Continuing Education Activity

Ilioinguinal neuralgia is a frequent cause of pain in the lower abdomen and the upper thigh commonly caused by entrapment or injury of the nerve after lower abdominal surgeries. The ilioinguinal nerve is responsible for motor innervation of the transverse abdominis and internal oblique muscles and provides sensory innervation to the upper anteromedial thigh region. In males, it also supplies sensory innervation to the anterior surface of the scrotum and root of the penis. In females, the ilioinguinal nerve supplies sensory innervation to the labia majora and mons pubis. Male or female patients with ilioinguinal neuralgia may complain of pain, paresthesia, and abnormal sensation in the area supplied by the nerve.

Diagnosis of ilioinguinal neuralgia requires a careful history, physical examination, electrophysiologic studies, and ultrasound examination. Treatment of ilioinguinal neuralgia usually starts with conservative measures. If conservative measures do not adequately control the symptoms, an ultrasound-guided nerve block, hydro-dissection, cryotherapy, or nerve radiofrequency ablation can generally provide satisfactory symptomatic relief. Resistant cases may require a neurectomy. This activity for healthcare professionals aims to enhance learners' competence in selecting appropriate diagnostic tests, managing ilioinguinal neuralgia, and fostering effective interprofessional teamwork to improve outcomes.

Objectives:

• Evaluate to exclude differential diagnoses of ilioinguinal neuralgia.

• Implement the recommended evidence-based evaluation strategies for ilioinguinal neuralgia.

• Determine the tailored management strategies for ilioinguinal neuralgia.

• Apply interprofessional team strategies to improve care coordination and patient outcomes.

Introduction

Ilioinguinal neuralgia is a frequent cause of pain in the lower abdomen and the upper thigh caused by an injury or damage to the nerve. The ilioinguinal nerve is a mixed nerve originating from the anterior rami of T12 and L1 nerve roots.[1] The nerve emerges near the lateral border of the psoas major muscle and goes inferior through the anterior abdominal wall, subperitoneal, and anterior to the quadratus lumborum muscle until it reaches the iliac crest.[1][2]

Then, the ilioinguinal nerve passes through the transverse abdominis and internal oblique muscles.[1] It becomes superficial after passing through the external inguinal ring anterior to the spermatic cord in males and the round ligament in females.[1] It gives motor innervation to the transverse abdominis and the internal oblique muscles.[1][2]

The ilioinguinal nerve also carries sensory information from the anterior surface of the scrotum and root of the penis in males or labia majora and mons pubis in females as well as a small area of the upper anteromedial thigh. Because of its long course, entrapment or injury of the ilioinguinal nerve after various lower abdomen surgeries is common, with both male and female patients complaining of varying degrees of pain, paresthesia, and abnormal sensation in the area it supplies.[1][2][3][4][5][6]

Diagnosis of ilioinguinal neuralgia requires a careful history, physical examination, electrophysiologic studies, and ultrasound examination. Treatment of ilioinguinal neuralgia usually starts with conservative measures, including oral analgesics, anticonvulsants, rehabilitation as electro-analgesic currents, and myofascial release.[1] If conservative measures do not adequately control the symptoms, an ultrasound-guided nerve block, hydro-dissection, cryotherapy, or nerve radiofrequency ablation can generally provide satisfactory symptomatic relief.[1] Resistant cases may require a neurectomy.[1][3][4][6]

Etiology

Iatrogenic and Traumatic Etiologies 

 The following procedures and conditions may result in ilioinguinal nerve injury, including:

• Abdominoplasty
• Appendectomy and hysterectomy, especially Pfannenstiel incisions
• Blunt abdominal trauma
• Femoral catheterization
• Inguinal hernia repair
• Lower external oblique aponeurosis disruption (eg, in hockey players) 
• Orchiectomy and testicular surgery using an inguinal approach
• Stretch trauma from pregnancy
• Traumatic trochar from laparoscopic surgery [2][4][5][7]

Idiopathic Nerve Entrapment

Nerve entrapments at the following sites often result from abnormalities in the musculoaponeurotic connective tissue due to tight fascial planes (see Image. Pelvic Nerves):

• Iliac crest
• Inguinal region
• Paravertebral area
• Rectus border muscle [8]

