The ilioinguinal nerve is one of the branches of the lumbar plexus. It is a mixed nerve that arises as a continuation of the inferior branch of the anterior (ventral) ramus of spinal nerve L1.
The function of the ilioinguinal nerve is to provide the sensory innervation to the skin of the upper anteromedial thigh and partially the external genitalia. Moreover, it provides motor innervation to the internal abdominal oblique and transversus abdominis muscles.
This article will discuss the anatomy and function of the ilioinguinal nerve.
|Origin||Lumbar plexus (inferior branch of anterior ramus of spinal nerve L1)|
|Branches||Anterior labial nerves, anterior scrotal nerves|
Motor: Internal oblique muscle, transversus abdominis muscle
Sensory: Skin of proximal medial thigh, mons pubis, labium majus and root of the clitoris; anterior scrotum and root of the penis
- Origin and course
- Branches and function
- Anatomical variation
- Ilioinguinal nerve: Injury, entrapment and nerve block
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.
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.
Ilioinguinal nerve: Injury, entrapment and nerve block
The ilioinguinal nerve is susceptible to damage during abdominal surgery or from trauma to the abdominal wall. Injury to the ilioinguinal nerve can lead to a weakening of the transversus abdominus and internal oblique muscles, which can lead to the development of an inguinal hernia. Moreover, inguinal incisions carried out to repair inguinal hernias are a high-risk incision and may injure the ilioinguinal nerve. The nerve may also be damaged if it is included in the suture during incision closure causing nerve entrapment. Injury to the nerve can result in pain in the sensory distribution described above.
Both ilioinguinal nerve damage and entrapment during an inguinal hernia repair can lead to Post-Herniorraphy Pain Syndrome or inguinodynia, which is a chronic pain in the groin region lasting for greater than 3 months following inguinal hernia repair surgery, otherwise known as a herniorrhaphy. This can be treated with analgesia or physical therapy but these have been shown to have little effect. Ilioinguinal nerve block has been shown to be effective in reducing groin pain following herniorrhaphy. Nerve blocks can temporarily and reversibly block nerve transmission, leading to pain relief.
Local anesthesia administration between the layers of the transversus abdominus and internal oblique muscles, as well as between the internal oblique and external oblique muscles, can lead to temporary analgesia. The injection is placed 2cm medial and 2cm superior to the anterior superior iliac spine and can involve various chemical agents such as anesthetics, steroid, glycerol or alcohol.
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