Ultrasound-guided iliohypogastric nerve block is utilized as a diagnostic and therapeutic maneuver in the evaluation and treatment of groin pain thought to be mediated via the iliohypogastric nerve. The most common pain syndrome mediated via the iliohypogastric nerve is postoperative neuropathy secondary to surgical injuries to the iliohypogastric nerve during appendectomies and inguinal hernia repairs. Less commonly, iliohypogastric neuralgia can be seen in patients in their third trimester of pregnancy when a rapidly expanding abdomen causes a traction neuropathy of the nerve. The symptoms associated with iliohypogastric neuralgia depend on whether the main trunk of the nerve is damaged or if the injury is isolated to the anterior or the lateral branch of the nerve (Fig. 101.1). If the injury is isolated to the anterior branch of the iliohypogastric nerve, the patient will complain of burning pain, paresthesias, and numbness in the skin overlying the pubis. If the lateral branch is damaged, the patient will complain of burning pain, paresthesias, and numbness in the skin overlying the posterior lateral gluteal region. A Tinel sign may be elicited by tapping over the iliohypogastric nerve at the point where it pierces the transversus abdominis muscle.

Ultrasound-guided iliohypogastric nerve block can also be utilized to provide surgical anesthesia for groin surgery, including inguinal herniorrhaphy when combined with ultrasound-guided ilioinguinal and genitofemoral nerve block. Ultrasound-guided iliohypogastric nerve block with local anesthetics can be employed as a diagnostic maneuver when performing differential neural blockade on an anatomic basis to determine if the patient’s lower abdominal pain and groin pain are subserved by the iliohypogastric nerve. If destruction of the iliohypogastric nerve is being contemplated, ultrasoundguided iliohypogastric nerve block with local anesthetic can provide prognostic information as to the extent of motor and sensory deficit the patient will experience following nerve destruction.

Ultrasound-guided iliohypogastric nerve block with local anesthetic may also be used to provide postoperative pain relief following lower abdominal and groin surgeries and is useful in the treatment of persistent postoperative neuropathic pain following inguinal hernia surgery. Electromyography can distinguish iliohypogastric nerve entrapment from lumbar plexopathy, lumbar radiculopathy, and diabetic polyneuropathy. Plain radiographs of the hip and pelvis are indicated in all patients who present with iliohypogastric neuralgia to rule out occult bony pathology. Based on the patient’s clinical presentation, additional testing may be warranted, including a complete blood count, uric acid level, erythrocyte sedimentation rate, and antinuclear antibody testing. Magnetic resonance imaging of the lumbar plexus and retroperitoneum is indicated if tumor or hematoma is suspected (Fig. 101.2). The injection technique described later serves as both a diagnostic and a therapeutic maneuver.

The iliohypogastric nerve is derived from the L1 nerve root with a contribution from T12 in some patients. The nerve exits the lateral border of the psoas muscle to follow a curvilinear course that takes it from its origin of the L1 and occasionally T12 somatic nerves to inside the concavity of the ilium (Fig. 101.3). The iliohypogastric nerve continues in an anterior trajectory as it runs between the layers of the internal oblique and transversus abdominis muscles along with the ilioinguinal nerve and deep circumflex iliac artery (Fig. 101.4). It is at this point that the nerve can consistently be identified with ultrasound scanning and is amenable to ultrasound-guided nerve block. Within the fascial plane between the internal oblique and transversus abdominis muscles, the iliohypogastric nerve divides into an anterior and a lateral branch. The lateral branch provides cutaneous sensory innervation to the posterolateral gluteal region. The anterior branch pierces the external oblique muscle just beyond the anterior superior iliac spine to provide cutaneous sensory innervation to the abdominal skin above the pubis. The distribution of the sensory innervation of the iliohypogastric nerves varies from patient to patient due to considerable overlap with the ilioinguinal nerve. In most patients, the anterior branch of the iliohypogastric nerve provides sensory innervation to the skin overlying the pubis, with the lateral branch providing sensory innervation to the skin overlying posterolateral gluteal region (see Fig. 101.1).