Abstract
In our practice pudendal neuralgia is defined as pain in the area of innervation of pudendal nerve. Pudendal nerve entrapment is compression of the nerve by scar tissue, ligaments, or surgical material. Pudendal neuralgia may be caused by pudendal nerve entrapment, but other conditions described in this manual may lead to pudendal neuralgia. Diagnosis of pudendal nerve entrapment is difficult, and it is often made by exclusion of those other conditions leading to pudendal pain (pudendal neuralgia). Most patients with pudendal nerve entrapment have a traumatic event that causes the onset of pain. Pelvic MRI may be helpful in ruling out other conditions causing pain and CT-guided pudendal nerve blocks narrow down the diagnosis to the pudendal nerve. Conservative treatments include avoidance of nerve reinjury, physical therapy, nerve blocks, and oral medications such as gabapentin or pregabalin. Patients may also benefit from nerve ablation procedures (pulse radiofrequency and cryoablation) and nerve stimulators. For patients who have failed all the conservative treatments, surgical decompression is an option with good outcomes.
Editor’s Introduction
In our practice pudendal neuralgia is defined as pain in the area of innervation of pudendal nerve. Pudendal nerve entrapment is a compression of the nerve by scar tissue, ligaments, or surgical material. Pudendal neuralgia may be caused by pudendal nerve entrapment, but other conditions described in this manual may lead to pudendal neuralgia. Diagnosis of pudendal nerve entrapment is difficult, and it is often made by exclusion of other conditions leading to pudendal pain (pudendal neuralgia). Most patients with pudendal nerve entrapment have a traumatic event that caused the onset of pain. Pelvic MRI may be helpful in ruling out other conditions causing pain and CT-guided pudendal nerve blocks narrow down the diagnosis to the pudendal nerve. Conservative treatments include avoidance of nerve reinjury, physical therapy, nerve blocks, and oral medications such as gabapentin or pregabalin. Patients may also benefit from nerve ablation procedures (pulse radiofrequency and cryoablation) and nerve stimulators. For patients who have failed all the conservative treatments, surgical decompression is an option with good outcomes.
Introduction
Pudendal neuralgia is a severely painful and often disabling neuropathic condition in the dermatomal distribution of the pudendal nerve [1]. It can affect any individual, regardless of gender, leading to pain in the clitoris/penis, vagina/scrotum, perineum, and rectum. Pudendal neuralgia is caused by a direct or indirect injury of the pudendal nerve and is often seen in conjunction with other pelvic pain conditions such as irritable bowel syndrome (IBS), interstitial cystitis/bladder pain syndrome (IC/BPS), and pelvic floor tension myalgia. Since the genitals are primarily affected, pudendal neuralgia is often confused with IC/BPS, vulvodynia, vaginismus, and vestibulitis.
In this chapter, we will focus on pudendal neuralgia in patients with phenotypically female genitalia. The term pudendal neuralgia is defined as pain along the distribution of the pudendal nerve. In contrast, the term pudendal nerve entrapment is defined as compression of the pudendal nerve that is identified during surgical decompression.
Anatomy of the Pudendal Nerve
The pudendal nerve originates from the ventral rami of the second, third, and fourth sacral spinal nerves and carries motor, sensory, and autonomic fibers. Afferent fibers project onto thoracolumbar sympathetic and sacral parasympathetic systems, although exact pathways are not well understood. Effects are primarily inhibitory in the bladder, and thus suppress bladder overactivity [2]. In addition, the pudendal nerve is involved in physiological changes during sexual response through regulation of vaginal and clitoral blood flow [3]. The pudendal nerve carries motor innervation to the external anal sphincter, urethral sphincter, muscles of the urogenital triangle, and muscles of the pelvic floor. In 88% of cases, the levator ani muscles are primarily innervated by the pudendal nerve and often share innervation with nerves directly from the S3–S4 nerve roots [4]. Terminal branches of the pudendal nerve reach the skin of the clitoris, labia major/minora, vestibule, perineum, and anus. Therefore, neuralgia of the pudendal nerve may lead to burning/pain in these areas. It is important to note that many other nerves overlap with the pudendal nerve to innervate this dermatome, including the ilioinguinal nerve, genitofemoral nerve, and posterior femoral cutaneous nerve. (See Chapter 16.)
