Ilioinguinal nerve

The ilioinguinal nerve arises from the anterior ramus of the L1 nerve root from the lumbar plexus along with the iliohypogastric nerve. The predominantly sensory nerve eventually passes through the superficial inguinal ring to provide cutaneous sensation to the upper medial thigh, mons pubis and labium majus in women and to the root of the penis and anterior surface of the scrotum in men.

Gross anatomy

Origin

The ilioinguinal nerve arises with the iliohypogastric nerve as a single trunk from the anterior ramus of the L1 nerve root from the lumbar plexus. This trunk enters the abdomen behind the medial arcuate ligament and runs anterolaterally parallel and superior to the iliac crests traversing the anterior surface of the quadratus lumborum muscle. The common trunk is short and soon divides into the iliohypogastric and ilioinguinal nerves at the lateral edge of the psoas muscle. The ilioinguinal nerve is typically smaller than and inferior to the iliohypogastric nerve as it crosses the quadratus lumborum muscle.

Course

The ilioinguinal nerve runs parallel to and below the iliohypogastric nerve and has a slightly more oblique course as it traverses the anterior surface of the quadratus lumborum muscle. As it descends the nerve often crosses across the iliacus muscle. At the anterior end of the iliac crest the ilioinguinal nerve pierces the transversus abdominis and internal oblique muscles to enter the inguinal canal from the side, not through the deep ring. The nerve continues in the inguinal canal and exits at the superficial inguinal ring after piercing the external spermatic fascia to become subcutaneous.

Branches and supply

The ilioinguinal nerve provides cutaneous innervation to the superior medial thigh and:

• in men also supplies the skin over the anterior one-third of the scrotum and the root of the penis
• in women also supplies the skin over the anterior one-third of the labium majus and the root of the clitoris

The ilioinguinal nerve also gives off motor branches to muscle fibers of the internal oblique and transversus abdominis muscles which are inserted into the free edge of the conjoint tendon.

Relations

The ilioinguinal nerve travels inferiorly to the iliohypogastric nerve and has a more oblique course as it travels to the iliac crest, typically traversing the iliacus muscle. The ilioinguinal nerve accompanies the spermatic cord through the superficial inguinal ring.

Variant anatomy

Unlike the iliohypogastric nerve, the absence of the ilioinguinal nerve is rare, being absent in only 2.5% of lumbar plexus. Many variations have been described in the formation of the ilioinguinal nerve including formation from multiple roots and deriving branches from multiple spinal roots (most commonly T12 and L1).

The size of the ilioinguinal nerve is inversely proportional to the size of the iliohypogastric nerve.