The ilioinguinal nerve is a branch of the anterior rami of the L1 spinal nerve that originates in the lumbar plexus. Additionally, the iliohypogastric nerve is a branch of L1 that travels with the ilioinguinal nerve for a distance before branching off to a different destination and innervation. After exiting the lumbar plexus, the ilioinguinal nerve travels across the quadratus lumborum muscle as it courses laterally and crosses part of the liacus muscle as it approaches the iliac crest. It then wraps around anteriorly and pierces the transversus abdominis and internal oblique muscles. It then enters the inguinal canal and travels with the spermatic cord until it leaves the superficial inguinal ring entering its final destination sites.
The ilioinguinal nerve innervates the anterior surface of the scrotum or labia majora, root of the penis or mons pubis, and a small portion of the upper antero-medial thigh. It also innervates the internal oblique and transversus abdominis muscles.
This nerve (as well as the ilio-hypogastric nerve that it travels with) can be blocked as part of a TAP (Transversus Abdominis Plane) block with local anesthetic. The two branches of L1 travel together in the plane between the Internal Oblique and Transversus Abdominis muscles near the iliac crest and course anteriorly together. Using ultrasound, local anesthetic can be deposited in the plane to block the two nerves as well as several of the anterior branches of the intercostal nerves that supply the anterior portion of the abdomen.