After the pudendal nerve arises from S2 to S4, it courses through the greater sciatic foramen ventral to the piriformis muscle and enters the interligamentous space, the area between the sacrotuberous ligament and sacrospinous ligament, where it is joined with the pudendal artery and vein. The nerve then bends around the sacrospinous ligament to enter the lesser sciatic foramen. At this point, it courses through Alcock’s canal, a narrow canal that is formed by the fascia of the obturator internus muscle. The canal ends at the medial aspect of the ischial tuberosity where typically three branches emerge: the inferior rectal, perineal, and dorsalclitoral nerves. The inferior rectal nerve travels medially and terminates at the external anal sphincter. The perineal branch courses ventrally along the inferior aspect of the inferior pubic ramus and stays superficial and caudal to the perineal membrane. It innervates the superficial transverse perineal, bulbocavernosus, and ischiocavernosus muscles. The dorsal/clitoral branch travels along the inferior edge of the inferior pubic ramus and may pierce the perineal membrane. It crosses either cephalad or caudad to the crus of the clitoris and then enters the crura of the clitoris on the dorsomedial side.
Anatomical Variations and Implications
The trunk of the pudendal nerve at the sacrospinous ligament has variability within the interligamentous space relative to the ischial spine. At that point, the pudendal nerve is a single trunk in 61.5% of cases and is divided into multiple trunks in 27% of cases [5]. The pudendal nerve fixed to the sacrospinous ligament by connective tissue. When dissected in an unembalmed cadaver, the nerve is mobile with hyperflexion of the hip, causing a lateral deviation at the sacrospinous ligament of 4 millimeters [6]. The degree of pudendal nerve mobility may have implications for postoperative recovery from pudendal nerve decompression.
The pudendal nerve is typically found 14.5–37 millimeters medial to the ischial spine. Therefore, performing a sacrospinous ligament fixation or placement of transvaginal mesh 3–4 centimeters from the ischial spine, as traditionally instructed, may lead to direct injury of the nerve.
The interligamentous space is narrow, measuring 10 millimeters, and can be further constricted by the falciform process of the sacrotuberous ligament that may be attached to the sacrospinous ligament. The pudendal nerve has been observed to also pierce the sacrospinous ligament and sacrotuberous ligament and its falciform process [7]. This narrow space and anatomical variance results in the interligamentous space to be the most common location of entrapment.
Alcock’s canal is variable in length and typically formed by the aponeurosis of the internal oblique muscle. The falciform process of the sacrotuberous ligament has also been observed to form Alcock’s canal by either terminating at the obturator fascia or extending along the ischial ramus, fusing with the obturator fascia and continuing toward the ischioanal fossa [8]. These findings have implications of the sacrotuberous ligament being involved in pudendal nerve entrapment.
The variability of the clitoral branch of the pudendal nerve along the inferior pubic ramus may be vulnerable to entrapment. The nerve may pierce the perineal membrane and is therefore susceptible to entrapment. Also, its proximity to the inferior pubic ramus may increase its susceptibility to injury against bone in the event of trauma.
Anatomical Considerations of Pudendal Nerve Entrapment
Along the course of pudendal nerve, entrapment may occur in areas of fixation, acute flexion, within narrow canals, and by dynamic forces. Common anatomical locations of compression listed from cephalad to caudad are
The piriformis muscle
Interligamentous space
Alcock’s canal
Ischial tuberosity
Inferior pubic ramus
The most common location of entrapment of the pudendal nerve is within the interligamentous space and Alcock’s canal. Compression of the nerve occurs when there are repetitive impact forces, acute direct trauma, or dynamic factors. Repetitive impact forces affect patients who develop pudendal nerve entrapment from activities such as cycling, where pressure from the bicycle seat at the perineum can cause nerve compression. Direct trauma is seen in patients following vaginal surgery, especially in reconstructive pelvic surgery that utilizes the sacrospinous ligament. Muscle spasms and dysfunction of the piriformis muscles and obturator internus muscle can lead to narrowing of the course of the pudendal nerve, leading to compression. Compression along the course of the pudendal nerve causes a narrowing that leads to increased pressure. Increased pressure can cause arterial compression, leading to ischemia, and venous compression leading to edema or congestion. These events result in the formation of fibrosis and entrapment. Intraoperatively, the pudendal nerve is seen fixed to the sacrospinous ligament with connective tissue. This observation should not be confused with nerve impingement but is an example of a physiological fixation that increases the susceptibility to injury.
Epidemiology
The prevalence of neuropathic pelvic pain has not been well defined, but has been estimated as 3.3% to 8.2% of the general population. It has been published that the prevalence of pudendal neuralgia is 1 in 100,000, but this is an estimate and not substantiated by any study. The portal for rare diseases (orphan.net) reports that the incidence in France is 1 in 6,000 people, updated in 2014 by Jean Jaque Labat. Prevalence of pudendal neuralgia may be much higher if the definition of “pain in the dermatomal distribution of the pudendal nerve” is used. This definition could include diagnoses such as vulvodynia, vaginismus, perineal pain, clitoral pain, and persistent sexual arousal disorder. Gender distribution can be estimated in studies of the reported outcomes of pudendal decompression surgery and other treatments. In these studies, women accounted for 60%–72% and men for 28%–40% of the study populations [9, 10]. Women may be more susceptible to developing pudendal neuralgia because of potentially traumatic events such as vaginal deliveries and vaginal surgery.
