Ilioinguinal nerve

Origin and course

The ilioinguinal nerve is a continuation of the anterior ramus of spinal nerve L1. In some cases, it may also receive contributions from the subcostal (T12) nerve or L2. Upon its origin, the nerve passes posterior to the psoas major and then emerges to the anterior surface of the quadratus lumborum. It continues obliquely downwards across its surface, passing also over the anterior surface of the iliacus muscle. Finally, at the level of the iliac crest, it pierces the transversus abdominis muscle.

After piercing the transversus abdominis, the ilioinguinal nerve also passes through the internal oblique muscle to enter the inguinal canal. In the canal, the nerve is located superficially to the spermatic cord.

The ilioinguinal nerve exits the inguinal canal through the superficial inguinal ring, after which it gives off its terminal sensory branches: the anterior scrotal/labial nerves which supply skin in the genital region. During its course through the inguinal canal, the ilioinguinal nerve can form various connections with the iliohypogastric nerve.

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Branches and function

The ilioinguinal nerve is a mixed nerve and gives off the following motor and sensory branches:

• Motor branches: Along its course over the posterior abdominal wall, the ilioinguinal nerve gives off motor branches that supply the transversus abdominis and internal oblique muscles.
• The anterior labial/scrotal nerves: After exiting the inguinal canal, the ilioinguinal nerve gives off the anterior labial nerve in females, and anterior scrotal nerves in males. The dermatome innervated by these branches includes the skin of the anterior 1/3 of the labium majus and the root of the clitoris (females), and skin of the anterior 1/3 of the scrotum and the root of the penis (in males).

Also, the ilioinguinal nerve innervates the skin of the proximal medial thigh.

Anatomical variation

The ilioinguinal nerve is smaller than the iliohypogastric nerve and is sometimes so small that it joins with the iliohypogastric nerve where it enters the quadratus lumborum. In this instance, a branch of the iliohypogastric nerve will then take its place. The ilioinguinal nerve can sometimes be absent and in this case, the iliohypogastric nerve will then supply its territory.