Principles of Neuropelveology
Marc Possover
Introduction
Neuropelveology is a new area in medicine which deals with the diagnosis and treatment of pathologies and dysfunctions of pelvic nerves. Neuropelveology encompasses knowledge that is for the most part already known but scattered in various other specialties. Neuropelveology brings all this knowledge into one. Since the establishment of the International Society of Neuropelveology, this discipline is experiencing a growing interest. In neuropelveology, fields of indications expand from management of pelvic neuropathic pain to pelvic nerve stimulation for management of pelvic organ dysfunctions and loss of functions in spinal cord-injured patients.
The potential novel treatment options not only have therapeutic value but also have preventive advantages, not only in the field of therapeutic medicine but also in preventive medicine with even future applications up to the “Mars mission” project.
The incidence of pelvic nerve pathologies is widely underestimated because of lack of awareness that such lesions may exist, lack of diagnosis and acceptance, and lack of declaration and report of such lesions. The most probable reasons for omission of the pelvic nerves in medicine are the complexity of the pelvic nerve system, the difficulties of etiologic diagnosis, and, probably the main reason, the limitations of access to the pelvic nerves for neurophysiologic explorations and neurosurgical treatments. Neurosurgical procedure techniques are well established in nerve lesions of the upper limb, but pelvic retroperitoneal areas and surgeries to the pelvic nerves are still unusual for neurosurgeons. Few open surgical approaches to the sacral plexus have been described by neurosurgeons for treatment of traumatic pelvic plexopathies, but these approaches are laborious and invasive, offer only limited access to the different pelvic regions, and expose patients to risk of severe vascular complications. Techniques of nerve neuromodulation to control pelvic pain syndromes and dysfunctions are for the same reasons limited to spinal cord and sacral nerve roots stimulation that considerably restrict their indications and effectiveness.
The use of the endoscope in combination with neurofunctional surgical procedures to the pelvic nerves proved to be a decisive advantage in this development,1,2,3,4 and in fact, it was the beginning of a new area in medicine: the neuropelveology.5,6,7 This specialty combines the knowledge required for a proper neurologic diagnosis, which is essential for an adapted treatment of intractable pelvic neuropathies. The concept of “neuropelveology,” the first medical practice focused on the pathologies of the pelvic nervous system was introduced more than 20 years ago by Possover. Since then, neuropelveology has established itself as a specialty in its own right, promulgated by the creation of the International Society of Neuropelveology in 2014.
Neuropelveology presents three consecutive aspects: the diagnostic stage followed by the therapeutic stage and the posttherapeutic follow-up of the patient.
The effort of neuropelveology focuses on these four major areas:
Diagnosis and treatment of pelvic neuropathic pain, with new techniques including laparoscopic pelvic nerves decompression and neurolysis
Treatment of pelvic organ dysfunction includes the stimulation of the genital nerves—GNS therapy
The technique of Laparoscopic Implantation Of Neuroprothesis to the pelvic nerves—LION procedure—for recovery of lost functions, especially in the spinal cord-injured patients and postsurgery pelvic nerve damage
The stimulation of the pelvic autonomic nervous system for prevention and/or treatment of general medical conditions such as osteoporosis, some cardiovascular diseases, or control of sarcopenia—process of aging
The diagnostic stage uses its own instruments and an anamnesis covering many aspects from gynecology, urology, orthopedics, pelvic vessel pathology, and psychology of chronic pain and parapleology. The clinical examination combines the examination of the pelvic organs and their function, the neurologic examination of the musculoskeletal system with a neuropelveologic examination, and the palpation of the pelvic nerves by vaginal or rectal route.8 Because somatic, neuropathic pain is more specific, neuropelveologic workup typically allows for specific diagnosis of the lesion site in the pelvic nerves.
Neuropelveology employs various medical treatments and surgical treatments of the pelvic nerves.
The latter includes neurosurgical techniques ranging from decompression, neurolysis, reconstruction, and even nerve resection (e.g., sciatic nerve endometriosis) to pelvic neurofunctional surgery.