Epidemiology

Ilioinguinal neuralgia is a common cause of chronic lower abdominal and anterior pelvic pain. Ilioinguinal neuralgia is not uncommon following the surgical repair of an inguinal hernia but is rarely because of stretch or entrapment neuropathy.[9] There are about 800,000 hernia operations performed annually in the US, of which 12% result in chronic pain and 2% will develop significant ilioinguinal neuralgia.[1][10][11] The overall worldwide lifetime incidence of ilioinguinal neuralgia is reported to be as high as 18% to 24%.[12]

Pathophysiology

Chronic ilioinguinal pain can be caused by scarring from mesh, inflammation, nerve entrapment, a direct surgical injury, or thermal damage from cautery.[1] In cases of ilioinguinal nerve trauma, partial or complete transection can occur. If the nerve suffers a total transection, Wallerian degeneration may follow.[1]

Ilioinguinal nerve entrapment causes the nerve to become compressed and flattened. There is swelling proximal to the entrapment site. The entrapment can be due to scarring, inflammatory reactions with mesh, direct or indirect effects from suturing, staples, tissue or mesh folding, or compression/angulation with muscle layers, such as between the transverse abdominis and internal oblique muscles.[1][13][14] The net result is progressive ischemia of the nerve with resulting symptoms (see Image. Pathway of the Ilioinguinal Nerve).[15] 

History and Physical

Entrapment neuropathies are common disorders that can lead to significant disability. A correct diagnosis is essential for proper management. History taking and physical examination are the cornerstones of the diagnosis of ilioinguinal neuralgia.

Clinical History

Patients of ilioinguinal neuralgia complain of pain, commonly postsurgical, in the lateral aspect of the iliac fossa, lower abdomen, and upper thigh, as well as abnormal hyperesthesia or hypoesthesia in the cutaneous distribution of the ilioinguinal nerve.[1] Muscle weakness of the upper anterior medial thigh may also be noticed. Symptoms of ilioinguinal nerve neuralgia may include hyperesthesia or hypoesthesia of the skin along the inguinal ligament. The sensation may radiate to the lower abdomen and thigh but will not extend below the knee.[1] Pain may be localized to the medial groin, the labia majora or scrotum, and the inner thigh.[1] 

The characteristics of the pain may vary considerably. Patients often walk in a hunched-over or forward-flexed position as their discomfort worsens with hip extension due to stretching surrounding muscles and the ilioinguinal nerve.[1][16] A clear and specific traumatic event or surgical procedure can often be identified by patients as being associated with the start of their ilioinguinal neuropathy. Symptoms may appear immediately or take weeks, months, or even years to become apparent.[16] Additional symptoms suggestive of ilioinguinal neuralgia include the following:

• Hair loss and trophic changes in the anterior surface of the scrotum and root of the penis in males or labia majora and mons pubis in females.
• Hyperesthesia or hypoesthesia of a small area of the upper anteromedial thigh and the skin along the inguinal ligament.
• Pain in the medial groin, labia majora or scrotum, and inner thigh. Often clearly associated with a specific traumatic event or surgery.
• Pain may radiate to the lower abdomen. Up to 75% of patients will identify pain on light pressure to the external ring.
• The pain may also be reproduced by palpation immediately medial to the anterior superior iliac spine.
• Weakness of the muscles supplied by the ilioinguinal nerve (eg, in the upper anterior medial thigh). [15]

Physical Examination

On physical examination, there is tenderness on palpation, 1 in medial and inferior to the anterior superior iliac spine, or on direct pressure to the external ring on the affected side. A complete and comprehensive neurologic examination is mandatory to exclude genitofemoral and iliohypogastric neuralgia, lumbosacral radiculopathy, and plexopathy.[1][17]

Evaluation

Clinical features of a burning, stabbing pain and a finding of impaired sensation along the distribution of the ilioinguinal nerve are suggestive of an ilioinguinal neuralgia diagnosis.[1] This is confirmed by eliminating symptoms using an ilioinguinal local nerve block.[1][17][18] However, a negative response does not necessarily exclude the diagnosis of ilioinguinal neuropathy, as the effect of a local anesthetic can be delayed, blocked, or minimized by mesh-related fibrosis or inflammation.[19] The following methods are used in the evaluation of ilioinguinal neuralgia:

