Ilioinguinal neuralgia is one of the most common causes of lower abdominal and pelvic pain encountered in clinical practice. Ilioinguinal neuralgia is caused by compression of the ilioinguinal nerve as it passes through the transverse abdominis muscle at the level of the anterior superior iliac spine. The most common causes of compression of the ilioinguinal nerve at this anatomic location involve injury to the nerve induced by trauma, including direct blunt trauma to the nerve, as well as damage during inguinal herniorrhaphy and pelvic surgery. Rarely, ilioinguinal neuralgia can occur spontaneously.
Ilioinguinal neuralgia is a common cause of groin or inguinal area pain. The ilioinguinal nerve can become entrapped after pelvic or hernia surgery, which can result in disabling pain in the inguinal area, lateral genitalia, or abdominal wall. The distribution and features of this pain can vary between patients, depending on anatomic variations in the course of the ilioinguinal nerve and the location of the entrapment. The pain can be diagnosed with nerve blocks and treated with nerve ablation using pulsed radiofrequency or neurectomy.
The ilioinguinal nerve (IIN) arises from the anterior ramus of L1 with some contributions from T12 and L2, similar to the iliohypogastric nerve (IHN), as part of the lumbar plexus. Emerging from the lateral border of the psoas major muscle, both nerves run subperitoneally in front of quadratus lumborum before piercing the transverse abdominis muscle above the iliac crest to become superficial. It pierces the internal oblique muscle mediocaudally to the anterior superior iliac spine (ASIS). The nerve enters the inguinal canal approximately 2 cm medial to the ASIS and exits through the superficial inguinal ring to function as a sensory nerve for the overlying skin. From there, it supplies innervation to the inner thigh and either scrotum or labia.
The IIN is commonly trapped at the rectus border, the iliac crest, and the paravertebral area. However, it can also be entrapped at the inguinal region, and patients with Pfannenstiel incisions or inguinal hernia repairs are at an increased risk for IIN entrapment anywhere between the ASIS and the pubis, due to tissue scarring or fibrosis. Hernia repair using mesh has a risk factor for entrapment of the IIN in the fibrotic tissue surrounding and adhering to the mesh.
The pain of ilioinguinal nerve entrapment is described as burning, sometimes accompanied by paresthesias or altered sensation, in the inguinal area and ipsilateral scrotum and testis/labia. It is commonly associated with surgical injury but it may occur spontaneously.
The pain pattern of the IIN can also mimic the pattern of the genitofemoral nerve. Patients with ilioinguinal neuralgia will complain of groin pain, which becomes worse with sitting, lifting, and bending. Benes et al. suggested using the term abdominoinguinal pain syndrome, to describe the combination of these nerve pathologies.
There are many conditions resulting in groin pain that mimic ilioinguinal entrapment, including inguinal hernia, tumor, varicocele, hydrocele, spermatocele, transient testicular or ovarian torsion, and myofascial injury.
Entrapment of the iliohypogastric or genitofemoral nerve needs to be included in the differential diagnosis as well. Other diseases that can clinically present with chronic inguinal pain (including hip osteoarthritis, disc herniation, recurrent inguinal hernia, and tumor) can be ruled out by selective radiological examinations including ultrasonography, computed tomography (CT), and magnetic resonance imaging (MRI).
Physiotherapy, TENS machine, acupuncture and mind–body therapies provide ways of ameliorating pain conditions and are important cornerstones in a multimodal approach.
Anti neuropathic drugs are likely to be the mainstay of management in ilioinguinal neuralgia. Opioids are second-line treatment alternatives but long-term use of opioids should be discouraged.
Ilioinguinal nerve block has been used for both diagnostic and therapeutic purposes in the diagnosis and treatment of ilioinguinal neuralgia. Historically, these nerve blocks were performed using a blind technique, using anatomic landmarks as guidance for needle placement.
Recent advances in ultrasound technology and its use in regional anesthesia have enabled practitioners to perform these blocks under a direct visualization, with successful outcomes reducing the risk of intraperitoneal needle placement and allowing for a smaller volume of injectate due to improved accuracy.
In a recent report by Thomassen et al the authors found ultrasound-guided nerve blocks to be effective in treating of ilioinguinal neuralgia with successful prolonged pain relief after a median follow-up time of 20 months.
If nerve blocks have been performed and provided significant analgesia but did not provide long-term relief, neuro ablative techniques such as chemical neurolysis, cryoablation, and pulsed radiofrequency (PRFL) ablation may be considered for a longer-lasting effect.
The use of pulsed radiofrequency ablation in the treatment of chronic post hernia repair pain has been reported in multiple case series as well as in a recent systematic review. PRF ablation delivers high-intensity currents in pulses, which allows for heat (typically 42°C) to dissipate during the latent phase so that neurodestructive temperatures are not obtained, thus lowering the risk of neuroma formation, neuritis-type reaction, and deafferentation pain. This mild heating of the nerve tissue is thought to temporarily block nerve conduction; however, the exact mechanism by which PRF ablation provides analgesia is unclear.
Pulsed radiofrequency treatment of ilioinguinal nerve under real-time ultrasound guidance can provide long-term pain relief in patients with ilioinguinal neuralgia.