The latter includes neurosurgical techniques ranging from decompression, neurolysis, reconstruction, and even nerve resection (e.g., sciatic nerve endometriosis) to pelvic neurofunctional surgery.
Because the pelvic nerves contain not only afferent but also efferent fibers involved in sexual function, voiding and storage of the bladder, as well as defecatory function, pelvic nerve damage lead to pelvic organ dysfunctions.
PELVIC NEUROFUNCTIONAL ANATOMY
The innervation of the pelvis is very complex. Sensory and motor nerves are found in the pelvis; the sensory nerve fibers send information to the brain (afferent), or vice versa (efferent), and the motor nerves divide into the following nerves:
The somatic nerves, which innervate the skeletal muscles (voluntary, or red, muscles). These nerves originate in the ventral roots of the spinal cord. The main somatic pelvic nerves involved in pelvic organ functions originate from the sacral plexus and its branches.
FIGURE 18.1 Sacral plexus. (Reprinted from Agur AM, Dalley AF. Grant’s atlas of anatomy, 15th ed. Philadelphia: Wolters Kluwer, 2021.)
The autonomic nerves, which innervate the glands and the smooth muscles (involuntary, or white muscles). These nerves divide into sympathetic nerves (ventral roots of spinal nerves T1-L2) and the parasympathetic nerves (ventral roots of spinal nerves S2-S4/S5).
This division is of great importance in understanding neural anatomy and is essential in understanding management of pelvic pain conditions in neuropelveology. Neuropathic pain as well as functional disorders of the pelvic organs must be considered together. In daily medical practice, the more information there is, the more confusing the situation usually becomes. In neuropelveology, it is exactly the opposite: The more information there is, the easier it is to determine the affected nerve(s) and the anatomical location of the damage. This reminds us of the crucial importance of a thorough history where all the information, even the smallest detail is important.
The sacral plexus (Fig. 18.1) is formed from the lumbosacral trunk and the ventral rami of sacral nerve roots S1-S4/S5. L5 is mainly involved in the dorsal flexion of the ankle (lesion → foot drop), whereas S1 mediates
the plantar flexion of the ankle and consequently the Achilles reflex.
the plantar flexion of the ankle and consequently the Achilles reflex.
If laparoscopic electrical stimulation of the sacral nerves root is used intraoperatively via laparoscopic neuro-navigation technique, S4 electrical stimulation does not produce any motoric action in the lower extremities, whereas stimulation of S3 nerves is confirmed visually by a deepening and flattening of the buttock groove (bellows reflex/anal wink) as well as a plantar dorsiflexion of the large toe and, to a lesser extent, of the smaller toes. Stimulation of S2 produces an outward rotation of the leg and plantar flexion of the foot as well as a clamp-like squeeze of the anal sphincter from the anterior to the posterior.
The branches of the sacral plexus are:
The superior gluteal nerve emerges from the lumbosacral trunk about 2 cm above the greater sciatic notch and leaves the pelvis through the greater sciatic foramen above the piriformis, accompanied by the superior gluteal artery and the superior gluteal vein. This small nerve is extremely important for the stability of the pelvis because it supplies the gluteus medius, the gluteus minimus, and the tensor fasciae latae muscles.
The pudendal nerve is a sensory and somatic nerve that originates from the ventral rami of the 2nd to 4th (and occasionally 5th) sacral nerve roots. After branching from the sacral plexus just proximal to the sacrospinous ligament, the nerve leaves the pelvis through the greater sciatic notch, reenters the pelvic cavity through the lesser sciatic notch, and finally travels to three main regions: the gluteal region, the pudendal canal, and the perineum. It accompanies the internal pudendal vessels upward and forward along the lateral wall of the ischiorectal fossa, being contained in a sheath of the obturator fascia termed the pudendal canal (Alcock canal). The pudendal nerve gives off three distal branches: the inferior rectal nerve, the perineal nerve, and the dorsal nerve of the penis (in males) or the dorsal nerve of the clitoris (in females) (DNP). The pudendal nerve carries sensation from the external genitalia of both sexes and the skin around the anus and perineum as well the motor supply to various pelvic muscles, including the external urethral sphincter and the external anal sphincter. As the bladder fills, the pudendal nerve activates. Contraction of the external sphincter, coupled with that of the internal sphincter, maintains urethral pressure (resistance) higher than normal bladder pressure. The storage phase of the urinary bladder can be switched to the voiding phase either involuntarily (reflexively) or voluntarily.
