Background and indication: Local anesthetic block of the ilioinguinal and iliohypogastric nerves may be used as the primary intraoperative anesthetic for patients undergoing inguinal herniorrhaphy or perioperative pain management or for patients with chronic pain in the inguinal region. CadavEric studies have suggested that improved accuracy may be achieved using ultrasound techniques for blockade of these nerves.

Anatomy: The ilioinguinal and iliohypogastric are mixed sensory and motor nerves, formed from the ventral ramus of L1 with a lesser contribution from T12. As such, they typically arise from the upper portion of the lumbar plexus. Both nerves supply branches to the abdominal musculature. After passing through these muscles, they provide sensory innervation to the structures at their terminal locations. Thereby, the iliohypogastric nerve provides sensory innervation to the skin over the lower quadrant of the abdominal wall. Terminal branches of the ilioinguinal nerve also provide sensory innervation to the lower abdominal wall as well as the inguinal canal, the skin of the scrotum or labium majoris, the mons pubis, and the adjacent medial aspect of the thigh. The L1 ventral ramus enters the abdomen posterior to the medial arcuate ligaments and courses inferolaterally over the quadratus lumborum and posterior to the renal fascia. Near the iliac crest, it pierces the aponeurosis of the deepest of the three muscle layers of the abdominal wall, the transverse abdominal muscle. In this region, the single nerve splits into the ilioinguinal and the iliohypogastric nerves. Near the anterior superior iliac spine, both nerves pierce the middle muscular layer of the abdominal wall, the internal abdominal oblique muscle, as it fuses with transverse abdominis muscle. Hereon, the ilioinguinal and the iliohypogastric nerves continue their course between the internal and external abdominal oblique muscles, although the exact path may be fairly variable. The iliohypogastric nerve enters this muscle plane medially to the ilioinguinal nerve. It pierces the external oblique aponeurosis and terminates an average 4 cm lateral of midline. The ilioinguinal nerve begins its travel between the internal oblique and external oblique muscles just medially to the anterior superior iliac spine. It also courses medially, with its contributions to the lower abdominal wall ending 3 cm lateral to the midline. A continuation of the ilioinguinal nerve also courses inferiorly, passing through the external inguinal ring. The mean diameter of the ilioinguinal nerve among adults is 2.2 mm. High variation of the emergence and distribution of these nerves has been noted. The mean diameter of the iliohypogastric nerve is 2 mm. Using ultrasound imaging, they appear as oval hypoechoic areas with hyperechoic spots and are often in close proximity to a branch of the deep circumflex artery. The most consistent place to perform the block is at the level of the iliac crest where both nerves are lying between the internal oblique and transverse muscles.

Patient position: Supine. Lateral position is a better option for obese patients (abdominal wall will be displaced medially, decreasing needle-to-target depth).

Probe: A broadband linear array transducer. A curvilinear transducer may be necessary for obese individuals.