49
Complications of Pudendal Nerve Procedures

María Luz Padilla del Rey MD, FIPP, CIPS, EDPM¹, Alan Berkman BSc (Hons), MBChB, FFA 1 (SA), FRCPC, FIPP, CIPS², and Agnes R. Stogicza MD, FIPP, CIPS, ASRA-PMUC³

¹ University Hospital Complex of Cartagena, Region of Murcia, Spain
² Changepain Clinic, University of British Columbia, Vancouver BC, Canada
³ Saint Magdolna Private Hospital, Budapest, Hungary

Introduction

Chronic pelvic pain is defined as chronic or persistent pain perceived in structures related to the pelvis. It affects 7–24 % of the population [1] and is often associated with negative cognitive, behavioral, sexual, and emotional consequences as well as symptoms suggestive of lower urinary tract, sexual, bowel, pelvic floor or gynecologic dysfunction [2]. Pathologies of the pudendal nerve (PN) can be responsible for such pain.

The PN provides both motor and sensory fibers to the genital area from the anal and perirectal area up to the clitoris or penis. There are numerous possible causes for pudendal neuropathy, such as inflammatory or autoimmune illness, iatrogenic nerve damages and PN entrapments.

PN injections have utility in diagnosing and treating a wide variety of chronic pelvic pain syndromes.

This chapter discusses PN procedures, possible complications and ways to avoid them.

Anatomy

Origin

The PN is formed from the sacral plexus, arising from the ventral rami of the second, third and fourth spinal nerve roots; sometimes the first sacral nerve contributes fibers to the PN, and even more rarely the fifth. The PN is a thin (0.6–6.8 mm) [1] mixed nerve (sensory 50%, motor 20%, and autonomic 30%) that gives rise to three branches on each side of the body: rectal, perineal, and penile or clitoral branches [2] (Figure 49.1).

As with many other nerves, it is important to note there is considerable variation in the anatomy of the PN (size, specific pathways, structures innervated) and its inconsistent branches.

Path

This nerve has a very tortuous course through the pelvis and perineum. After the nerve roots leave the sacral foramen, they join together on the ventral surface of the piriformis muscle to form the PN, which travels into the gluteal region with the internal pudendal artery by passing through the greater sciatic foramen. The sacrospinous ligament (SSL) consists of dense connective tissue that attaches to the ischial spine laterally and to the lower part of the sacrum and coccyx medially. The sacrotuberous ligament (STL) has a broad fan-like origin from the posterosuperior and posteroinferior iliac spines and the entire lateral margin of the posterior sacrum; its fibers converge to the medial ischial tuberosity and additional fibers (known as the falciform process) extend to the ischial ramus. The SSL, along with the STL, divides the sciatic notches of the ischium and ilium into the lesser and greater sciatic foramen, respectively [3].

At the level of the ischial spine, the pudendal neurovascular bundle passes through a fascial plane between the gluteus maximus fascia and the SSL and the superior gemellus fascia. The PN and vessels then go through the ischioanal fossa into the pudendal canal (Alcock’s canal), which is formed by a splitting of the fascia covering the medial surface of the obturator internus muscle, and just before entering it or within it, the PN gives rise to the inferior rectal nerve. Within the Alcock´s canal, the PN divides into the perineal nerve and the dorsal nerve of the penis or clitoris. Common sites of compression or entrapment are the ischial spine, the pudendal or Alcock’s canal, the inner margin of the falciform process, which is part of the sacrotuberous ligament and the osteofibrotic canal at the base of the penis [4]).