The pudendal nerve then causes relaxation of the levator ani so that the pelvic floor muscle relaxes. The pudendal nerve also signals the external sphincter to open. The sympathetic nerves send a message to the internal sphincter to contract, resulting in a higher urethral resistance. The pudendal nerve is also known to have a potential modulatory effect on bladder function. Somatic afferent fibers of the pudendal nerve are thought to project on the sympathetic thoracolumbar neurons to the bladder neck and modulate their function. This neuromodulation effect works exclusively at the spinal level and appears to be at least partly responsible for bladder neck competence and urinary continence. Pudendal supply is not significant in the vaginal wall because there is no striated muscle, but efferent supply largely from the pudendal nerve controls the levator muscle that provides support for and influences the function of the lower third of the vagina (Fig. 18.2).
The pelvic splanchnic nerves (parasympathetic) (Fig. 18.3): the preganglionic fibers that lead out of the sacral nerve roots S2-S4/S5. The pelvic splanchnic nerves transfix the sacral hypogastric fascia, where they form a meshwork of five to seven smaller nerves after sprouting out from different orientations. A medial group of fibers crosses the pararectal space tangentially and anastomoses to the pelvic plexus at the posterolateral aspect of the rectum. The more lateral fibers are more vertical and anastomose to the pelvic plexus ventrally at the level of the bladder pillar laterally and caudally to the urethrovesical junction. From a surgical point of view, the best way to expose the pelvic splanchnic nerves consists of first exposing sacral nerves S3-S4 laterally to the sacral hypogastric fascia and then following them ventrally until the nerves emerge from the roots. The pelvic splanchnic nerves regulate the emptying of the urinary bladder, control opening and closing of the internal urethral sphincter, influence motility in the rectum, and influence sexual functions such as erection.
Sympathetic pelvic innervation
The sympathetic innervation of the pelvis (Fig. 18.4) originates from:
The sympathetic trunk which stretches on both sides of the spine as a uniform nerve fiber-ganglion cord. The trunk part of the sympathetic trunk joins up with the lumbar and sacral parts. Both lumbar trunks run directly along the medial insertion of the iliopsoas muscle, ventral to the lumbar veins, and have approximately four associated neural ganglia. Anatomically, the left sympathetic trunk lies beside aorta, whereas the right sympathetic trunk remains hidden behind the inferior vena cava and can only be damaged by a retrocaval lymphadenectomy. Damage to the lumbalis of the sympathetic trunk typically leads to homolateral peripheral vasodilation and a warming up of the homolateral foot. The sacral part of the sympathetic trunk runs along the sacrum medial to the sacral foramens. It normally consists of three sacral ganglia that form fibers ventral to the sacrum of the opposite ganglia and show anastomosis to the inferior hypogastric plexus (IHP).
FIGURE 18.2 Pelvic side wall view of sacral and coccygeal nerve plexuses. (Reprinted from Agur AM, Dalley AF. Grant’s atlas of anatomy, 15th ed. Philadelphia: Wolters Kluwer, 2021.)
The IHP (or so called plexus pelvicus). Different plexuses originate from the vegetative solar plexus, orientate themselves along the various collaterals of the aorta, and innervate all the abdominal organs. One of these plexuses is the intermesenteric plexus, which runs ventrolaterally to the aorta between both mesenteric arteries and forms the inferior mesenteric plexus. This plexus dispatches branches that partly accompany the mesenteric arteries and branches that run between the inferior mesenteric artery and the aorta. At the level of the 5th lumbar vertebrae or ventral of the promontorium, the superior hypogastric plexus divides into two inferior hypogastric nerves that run downward into the mesorectum, ventral to the Waldeyer fascia. At the level of the pelvis, the sympathetic fibers build on both the rectum and the IHP. The IHP (also known as the knot from Lee, hypogastric knot, or plexus pelvicus) lies deep in the pelvis in the superior pelvirectal space, lateral to the rectum and the craniodorsal part of the vagina. The plexus shows itself as a net of fibers that form a sacrouterine ligament, also called a rectovaginal pillar.