Etiology
Pudendal neuralgia can have somatic, visceral, and neuropathic origins and can be divided into pudendal neuralgia with and without entrapment. Somatic causes of pudendal neuralgia cause pudendal neuralgias via three mechanisms.
1. Hypertonic pelvic floor disorders may lead to symptoms of pudendal neuralgia without any true neuropathy. For instance, tension of the puborectalis muscle may lead to pain in the vagina and rectum with sitting.
2. Persistent hypertonicity can lead to peripheral sensitization of the pudendal nerve and neuralgia, and thus pudendal neuralgia without entrapment.
3. Pudendal neuralgia with entrapment can occur by muscle compression such as within Alcock’s canal by the obturator internus muscle or within the greater sciatic foramen by the piriformis muscle.
Visceral origins cause pudendal neuralgia via viscero-somatic convergence or referred pain. Patients with IBS, endometriosis, and IC/BPS have associated hypertonic pelvic floor disorders via viscero-somatic convergence. Hypertonic pelvic floor disorders can then lead to pudendal neuralgia as described earlier. Visceral pain or pathology of the cervix, lower uterine segment, and vagina may refer pain to the pudendal nerve from sympathetic splanchnic nerves and the superior hypogastric nerve plexus [11]. Indeed, the pudendal nerve also carries sympathetic fibers that are associated with bladder function, and therefore patients with IC/BPS may have associated pudendal neuralgia.
Neuropathic causes of pudendal neuralgia usually result from injury of the pudendal nerve. Peripheral nerve injuries from crushing, stretching, or infections can lead to neuropathy without entrapment. Entrapment can occur when injuries result in fibrosis or narrowing in the spaces along the course of the pudendal nerve. Nerve impingement can occur iatrogenically from surgery or from a mass effect. For example, impingement at the sacral nerve root from Tarlov cysts has also been described as a cause of pudendal neuralgia and persistent genital arousal disorders [12]. It is hypothesized that the hydrostatic pressure of the fluid within the cyst causes compression of the pudendal nerve root. Nevertheless, in a series of patients with pudendal neuralgia and MRI evidence of Tarlov cysts, location of the cyst did not correlate with laterality of symptoms.
Traumatic events are often associated with the onset of pudendal neuralgia. For example, cycling is a very well described mechanism of pudendal nerve injury via pressure from the narrow bicycle seat at the perineum. From a case series of more than 100 patients who underwent pudendal decompression, inciting events proposed by the authors were frequently related to repetitive activity or acute trauma. Repetitive activities, seen in 19% of patients, included prolonged sitting, new sedentary work, cycling, horseback riding, and other athletic/sports. Acute traumas were seen in 57% of patients and included vaginal surgery, vaginal deliveries, falls, and acute sports injuries. No inciting event was identified in 24% of cases.
Presentation
Pudendal neuralgia is characterized by a searing or burning sensation in the dermatomal distribution of the pudendal nerve. The hallmark symptom is neuropathic pain with sitting that is improved or alleviated by standing. Many patients have pain continuously, but sitting always exacerbates the pain. Pain may be bilateral or unilateral and may be localized to the clitoris, vagina, perineum, or rectum depending on which branch or branches are affected. Patients with pudendal nerve entrapment experience sharp stabbing pain in the vagina or rectum secondary to activation of the nervi nevorum (unmyelinated or poorly myelinated fibers that play a role in the transmission of evoked sensory information) of the pudendal nerve within the interligamentous space. Allodynia and hyperalgesia are common. This frequently leads to external pain with touch or pressure from clothing. Patients often experience an exaggerated pain response with exams or other touching. In rare cases, this sharp pain may be perceived in the right or left lower quadrant abdomen and be confused with visceral pathology.
Pudendal neuralgia has unique alleviating and aggravating factors. The pain is usually less severe in the morning and worse in the evening, but it does not wake up the patient at night. It is dependent on physical activity and sitting progressively worsen symptoms throughout the day. Sitting on a toilet seat alleviates the pain because pressure from the seat is focused the lateral aspects of the ischial tuberosities and allows for relaxation of the pelvic floor. Heat may improve somatic causes of pudendal neuralgia, while ice to the sacrum or vagina helps pain of neuropathic origin.
Associated symptoms include allotriesthesia, the sensation of a foreign object in the vagina or rectum, such as a ball. Some patients describe a sensation of a hot poker in those areas. Pudendal neuralgia prevents most patients from having sexual intercourse secondary to dyspareunia and postcoital pain that can persist for days. Bowel and bladder function may be affected, causing pain with a full bladder, urinary frequency and urgency, urinary hesitancy, dyschezia, and constipation.
