Pudendal nerve block

Intermediate to advanced. The nerve is deep and small, and the internal pudendal artery, the sciatic nerve and (with the perineal route) the rectum are close.

The pudendal nerve forms from the ventral rami of S2–S4. It leaves the pelvis through the greater sciatic foramen below piriformis, curves around the back of the ischial spine and sacrospinous ligament, and re-enters through the lesser sciatic foramen into the pudendal (Alcock's) canal on the side wall of the ischioanal fossa.

At the ischial spine the nerve lies in the interligamentous plane between the sacrotuberous ligament (behind) and the sacrospinous ligament (in front), usually just medial to the internal pudendal artery.

Its branches are the inferior rectal nerve (anal sphincter and skin around the anus), the perineal nerve (perineum, scrotum or labia, urethral sphincter) and the dorsal nerve of the penis or clitoris.

The sciatic nerve lies only a few centimetres lateral, so large volumes or lateral injection can weaken the leg.

• Ischial spine (felt through the vagina in the transvaginal approach).
• Ischial tuberosity.
• Posterior superior iliac spine and greater trochanter (transgluteal scanning position).
• Anus and perineal body (perineal approach).

• Anorectal surgery: haemorrhoidectomy, fistula, fissure.
• Perineal and vaginal surgery, and perineal repair.
• Second stage of labour and instrumental delivery (transvaginal approach by the obstetrician).
• Children's genital surgery, including hypospadias repair.
• Diagnosis and treatment of pudendal neuralgia (pain clinic).

• Pudendal nerve (S2–S4)
• Inferior rectal, perineal and dorsal penile or clitoral branches

Surface anatomy, relevant structures and landmarks

Transvaginal: the ischial spine is felt through the side wall of the vagina. Perineal: the needle enters between the anus and the ischial tuberosity.

Positioning

Lithotomy for the transvaginal and perineal approaches.

Block technique

• Transvaginal (obstetric): with a needle guide, place the tip just through the vaginal wall behind and below the ischial spine, aspirate and inject 10 mL each side.
• Perineal: insert the needle midway between the anus and the ischial tuberosity, aiming at the ischial spine guided by a finger in the rectum or vagina, to about 5–6 cm in adults.
• Aspirate carefully before each injection.

Needle choice

22 G, 100–150 mm with a guide for the transvaginal approach; 80–100 mm for the perineal and transgluteal approaches.

Neurostimulation technique

Optional: anal sphincter contraction at 0.5 mA confirms the needle is near the nerve.

Choice of local anaesthetic (including volume)

• Adults: 8–10 mL each side of 0.25–0.5% bupivacaine or levobupivacaine, or 0.375–0.5% ropivacaine.
• Children: 0.2–0.3 mL/kg each side of 0.2% ropivacaine or 0.25% levobupivacaine.
• Check the total dose for bilateral blocks: use the dose calculator.

Show scan

GMm Gluteus maximus muscleSTL Sacrotuberous ligamentPn Pudendal nerveSSL Sacrospinous ligamentIS Ischial spine

Show scan

IT Ischial tuberosityPNVB Pudendal neurovascular bundlesTP Superficial transverse perineal muscle

Positioning

Prone with a pillow under the pelvis. Operator on the side of the block.