 FIGURE 18.3 Pelvic autonomic nervous plexus. |
The lumbar plexus (Fig. 18.5) is formed by the divisions of the first four lumbar nerves (L1-L4) and from contributions of the subcostal nerve (T12), which is the last thoracic nerve. Additionally, the ventral rami of the 4th lumbar nerve pass communicating branches, the lumbosacral trunk, to the sacral plexus. Several branches of the lumbar plexus run into the pelvis.
 FIGURE 18.4 Sympathic and parasympathetic innervation of the pelvic organs. |
The iliohypogastric nerve runs anterior to the psoas major on its proximal lateral border, laterally and obliquely on the anterior side of quadratus lumborum. Lateral to this muscle, it pierces the transversus abdominis to run above the iliac crest. It gives several motor branches to these muscles and a sensory branch to skin of lateral hip. Its terminal branch then runs parallel to the inguinal ligament to exit the aponeurosis of the abdominal external oblique above the inguinal ring, where it supplies the skin above the inguinal ligament with the anterior cutaneous branch.
The ilioinguinal nerve runs on the quadratus lumborum caudally to the iliohypogastric nerve. At the level of iliac crest, it pierces the lateral abdominal wall and runs medially at the level of the inguinal ligament, where it supplies motor branches to the transverse abdominis and sensory branches through the external inguinal ring to the skin over the pubic symphysis and the lateral aspect of the labia majora.
The genitofemoral nerve originates from upper part of the lumbar plexus, pierces the psoas major
anteriorly below the iliohypogastric and ilioinguinal nerves, then immediately splits into two branches that run downward on the anterior side of the muscles, lateral to the external iliac artery. The lateral femoral branch is purely sensory and supplies the skin below the inguinal ligament and proximal lateral aspect of the femoral triangle. The genital branch runs in the inguinal canal together with the round ligament. It then sends sensory branches to the skin of the mons pubis and the labia majora.
FIGURE 18.5 Lumbosacral plexus. (Reprinted from Possover M. Neuropelveology: Latest developments in pelvic neurofunctional surgery. Germany: International Society of Neuropelveology, 2015.)
The lateral cutaneous femoral nerve pierces the psoas major on its lateral side and runs obliquely downward below the iliac fascia. Medial to the anterior superior iliac spine, it leaves the pelvic area through the lateral muscular lacuna. In the thigh, it briefly passes under the fascia lata before it breaches the fascia and supplies the skin of the anterior and lateral aspects of the thigh. Injury to the lateral femoral cutaneous nerve can cause anterior and lateral thigh burning, tingling, and/or numbness that increases with standing, walking, or hip extension.
The obturator nerve descends behind the psoas major, then follows the linea terminalis into the lesser pelvis lateral to the external vessels, and then finally leaves the pelvis through the obturator canal. In the thigh, it sends motor branches mainly to the adductor muscles. The anterior branch contributes a terminal sensory branch, which supplies the skin on the medial distal part of the thigh. Obturator nerve injury causes loss of thigh adduction. It is commonly injured during retroperitoneal surgeries for malignancies or endometriosis. It presents with sensory loss in the upper medial thigh and motor weakness in the hip adductors. It can also be injured during paravaginal repairs or transobturator sling placement. The anatomical relationship of the obturator nerve to transobturator tapes can be as close as 2.5 cm away from anterior branch.
The femoral nerve is the largest branch of the lumbar plexus. It provides considerable sensory innervation to the anterior aspect of the thigh and knee and motor innervation to the quadriceps muscles. The femoral nerve runs in a groove between the psoas major and iliacus, giving off branches to both muscles, and exits the pelvis through the medial aspect of the muscular lacuna. In the thigh, it divides into numerous sensory and muscular branches and the saphenous nerve, its long sensory terminal branches, which continues down to the foot. Femoral neuropathy is the most common lumbosacral nerve injury at the time of pelvic surgery. Patients typically report falling when attempting to get out of bed after surgery. In addition to difficulty ambulating, they may also report sensory loss over the anteromedial thigh. The femoral nerve commonly can be compressed by self-retaining retractors as it exits from the psoas muscle, and it can be compressed under the inguinal ligament if the thighs are hyperflexed.