Persistent genital arousal disorder (PGAD), sometimes referred to as restless genital syndrome, is one of the most vexing manifestations of pudendal neuralgia. Patients experience a physical sensation of arousal that is extremely unsettling and unrelenting. Masturbation and orgasm can temporarily alleviate symptoms, but, in some cases, these interventions can worsen the condition. It is not uncommon for patients with pudendal nerve entrapment to present with persistent genital arousal in the absence of pain. Therefore, patients with PGAD should be evaluated for possible pudendal neuralgia.
Without intervention, symptoms seem to worsen over time and patients begin to experience pain outside the dermatomal distribution of the pudendal nerve. Lower back, sacroiliac joints, lower abdomen, buttocks, and lower extremity are common areas of associated pain. Neuralgias may develop of the obturator, sciatic, posterior femoral cutaneous, and genitofemoral nerves. Pain outside of pudendal neuralgia in the setting of worsening pain may be a sign of central sensitization or complex regional pain syndrome. (See Chapter 2.)
This condition deeply affects patients’ social interactions and personal relationships and can lead to isolation, anxiety, and depression. The authors have found that validated quality of life questionnaires such as SF-36 scores of their patients are low in comparison to the general population. Patients with pudendal neuralgia are often disabled and unable to work. They need to spend most of the day lying down because sitting and other simple physical activities such as prolonged standing severely exacerbates their pain. It is difficult for significant others, family members, physicians, and other healthcare providers to understand the immense impact of pudendal neuralgia and chronic neuropathic pain. As a result, patients often endure poor support from others.
Diagnosis
History
Pudendal neuralgia is largely a clinical diagnosis based on history. It may be challenging to diagnose because patients may not explain their pain as described in the preceding section. Therefore, it is very important to ascertain the exact location of the pain. If patients localize their pain to the dermatomal distribution of the pudendal nerve, then the following questions can be used to screen for possible pudendal neuralgia.
1. Is your pain worse with sitting?
2. Do you feel better when sitting on a toilet seat?
3. Does your pain awaken you from sleep?
4. Do you feel your pain more on one side? *
5. Did your pain start after an accident, surgery, or physical activity?
*Although a patient with pudendal neuralgia may have bilateral symptoms, unilateral symptoms are highly indicative of nerve injury or neuropathic origin of pudendal neuralgia.
It is important to elicit when and how the symptoms started. Onset of symptoms related to an event such as surgery or falls may lead to speedier diagnosis and management. For instance, if the pain started immediately following a sacrospinous ligament fixation, it raises suspicion that a suture is impinging the nerve. This guides the physical examination, counseling, and subsequent management. A comprehensive review of systems and validated pelvic pain questionnaires should also be used in patients with pudendal neuralgia to identify associated conditions.
Physical Examination
The purpose of the physical examination is to [1] localize the pain to the distribution of the pudendal nerve [2], assess the pelvic floor muscles, and [3] refine the differential diagnosis.
Examination starts with general inspection, especially patient position, during history-taking. Patients often prefer to stand and may refuse to sit. Patients who are sitting may be leaning to their unaffected side or relieving pressure from their affected side by crossing their legs or sitting on their feet. Patients may sit on a cushion brought by them from home or may lie down throughout the interview.
Examination of the pudendal nerve is performed in the lithotomy position. First, the external genitalia are inspected and sensory testing should be performed. A cotton swab can be used to evaluate for allodynia and a filament used to evaluate for hyperalgesia. Sensory testing should include the entire vulva, perineum, anus, buttocks, thighs, groin, and mons pubis. A pain map can be drawn to identify the affected nerve (Figure 15.1). Unlike other peripheral nerve injuries, pudendal neuralgia rarely is associated with sensory deficit or numbness. Motor defects are similarly uncommon. Anal wink reflect should be elicited and sphincter tone noted. Pudendal neuralgia may cause autonomic dysfunction resulting in dryness of the skin and decreased sweat. Next, a single digit is introduced vaginally or rectally and the pudendal nerve is palpated at the sacrospinous ligament, along the obturator internus muscles, and along the inferior pubic ramus. Digital compression of the nerve at these sites may elicit a Tinel’s sign – pain at the site of examination with possible radiation of pain along the distribution of the nerve. Palpation of the nerve may reproduce symptoms such as genital arousal or foreign body sensation. Pelvic floor muscles should be palpated and muscle tension and tenderness noted. Reproducing pain with palpation of the muscle but not the nerve would suggest a pure muscle problem. Lastly, a full examination as discussed in [3] should be performed to develop a comprehensive differential diagnosis (Table 15.1). A particular focus on the musculoskeletal examination should be taken.