Clinical trial of a local anesthetic: A common method of confirming the diagnosis of ilioinguinal neuralgia is infiltrating the area of the ilioinguinal nerve with a local anesthetic and determining if the patient has relief from pain. This is frequently used as confirmation of the diagnosis of ilioinguinal neuralgia.[1][17][18]

Electrophysiologic studies: The benefit of the electrophysiologic examination for diagnosing an ilioinguinal nerve injury is questionable. Electrophysiologic studies are usually directed to help exclude lumbar radiculopathy and plexopathy.[6]

Magnetic resonance imaging: Magnetic resonance imaging (MRI) may be performed on the lumbosacral spine to exclude lumbar radiculopathies.[1]

Ultrasound imaging: Tracing the nerve starting from the psoas major border is difficult because of the small size and depth of the nerve, especially in obese patients.[20][21] Tracing the nerve at the iliac crest down to the external inguinal ring is much easier and can identify the cause of the entrapment, eg, the scar of a prior surgery.[21] A successful ultrasound-guided nerve block can confirm the diagnosis of ilioinguinal neuralgia.[20][21]

Treatment / Management

There are multiple strategies to treat chronic neuropathic groin pain.[17][22] The pain of neuropraxia is typically temporary and disappears with time. Sometimes, the chronic groin pain persists and interferes with the activities of daily living.[7]

Conservative Treatment

Conservative therapy should be initiated before other treatments as symptoms may be transient. Expectant management may be implemented if the pain and discomfort decrease over time. Additionally, various lifestyle modifications, such as avoidance of those activities that aggravate the symptoms of ilioinguinal neuralgia, should be applied, including prolonged walking, stooping, or hyperextension of the hip joint. A recumbent position, with flexion of the hip joint and thigh, tends to be the most comfortable and pain-free position.[23][24]

Oral analgesic medications are often used, such as nonsteroidal anti-inflammatory drugs (NSAIDs), opioids, antiepileptics, and antidepressants, including gabapentin, pregabalin, tricyclic antidepressants, selective serotonin-norepinephrine reuptake inhibitors, and conventional analgesics.[25][13] Lidocaine and capsaicin patches have not shown efficacy in randomized trials.[26][27] 

Rehabilitative measures include transcutaneous electric nerve stimulation, myofascial release, and acupuncture, which can control the symptoms of ilioinguinal neuralgia in some patients. Further therapy is needed if no improvement is noted after 6 months of conservative measures. Typically, patients are referred to pain management specialists at this point.[23][24]

Ultrasound-Guided Nerve Block

The goal of nerve blocks is to use local anesthetics, steroids, or some combination as an injection near the ilioinguinal nerve to interrupt neuronal transmission and relieve pain. The actual efficacy of nerve blocks is a bit unclear. Several studies show reasonable benefits in 55% to 75% of patients, but others demonstrated little to no relief.[1][28][29][30] Available studies are generally inadequate due to insufficient numbers, poor design, lack of control groups, and other deficiencies to definitively determine the true efficacy and safety of nerve blocks for chronic ilioinguinal neuralgia.[1][28] Nevertheless, nerve blocks remain a cornerstone of current therapy for the condition. The following technique should be performed during a nerve block:[1][20][31][32]

• Position the patient in the supine position.
• Use a linear probe with a 5 to 10 MHz frequency to obtain deeper muscle penetration.
• Place the probe transversely and start scanning from the anterior superior iliac spine.
• Visualize the nerve between the transversus abdominis and internal oblique muscles lateral to the inferior epigastric artery and the iliohypogastric nerve.
• Place the needle tip between the internal oblique and transverse abdominis muscle layers in the fascial plane.
• Introduce the needle from lateral to medial using an in-plane approach.
• As this space is very narrow, inject a small amount of normal saline to separate the layers and provide a better target.
• Identify the hyperechoic fascial sheaths of the internal oblique and transverse abdominis muscles, indicating proper space.
• Inject 10 to 20 mL of medication (eg, local anesthetic, steroids, or a combination) into this space.