Nerve Injuries during Gynecologic Surgeries
Injuries to the lumbosacral plexus can occur up to 2% at the time of gynecologic surgeries. All the approaches of gynecologic surgeries (vaginal/laparoscopic/laparotomy) can cause nerve injury.
Nerve injuries during pelvic surgery can occur due to compression, stretching, and transection.
TABLE 18.1 Mechanism of Nerve Injury during Gynecologic Procedures | |||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Compression and stretch injuries can cause mild demyelinating injuries, which recover quickly. They can occasionally result in injury to the nerve fiber or axon. Axonal injuries take longer to recover.
Fortunately, majority of nerve injuries spontaneously resolve. Knowledge of the basic neural anatomy is essential for understanding the nerve injury during surgery (Table 18.1). Nerve fibers are divided into fascicles and are surrounded by loose connective tissue (Fig. 18.6).
Such characteristics along with the elasticity of perineurium protect the nerve fibers from injury caused by compression and stretch forces.
Such characteristics along with the elasticity of perineurium protect the nerve fibers from injury caused by compression and stretch forces.
 FIGURE 18.6 Peripheral nerve. (Reprinted from Handa VL, Van Le L. Te Linde’s operative gynecology, 12th ed. Philadelphia: Wolters Kluwer, 2020.) |
The Seddon classification is used to classify nerve injuries. This classification helps the surgeon to anticipate patient’s prognosis and recovery.
Neurapraxia (local conduction block): The injury is caused by transient nerve ischemia. There is no injury to axons and Schwann cells. This type of injury is similar to when the foot falls asleep. Usually, the resolution is within minutes unless the injury is longer causing demyelination.
Axonotmesis (axonal injury with preservation of the protecting Schwann cells): It can affect sensory, motor, and autonomic nerves. Wallerian degeneration begins within 1 to 2 days after injury. Axons grow at 1 mm/day, and typically, these injuries take weeks to months until full recovery.
Neurotmesis (complete disruption of the axon, Schwann cell, and connective tissue): It is caused by complete transection of the nerves. Surgical intervention is required for resolution.
COMMON CONDITIONS
Bladder Hypersensitivity (Increased Bladder Sensation)
Hypersensitive bladder symptoms are defined as increased bladder sensation, usually associated with urinary frequency and nocturia, with or without bladder pain. Hypersensitivity of the bladder occurs due to an activation of the sensory nerves of the bladder located either in the IHP (which contains afferents fibers originating from the inferior hypogastric nerves and the sympathetic trunks) or in the sacral nerve roots S2-S4, the pudendal nerve, and the DNP. In the first situation, bladder hypersensitivity is associated with visceral pelvic pain, the latter with pelvic somatic pain symptoms.
Pathologies of the inferior hypogastric plexus
The endometriosis of the uterosacral ligaments is a common gynecologic etiology for hypersensitivity of the bladder. Because the disease infiltrates mainly the cranial portion of the IHP that supplies the organs of the pelvis,2 hypersensitivity of the bladder is associated with visceral pelvic pain, dysmenorrhea, rectal disorders (“irritable colon”), and deep dyspareunia. Because pelvic sympathetic afferent fibers rise upward to the superior hypogastric plexus by crossing the promontory to the solar plexus, pelvic symptoms are associated with ascending back pain and multiple vegetative symptoms affecting the whole vegetative nervous system (Table 18.2). Clinical examination focuses on specific clinical details for vegetative disorders such as pupil dilation, salivation inhibition, and tachycardia.
The second classical etiology, which is widely underestimated, is surgical damage of the IHP secondary to prolapse surgeries, radical pelvic surgery for malignancies, or deeply infiltrating endometriosis.9,10,11
TABLE 18.2 Visceral versus Somatic Pain: Symptoms | |||||||||||||||
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