Ilioinguinal Nerve Block

Indications and Clinical Considerations

Ilioinguinal nerve entrapment syndrome is caused by compression of the ilioinguinal nerve as it passes through the transversus abdominis muscle at the level of the anterior superior iliac spine ( Fig. 140.1 ). 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 nerve entrapment syndrome occurs spontaneously. Ilioinguinal nerve entrapment syndrome manifests as paresthesias, burning pain, and occasionally numbness over the lower abdomen that radiates into the scrotum or labia and sometimes into the inner upper thigh. The pain does not radiate below the knee. The pain of ilioinguinal nerve entrapment syndrome is made worse by extension of the lumbar spine, which puts traction on the nerve. Patients with ilioinguinal nerve entrapment syndrome often assume a bent-forward novice skier’s position. If the condition is not treated, progressive motor deficit consisting of bulging of the anterior abdominal wall muscles may occur. This bulging may be confused with inguinal hernia.

Physical findings include sensory deficit in the inner thigh, scrotum, or labia in the distribution of the ilioinguinal nerve. Weakness of the anterior abdominal wall musculature may be present. A Tinel sign may be elicited by tapping over the ilioinguinal nerve at the point at which it pierces the transversus abdominis muscle. As mentioned earlier, the patient may assume a bent-forward novice skier’s position ( Fig. 140.2 ). Lesions of the lumbar plexus from trauma, hematoma, tumor, diabetic neuropathy, or inflammation can mimic the pain, numbness, and weakness of ilioinguinal neuralgia and must be included in the differential diagnosis.

Electromyography helps distinguish ilioinguinal nerve entrapment from lumbar plexopathy, lumbar radiculopathy, and diabetic polyneuropathy. Plain radiographs of the hip and pelvis are indicated for all patients with ilioinguinal nerve entrapment syndrome to rule out occult bony disease. On the basis of the patient’s clinical presentation, additional testing may be indicated, including complete blood cell count, uric acid, sedimentation rate, and antinuclear antibody testing. Magnetic resonance imaging (MRI) of the lumbar plexus is indicated if tumor or hematoma is suggested. The injection technique described later serves as both a diagnostic and a therapeutic maneuver.

Clinically Relevant Anatomy

The ilioinguinal nerve is a branch of the L1 nerve root with contribution from T12 in some patients ( Fig. 140.3 ). The nerve follows a curvilinear course that takes it from its origin of the L1 and occasionally T12 somatic nerves to inside the concavity of the ilium. It continues anteriorly to perforate the transversus abdominis muscle at the level of the anterior superior iliac spine ( Fig. 140.4 ). The nerve may interconnect with the iliohypogastric nerve as it continues to pass along its course medially and inferiorly where it accompanies the spermatic cord through the inguinal ring and into the inguinal canal ( Fig. 140.5 ). The distribution of the sensory innervation of the ilioinguinal nerves varies from patient to patient because there may be considerable overlap with the iliohypogastric nerve. Generally, the ilioinguinal nerve provides sensory innervation to the upper portion of the skin of the inner thigh and the root of the penis and upper scrotum in men or the mons pubis and lateral labia in women (see Fig. 140.1 ).