Ultrasound-guided ilioinguinal nerve block is utilized as a diagnostic and therapeutic maneuver in the evaluation and treatment of groin pain thought to be mediated via the ilioinguinal nerve. The most common pain syndrome mediated via the ilioinguinal nerve is the entrapment neuropathy, ilioinguinal neuralgia. The patient suffering from ilioinguinal neuralgia will complain of burning pain, paresthesias, and numbness over the lower abdomen that radiates into the scrotum or labia and occasionally into the upper inner thigh, but never below the knee. Extension of the lumbar spine exacerbated the pain of ilioinguinal neuralgia, and the patient will often assume the novice skier’s position to relieve pressure on the affected nerve (Fig. 100.1). Untreated, the symptoms of ilioinguinal neuralgia often worsen with the motor impairment causing a bulging of the anterior abdominal wall, which may be misdiagnosed as an inguinal hernia. A Tinel sign may be elicited by tapping over the ilioinguinal nerve at the point where it pierces the transversus abdominis muscle.

Ultrasound-guided ilioinguinal nerve block can also be utilized to provide surgical anesthesia for groin surgery, including inguinal herniorrhaphy when combined with ultrasound-guided iliohypogastric and genitofemoral nerve block. Ultrasound-guided ilioinguinal 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 and groin pain are subserved by the ilioinguinal nerve. If destruction of the ilioinguinal nerve is being contemplated, ultrasound-guided ilioinguinal 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 ilioinguinal 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 ilioinguinal 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 ilioinguinal 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. 100.2). The injection technique described later serves as both a diagnostic and a therapeutic maneuver.

The ilioinguinal 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. 100.3). The ilioinguinal nerve continues in an anterior trajectory as it runs between the layers of the internal oblique and transversus abdominis muscles. It is at this point that the nerve can consistently be identified with ultrasound scanning and is amenable to ultrasound-guided nerve block. The ilioinguinal nerve then perforates the transverse abdominis muscle at the level of the anterior superior iliac spine, and its terminal branches provide sensory innervation to the skin over the inferior portion of the rectus abdominis muscle. The ilioinguinal nerve may interconnect with the iliohypogastric nerve as it continues to pass along its course medially and inferiorly, where it accompanies the genital branch of the genitofemoral nerve as well as the spermatic cord in men and the round ligament in women through the inguinal ring and into the inguinal canal. The distribution of the sensory innervation of the ilioinguinal nerves varies from patient to patient due to considerable overlap with the iliohypogastric nerve. In most patients, 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 (Fig. 100.4).

Ultrasound-guided ilioinguinal nerve block can be carried out by placing the patient in the supine position with the arms resting comfortably by the patient’s side (Fig. 100.5). A total of 7 mL of local anesthetic is drawn up in a 12-mL sterile syringe. If the painful condition being treated is thought to have an inflammatory component, 40 to 80 mg of depot steroid is added to the local anesthetic. The umbilicus, anterior superior iliac spine, and inguinal ligament are identified by visual inspection and palpation, and an imaginary line is drawn between the anterior superior iliac spine and the umbilicus (Fig. 100.6). A linear high-frequency ultrasound transducer is placed in a plane perpendicular with the inguinal ligament with the inferior aspect of the transducer lying over the anterior superior iliac spine and the superior aspect of the transducer pointed directly at the umbilicus, and an ultrasound survey scan is obtained (Fig. 100.7). The hyperechoic anterior superior iliac spine and its acoustic shadow are identified as are the external oblique, internal oblique, and transversus abdominis muscles, which extend outward from it (Fig. 100.8). The fascial plane between the internal oblique and transversus abdominis muscles is then identified, and the ilioinguinal nerve should be easily identifiable as an ovoid hypoechoic structure highlighted by a hyperechoic epineurium lying close to the anterior superior iliac spine (Fig. 100.9). The iliohypogastric nerve may also be seen lying medial to the ilioinguinal nerve in the same fascial plane (Fig. 100.10). Color Doppler may be used to aid



in identifying the fascial plane between the internal oblique and transversus abdominis muscles as this plane is also shared with the deep circumflex iliac artery (Fig. 100.11). When these anatomic structures are clearly identified on oblique ultrasound scan, the skin is prepped with anesthetic solution, and a 1½-inch, 22-gauge needle is advanced from the inferior border of the ultrasound transducer and advanced utilizing an in-plane approach with the trajectory being adjusted under real-time ultrasound guidance until the needle tip is resting within the internal oblique muscle (Fig. 100.12). At that point, after careful aspiration, a small amount of solution is injected under real-time ultrasound imaging to utilize hydrodissection to reconfirm the position of the needle tip. Once the position of the needle tip is reconfirmed, the needle is carefully advanced

through the deep fascia of the internal oblique muscle into the fascial plane between the internal oblique muscle and the transversus abdominis muscle in proximity to the previously identified ilioinguinal nerve. After careful aspiration, a small amount of solution is again injected to aid in identification of the exact position of the needle tip. After careful aspiration, the remainder of the solution is slowly injected under ultrasound guidance, which will demonstrate a bowing downward of the superficial fascia of the transversus abdominis muscle by the injectate. There should be minimal resistance to injection. The needle is then removed, and a sterile pressure dressing and ice pack are placed at the injection site.