Scanning technique

• Place a curvilinear probe across the buttock, between the PSIS and the greater trochanter, and find the curved bright line of the ilium.
• Slide down until the bone line becomes the short, straight ischial spine.
• Find the sacrotuberous ligament (a bright band running medially from superficial) and the sacrospinous ligament (deeper, attached to the spine).
• Use colour Doppler to find the internal pudendal artery just medial to the spine. The nerve is usually just medial to the artery.
• Insert the needle in plane from medial to lateral into the plane between the two ligaments, next to the artery, and inject. Coming from the medial side keeps the needle path away from the sciatic nerve, which lies lateral to the spine.
• Below the spine: slide the probe a little caudally. Obturator internus curves over the edge of the ischium and drops away into the pelvis (the 'waterfall'). The nerve and artery lie on its surface under the sacrotuberous ligament, entering the pudendal canal. This is an alternative target, again with the needle from medial to lateral.
• Perineal (ischiorectal fossa) approach: in lithotomy, place a linear probe between the anus and the ischial tuberosity. Find the tuberosity and its shadow laterally, and the superficial transverse perineal muscle medially. The pudendal neurovascular bundle lies in the pudendal (Alcock's) canal on the inner side of the tuberosity, under the obturator internus fascia; colour Doppler shows the artery. Insert the needle in plane from medial to lateral and inject beside the bundle.

Structures to identify

• Gluteus maximus
• Sacrotuberous ligament
• Ischial spine
• Sacrospinous ligament
• Internal pudendal artery
• Pudendal nerve
• Obturator internus (below the spine)
• Perineal approach: ischial tuberosity, superficial transverse perineal muscle and the pudendal neurovascular bundle

Position / ergonomics

Stand on the side of the block, screen on the opposite side.

Probe

Curvilinear in adults; linear in children and for the perineal approach in the ischiorectal fossa.

Settings

Abdominal or deep preset, depth 8–10 cm, colour Doppler on.

Depth

4–8 cm in adults.

Needle size

22 G, 80–100 mm.

Needling technique

In plane from medial to lateral. This keeps the sciatic nerve, which lies lateral, out of the needle path.

Optimal needle-tip position

In the interligamentous plane, medial to the ischial spine and next to (not in) the internal pudendal artery.

Drug choice

See above.

Volume

8–10 mL each side in adults.

Optimal current if nerve stimulation is used

0.5 mA.

Muscle responses acceptable

Contraction of the anal sphincter. Foot or hamstring movement means the sciatic nerve: pull back and redirect medially.

Testing block success

• Numb skin around the anus and perineum (awake patients)
• Relaxed anal sphincter

Not usually used. Catheters have been described for chronic pain.

• Find the artery first with colour Doppler: the nerve is usually just medial to it.
• Keep the volume to about 10 mL each side to limit spread to the sciatic nerve.
• For midline anal surgery, block both sides.
• Tell the patient their leg may feel weak for a few hours.

• Di Giuseppe and colleagues (2020) randomised 49 patients having open haemorrhoidectomy under spinal anaesthesia: adding an ultrasound-guided pudendal block lowered pain at 6 and 24 hours and shortened hospital stay.
• Pan and colleagues (2025) randomised 78 patients having stapled haemorrhoid surgery: ultrasound-guided pudendal block gave lower pain scores in the first 18 hours and better recovery than local infiltration.
• Ozen and Ozen (2023) found ultrasound-guided pudendal and dorsal penile blocks equally effective in children having distal hypospadias repair.
• Vita and colleagues (2026) reviewed ultrasound-guided pudendal injection for pudendal neuralgia.

• Di Giuseppe M, Saporito A, La Regina D, et al. Ultrasound-guided pudendal nerve block in patients undergoing open hemorrhoidectomy: a double-blind randomized controlled trial. Int J Colorectal Dis 2020;35:1741–1747. PubMed
• Pan P, Jiang J, Zhang X, Yang W, Ding W. Ultrasound-guided pudendal nerve block for postoperative pain management in procedures for prolapse and hemorrhoids: a randomized, double-blinded trial. Int J Colorectal Dis 2025;40:159. PubMed
• Ozen V, Ozen N. Ultrasound-guided pudendal nerve block versus ultrasound-guided dorsal penile nerve block for pediatric distal hypospadias surgery. Urol Int 2023;107:370–376. PubMed
• Vita F, Donati D, Vender F, et al. Ultrasound-guided infiltration of the pudendal nerve: a technical approach for neuropathic pain management. J Ultrasound 2026;29:199–204. PubMed