, or lower abdomen, and pain that is exclusively paroxysmal or presents as itching alone.

The nerve can become entrapped at several points along its winding path. The classic sites are between the sacrospinous and sacrotuberous ligaments, within Alcock’s canal, and, as one cadaveric study demonstrated, at the transition point between Alcock’s canal and the base of the penis, where the nerve passes through a tight osteofibrotic tunnel formed by the pubic bone, the suspensory ligament, and the ischiocavernosus body.¹⁴ That study found pseudoneuromatous thickening in some specimens, suggesting chronic irritation, and noted that people exposed to repetitive mechanical pressure in this region are at particular risk. Cyclists, rowers, and anyone who sits for very long periods on hard surfaces are the populations most commonly mentioned.

How the Nerve Is Imaged and Tested

Because the pudendal nerve runs deep within the pelvis, it has historically been difficult to see on standard imaging. That has changed with high-resolution MRI, particularly magnetic resonance neurography at 3 Tesla field strength, which can show the nerve and its branches in enough detail to identify abnormalities. One study of patients with chronic pudendal neuralgia found nerve hyperintensity on diffusion-weighted MRI scans in 42 out of a group evaluated, with the abnormality being unilateral in most and bilateral in about a fifth of cases. In over half of those with nerve signal changes, pathologies likely causing neuropathy were also identified.¹⁵ High-resolution ultrasound is another noninvasive option that is gaining traction, and 3T MR neurography is considered a promising technique for evaluating both normal anatomy and pathological changes.¹⁶

Electrophysiological testing also exists, specifically pudendal nerve terminal motor latency (PNTML) testing, which measures how quickly a signal travels along the nerve. The test is operator-dependent, though. Research found that less experienced examiners tended to record longer latencies, resulting in false-positive rates above 20%, and that it took performing the test on roughly 40 to 50 patients before a trainee’s results matched those of an experienced instructor.¹⁷ This means that in centers with limited experience, PNTML results should be interpreted cautiously.

Diagnostic and Therapeutic Nerve Blocks

A pudendal nerve block serves two purposes: it helps confirm the diagnosis of pudendal neuralgia, and it can provide meaningful pain relief. The procedure involves injecting a local anesthetic, sometimes combined with a corticosteroid, near the nerve under imaging guidance. CT-guided blocks targeting the pudendal canal have shown significant drops in pain scores. In one series, mean pain scores fell from about 6.1 before the procedure to about 2.1 afterward. Of 31 patients in that study, 14 went on to surgical nerve release based on initial improvement from the blocks, and all 14 improved with surgery. Two patients had long-term relief from the blocks alone, and two had no response, effectively ruling out pudendal neuralgia as the diagnosis.¹⁸

Fluoroscopy-guided blocks have also been studied. A retrospective case series reported that about half of patients achieved at least 30% pain relief at two weeks, and patients also reported reductions in medication use and improvements in daily activities.¹⁹ A modified fluoroscopic technique targeting the neurovascular bundle just anterior and medial to the ischial spine has been proposed to improve accuracy and reduce false negatives.²⁰ The choice of imaging modality varies by institution, but the trend is toward more precise guidance to ensure the anesthetic actually reaches the nerve rather than the surrounding tissue.

Treatment When the Nerve Is Damaged or Entrapped

Management of pudendal neuralgia typically starts with conservative approaches: behavioral changes like using a cushion with a cutout to avoid perineal pressure while sitting, medications for neuropathic pain, and pelvic floor physical therapy.²¹ However, patient experience with physical therapy specifically for pudendal neuralgia has been underwhelming in at least one cross-sectional study. Among 144 respondents, the average self-reported improvement was in the range of “no change to minimal improvement,” with about two-thirds of participants reporting little to no benefit and 12% actually reporting worsening symptoms. Only about one in five reported much or very much improvement.²² This does not mean physical therapy is useless for all pelvic floor problems, but for nerve entrapment specifically, it may not address the underlying mechanical issue.

Surgical decompression is considered when conservative treatment and nerve blocks have failed. The only randomized controlled trial on the subject compared surgery to non-surgical management and found that 71% of the surgery group had improved pain at one year, compared to about 13% of the non-surgery group. Eight of the surgical patients maintained improvement at four years, and no complications were encountered.²³ A systematic review and meta-analysis pooling 19 studies and 810 patients estimated the overall rate of significant pain relief across all surgical techniques at about 67%. Laparoscopic approaches had the highest success rate, around 91%, while perineal approaches came in around 69% and transgluteal around 50%, though there was substantial variability across studies.²⁴ Patient age and follow-up duration both influenced outcomes, which partly explains the wide range.

Childbirth and the Pudendal Nerve

Vaginal delivery is one of the most common causes of pudendal nerve stretch injury. A prospective study measuring nerve conduction before and after childbirth found significant slowing of the pudendal nerve signal in both first-time and experienced mothers. Heavier babies and a longer active second stage of labor were both associated with greater nerve damage. The left side consistently showed more injury than the right.²⁵

A 3D computer simulation of the second stage of labor showed that the nerves innervating the anal sphincter get stretched beyond the 15% strain threshold known to cause permanent damage in other peripheral nerves. The degree of perineal descent during pushing directly influenced how much strain the nerve experienced.²⁶ This helps explain why some women develop fecal incontinence or reduced perineal sensation after delivery, particularly after long or difficult labors involving large babies. For most women, the nerve recovers over weeks to months, but repeated vaginal deliveries accumulate strain, and some damage can be permanent.

Why Anatomical Variation Matters for Procedures

If every pudendal nerve followed the same textbook path, nerve blocks, surgical decompressions, and perineal surgeries would be much more straightforward. In reality, the nerve varies in its root contributions, trunk formation, branching pattern, and relationship to Alcock’s canal. As mentioned earlier, the inferior rectal nerve skips the pudendal canal entirely in over half of dissected specimens.³ This means a block performed inside the canal could leave anal sensation and sphincter control unaffected, potentially leading a clinician to wrongly conclude that the pudendal nerve is not involved.

These variations also have implications for pelvic surgeries unrelated to the nerve itself. Procedures involving the sacrospinous ligament, such as vaginal vault suspension for pelvic organ prolapse, risk injuring the pudendal nerve where it hooks around that ligament. Knowing the range of distances between the nerve trunk and the ischial spine (roughly 14.5 to 37 mm) helps surgeons plan safe fixation points. In laparoscopic or robotic surgery for rectal cancer or endometriosis, awareness that the nerve’s trajectory and branching can differ between the two sides of the same patient reduces the chance of inadvertent damage. Preoperative MR neurography is increasingly used to map the nerve before surgery in cases where entrapment or anatomical ambiguity is suspected.¹⁶