Iliohypogastric nerve

The iliohypogastric nerve is a mixed nerve that originates from the ventral ramus of the first lumbar nerve (L1). Occasionally, it also receives contributions from the ventral ramus of the twelfth thoracic nerve (T12) and rarely even from the eleventh thoracic nerve (T11).

The iliohypogastric nerve usually arises as a single trunk together with the ilioinguinal nerve (Read more!). This trunk is short and splits into two separate nerves upon reaching the lateral border of the psoas major muscle. Therefore, both these nerves arise from the ventral ramus of the first lumbar nerve (L1). Interestingly, in approximately 20% of cases, the iliohypogastric nerve is not present.

The iliohypogastric nerve, also known as the iliopubic nerve, innervates the skin overlying the iliac crest, gluteal region, and the inguinal and hypogastric regions. It also supplies a few anterolateral abdominal wall muscles (transversus abdominis and internal abdominal oblique muscle).

This nerve arises within the psoas major muscle and emerges from its upper lateral border before descending inferolaterally, passing obliquely above the iliac crest. It courses posterior to the lower portion of the kidney and anterior to the quadratus lumborum muscle (Read more!). The subcostal nerve (Read more!) runs superior and parallel to it, while the ilioinguinal nerve runs inferior and parallel. Usually, the iliohypogastric nerve gives off communicating branches to the ilioinguinal and subcostal nerves.

Approximately above the posterior third of the iliac crest, it pierces the transversus abdominis muscle. It then travels forward along the anterolateral abdominal wall, running between the transversus abdominis and internal abdominal oblique muscles about 0.59 inches (1.5 cm) above the iliac crest. Finally, it divides into two cutaneous branches - the anterior and lateral cutaneous branches.

• The anterior cutaneous branch passes anteriorly and medially between the internal abdominal oblique and transversus abdominis muscles. Approximately 0.79 inches (2 cm) medial to the anterior superior iliac spine, it pierces the internal abdominal oblique muscle. And approximately 1.18 inches (3 cm) above the superficial inguinal ring, it pierces the aponeurosis of the external abdominal oblique muscle. It is then distributed to the suprapubic skin as a cutaneous nerve, innervating the skin of the inguinal and pubic regions.
• The lateral cutaneous branch passes through the internal and external abdominal oblique muscles above the iliac crest. It is distributed to the skin of the posterolateral aspect of the gluteal region. It innervates the skin below the iliac crest and in the posterolateral gluteal region.

As mentioned before, the iliohypogastric nerve also provides muscular branches to the transversus abdominis and internal abdominal oblique muscles.

Note: If the pyramidalis muscle is present, the iliohypogastric nerve is the most likely source of its innervation.