Innervation

The inferior rectal nerve, originating near the proximal end of the Alcock’s canal, traverses the fatty tissue of the ischioanal fossa and supplies the levator ani muscle, the external anal sphincter, the mucous membrane of the lower half of the anal canal, the posterior vulva and the perianal skin. The inferior rectal nerve is, in part, responsible for conscious awareness of the need to defecate.
The perineal nerve gives off a deep motor portion to the muscles of the urogenital triangle (deep and superficial transverse perineal, external urethral sphincter, bulbospongiosus and ischiocavernosus muscles) and a superficial sensory branch that innervates the skin of the posterior part of the scrotum/labia majora (posterior scrotal/labial nerves) and the mucous membrane of the urethra and vagina. This nerve is involved in conscious awareness of the need to urinate.
The dorsal nerve of the clitoris/penis runs anteriorly along the inferior pubic ramus together with the pudendal artery deep to the perineal membrane which it pierces just below the pubic symphysis and extends along the dorsum of the clitoris/penis, supplying the overlying skin, the erectile tissue of the corpus cavernosum and crus of the penis/clitoris and the muscles involved in erection. Its autonomic component (parasympathetic) regulates both erectile and ejaculatory function (Table 49.1).

Table 49.1 Pudendal nerve innervation.

Pudendal nerve (PN) roots	Branchings	Autonomic innervation (30%)	Sensory innervation (50%)	Motor innervation (20%)
S1, S2–S4, S5 (sacral contributions may vary)	Inferior rectal nerve	Conscious awareness of the need to defecate	Perianal skin, lower half of the anal canal and posterior vulva	Levator ani muscle and external anal sphincter
	Perineal nerve	Conscious sensation of the need to urinate	Skin of the posterior part of the scrotum/labia majora and the mucous membrane of the urethra and vagina	Deep and superficial transverse perineal, external urethral sphincter, bulbospongiosus and ischiocavernosus muscles
	Dorsal nerve of the clitoris / penis	Erectile and ejaculatory function	Erectile tissue of the corpus cavernosum and crus of the penis / clitoris and the skin over its dorsum	Muscles involved in erection

Pudendal nerve (PN) roots

Branchings

Autonomic innervation (30%)

Sensory innervation (50%)

Motor innervation (20%)

S1, S2–S4, S5

(sacral contributions may vary)

Inferior rectal nerve

Conscious awareness of the need to defecate

Perianal skin, lower half of the anal canal and posterior vulva

Levator ani muscle and external anal sphincter

Perineal nerve

Conscious sensation of the need to urinate

Skin of the posterior part of the scrotum/labia majora and the mucous membrane of the urethra and vagina

Deep and superficial transverse perineal, external urethral sphincter, bulbospongiosus and ischiocavernosus muscles

Dorsal nerve of the clitoris / penis

Erectile and ejaculatory function

Erectile tissue of the corpus cavernosum and crus of the penis / clitoris and the skin over its dorsum

Muscles involved in erection

However, nerve terminations are complex and several anatomic possibilities have been previously described [5, 6].

Indications

Pudendal neuralgia, with PN entrapment being the most common etiology. Nevertheless, other causes have also been described: post-herpetic neuropathy, stretch neuropathy, peripheral polyneuropathy, postradiotherapy neuropathy, neoplastic compression, etc [7].
Chronic pelvic pain conditions in which this block could be beneficial (for example: bladder pain syndrome) [8].
Perineal anesthesia during obstetric procedures (vaginal birth during the second stage of labor, outlet forceps delivery, episiotomy, vaginal repairs).
Anesthesia involving the perineum after gynecologic, urologic (trans-rectal US-guided prostate biopsy, transurethral prostatectomy), and gastroenterologic surgeries (hemorrhoidectomies) [6, 9].
Diagnostic injections. PN block injection forms one of the five diagnostic criterion according to Nantes criteria [7].

Indications for Nerve Ablation and PRF

Pudendal neuralgia
Chronic pelvic pain.

Contraindications

Local (at target site) or systemic infection
Patient refusal or inability to cooperate
Allergy to local anesthetics
Malignancy at the needle entry site
Coagulopathy.

Technique

The best site for non-guided and guided infiltration, PRF treatment or cryoablation is the level of the ischial spine where the PN has not yet branched. The close topographic relationship to its tip as well as to the internal pudendal artery allows use of both structures as landmarks for any infiltration technique [1].

Needle: 21G–25G.

Drugs: 1–10 ml of local anesthetic ± steroid.