Pudendal nerve entrapment (PNE) syndrome is a rare and under-diagnosed condition associated with chronic pain, sexual dysfunction and impaired sphincter control due to pudendal nerve compression.
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Clinical presentation
PNE commonly manifests as neuropathic pain in the genitals, perineum or anus. The pain is typically worse when seated for long periods and may be associated with a sensation of swelling in the affected region.
PNE can also cause sexual dysfunction, including dyspareunia, persistent sexual arousal, erectile dysfunction or premature ejaculation 2. Other manifestations include sphincter dysfunction, such as urinary frequency or hesitancy, fecal incontinence and dyschezia.
Etiology
The pudendal nerve arises from the S2-S4 roots of the sacral plexus, carrying both sensory and motor fibers. In the setting of an entrapment syndrome, the nerve is compressed from injury, repetition, or adjacent structures. Causes include:
childbirth with vaginal delivery
chronic constipation
pelvic surgery
repetitive minor trauma over several months or years, such as cycling or horse riding
Four types of PNE syndromes have been identified based on the site of entrapment 1:
type I – as the nerve exits the greater sciatic foramen
type II – at the level of the ischial spine and lesser sciatic foramen
type III – at the entrance of the pudendal canal (often associated with obturator internus spasm)
type IV – entrapment of terminal branches
Diagnosis
Pudendal nerve entrapment syndrome is primarily a clinical diagnosis. Imaging findings help identify extrinsic mass or lesions causing compressing of the pudendal nerve and characterizing the site of entrapment. Improving pain symptoms in response to a pudendal nerve block may also assist in confirming the diagnosis.
The Nantes criteria was published to facilitate the diagnosis of pudendal nerve entrapment 3.
Nantes criteria
Essential criteria:
pain in the territory of the pudendal nerve
pain primarily occurs in a seated position
pain does not wake the patient while sleeping at night
no objective loss of sensation
improvement in pain after pudendal nerve block
Complementary criteria:
neuropathic character of pain – burning, shooting or stabbing
presence of allodynia or hyperpathia
sensation of a foreign body in the rectum or vagina
pain increases throughout the day
unilateral pain
pain triggered after defecation
tenderness on palpation of the ischial spine
positive findings on neurophysiological testing in men and nulliparous women
Exclusion criteria:
pain exclusively in regions outside of the territory of the pudendal nerve
pruritis
exclusively paroxysmal pain
pain can be attributed to abnormal findings on imaging
Radiographic features
MRI
Inflammation of a compressed pudendal nerve may be demonstrated on T2 weighted MRI as edematous swelling and hyperintensity, in addition to kinking or a change in the thickness of the nerve 4.
MRI may also help characterize the location of pudendal nerve entrapment or identify any masses or lesions causing external nerve compression.
Ultrasound
High-resolution ultrasound may identify an increased cross-sectional area of the entrapped nerve compared to that of a healthy pudendal nerve, however this is an evolving application of ultrasound 5.
Treatment and prognosis
Conservative measures:
avoidance of exacerbating activities such as prolonged sitting
analgesia such as acetaminophen and NSAIDs, or neuroactive medications including amitriptyline, carbamazepine, gabapentin or pregabalin
management of bladder and bowel function to avoid pelvic straining
Physiotherapy:
exercises to achieve relaxation of the pelvic floor muscles
transcutaneous nerve stimulation (TENS) in combination with physiotherapy has been shown to improve pain and reduce analgesia requirements 6
Pudendal nerve block:
injection of a local anesthetic agent, often under the guidance of ultrasound to target the pudendal nerve at the lesser sciatic foramen 7
clinical improvement in response to a pudendal nerve block may confirm a diagnosis of pudendal neuralgia as the cause of symptoms
Surgery:
surgical decompression is a potential treatment for entrapment. There are several approaches with the primary goal of allowing complete mobility 7
Radiofrequency:
minimally invasive application of an electrical current into the site of the pudendal nerve to achieve either nerve ablation (continuous radiofrequency) or neuromodulation (pulsed radiofrequency) 8
Differential diagnosis
vulvodynia and vaginismus
chronic prostatitis
chronic pelvic pain syndrome
complex regional pain syndrome
shingles or superficial skin infections
external compression by tumor or mass
persistent genital arousal disorder or priapism
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