Microwave Radiofrequency Nerve Ablation

Microwave radiofrequency ablation of the nerve appears to be a promising treatment modality for ilioinguinal neuralgia, especially when ultrasound guidance is used, as the therapy tip needs to be placed immediately adjacent to the nerve for the procedure to be successful.[33] In one study of 42 patients with ilioinguinal neuralgia and chronic pain, microwave nerve ablation provided substantially longer durations of pain relief of 12.5 months than nerve infiltration with local anesthetic, which lasted 1.6 months.[34] Another study of 10 patients showed that 83% had an average reduction of almost 70% in reported pain.[35][36][35]

Surgical Neurectomy

Surgical neurectomy is considered only after other available methods have failed or are unavailable. This means that cryotherapy, dorsal root ganglion stimulation, microwave nerve ablation, peripheral nerve stimulation, pulse radiofrequency ablation, and selective nerve root blocks should all be considered, if available, before resorting to this irreversible surgery.[37] In most cases, mesh and suture removal is also recommended.[38][7][39][38]

The procedure can be done open or laparoscopically or with a local anesthetic and sedation, allowing the patient to cooperate in nerve localization. Scarring and mesh implants can make exposure of the ilioinguinal nerve difficult. Nevertheless, surgical neurectomy is an effective treatment of last resort for patients who have failed all other curative treatments.[1] In most series, neurectomy provides substantial relief in most patients treated, although many patients report a return of pain over time.[40][41] A comprehensive literature review indicated excellent reported success rates of more than 70% with neurectomy for otherwise intractable chronic ilioinguinal pain.[7][39][38]

The surgery involves identifying and dissecting the ilioinguinal nerve proximal to the area of injury or entrapment. If possible, the entire length of the nerve is exposed and removed. Intraoperative neurectomy of the ilioinguinal nerve has been proposed as a prophylactic measure to prevent postoperative pain after tension-free mesh repairs. A meta-analysis of randomized controlled trials and multiple other studies have suggested this may effectively reduce postoperative morbidity.[42][43][44][45][46]

Additional Therapies 

• Cryotherapy: Freezing the nerve with ultrasound guidance has also been used to treat ilioinguinal neuralgia. Nerve degeneration is caused by severe endoneurial edema by creating ice crystals that damage the vasa nervorum.[1] The limited studies suggest it can relieve symptoms for 6 to 12 months, similar to microwave nerve ablation therapy.[47][48][49]

• Dorsal root ganglion stimulation: This procedure appears to be another promising treatment for ilioinguinal neuralgia pain. Several studies suggest reasonable efficacy of this treatment modality.[50][51][52][53][54][55] The SMASHING study, for example, demonstrated an average pain reduction of 50%, but lead dislocation and pain at the implantation site remained problems.[56]

• Peripheral nerve stimulation: This is another possible treatment option for otherwise intractable ilioinguinal neuralgia. Preliminary results in limited studies suggest durable pain relief, with most patients indicating satisfaction with the therapy. While it appears safe and effective, further studies are needed before this therapy can be routinely recommended.[57][58][59][60]

• Pulse radiofrequency ablation: In several small studies, ablation of the dorsal root ganglia has demonstrated good pain relief.[1][61][62][63] Larger studies of this promising treatment modality are needed to demonstrate long-term efficacy and safety.

• Selective nerve root blocks: Nerve blocks of T12 and L1 have been used successfully, but only in very few patients.[64]

Differential Diagnosis

A thorough history, physical examination, electrophysiologic studies, ultrasound examination, magnetic resonance imaging, and individual nerve block can help differentiate the exact cause of the lower abdomen and groin pain.[65] Differential diagnoses include:

• Femoral nerve neuralgia: This neuropathy can produce inguinal pain partly relieved with flexion and external hip rotation. There will be abnormal, uncomfortable sensations involving the anteromedial leg and anterior thigh. Patients will typically have difficulty walking and will notice their knees buckling in more severe cases. The saphenous nerve in the thigh is a branch of the femoral nerve and may be affected. If so, this will cause numbness along with knee pain. The saphenous nerve is purely sensory and will not cause weakness.
• Genitofemoral nerve neuralgia: This will typically produce a reduced sensation in the upper anterior thigh, just below the inguinal ligament on the affected side. Groin pain is common and worsens with light touch, hip rotation, and prolonged walking.
• Iliohypogastric nerve neuralgia: This condition is characterized by a sharp, burning pain that typically begins immediately after an abdominal surgical procedure. The pain is often described as a continuous burning or stabbing and generally extends from the surgical incision site into the suprapubic and inguinal areas. The discomfort may radiate to the scrotal or inguinal regions due to overlap with other cutaneous nerves. While the pain may start immediately after surgery, it can also be delayed by months or years. Scar tissue formation may be a factor, particularly in these cases of delayed symptom presentation. 
• Lateral femoral cutaneous nerve neuralgia: This neuropathy may include a burning or tingling sensation on the anterior and lateral aspects of the thigh. There may also be numbness. These symptoms typically increase when standing, walking, or extending the hip. They may also present when just lying prone. Sitting up generally relieves the symptoms.
• Lumbar plexopathy
• Lumbar radiculopathy
• Saphenous nerve neuralgia
• Varicocele
• Herpes Zoster
• Hydrocele
• Inguinal hernia

Prognosis

Chronicity of the pain after injury or entrapment of the ilioinguinal nerve is not uncommon. Fortunately, the majority of patients improve on their own or respond well to nerve blocks or surgical neurectomy.

However, some patients may continue to have burning pain for months or years. This pain is often unaffected by the usual analgesics. Such patients may require management by a pain specialist in such cases for treatment with nerve blocks or surgery.

Complications

Ilioinguinal blocks require a small injection volume, which significantly lowers the possibility of local anesthetic toxicity. Ultrasound guidance reduces the incidence of these complications. A complication common to all of these treatments is failure to relieve symptoms.

Complications of the non-steroidal anti-inflammatory drugs:[66][67][68]

• Gastritis
• Peptic ulcer
• Nephropathy
• Hepatotoxicity
• Hypertension
• Bleeding/thrombosis

Complications of the central painkillers (eg, gabapentin):[69]

• Ataxia
• Dizziness
• Fatigue
• Fever
• Nystagmus
• Peripheral edema
• Somnolence

 Complications of the nerve block:[70][71][72][73]

• Bleeding that causes hematomas or bruising
• Bowel perforation
• Infection
• Peripheral nerve injury or vascular injury
• Pelvic hematomas
• Temporary pain at the site of injection
• Transient femoral anesthesia 

 Complications of the neurectomy:[7]

• Hematoma
• Infection
• Seroma
• Testicular edema
• Tingling

Deterrence and Patient Education

The following factors should be discussed with patients when managing ilioinguinal neuralgia:

• Reduction of body weight
• Avoid positions and activities that precipitate pain
• Healthy nutrition

Pearls and Other Issues

It appears that performing an ilioinguinal nerve excision at the time of inguinal surgery (eg, an inguinal hernia repair) can reduce postsurgical pain and decrease the development of neuralgia to the point where some have advocated making this a routine part of inguinal surgery.[12][42][43][44][45] The diagnosis of ilioinguinal neuralgia is suggested by the following:

• Neuropathic pain, usually described as burning or stabbing, along the lateral border of the iliac fossa and radiates into the lower abdomen, upper inner thigh, and the median groin area, including the labia majora or scrotum.[1]
• Most patients can identify a specific precipitating event, such as a trauma or a surgical procedure that initiated the symptoms.[1]
• Favorable results from an ilioinguinal local nerve block usually confirm the diagnosis.[1][17][18]

Enhancing Healthcare Team Outcomes

Prevention of ilioinguinal neuralgia is possible. Surgeons should strive to avoid injury of the nerves near the field of the surgery and use mesh that doesn't induce fibrotic or severe inflammatory reactions. Consider performing a prophylactic neurectomy. The diagnosis and treatment of ilioinguinal neuralgia needs an interprofessional approach. Collaboration between physiatrists, neurologists, pain management physicians, and surgeons should direct an optimized approach to therapy to improve outcomes. Nurses and therapists should teach patients a healthy lifestyle to minimize pain and enhance the activities of daily living.

As the pain can be severe, it is best to involve the pain specialist and the pharmacist early. The pharmacist should educate the patient on pain medications and their adverse effects. The pain specialist may have to try a variety of medical and nonmedical measures to obtain pain relief. While some patients do get relief, a significant number of patients will have chronic pain that can affect their quality of life. Because the pain may lead to depression and anxiety, a mental health professional should be available as part of the healthcare team to counsel the patient.