Ilio-inguinal nerve

At a glance

English

Ilio-inguinal nerve

Latin (TA2)

Nervus ilioinguinalis

System

Nerve

Region

Abdomen

Side

Paired, left and right

About the ilio-inguinal nerve

The ilio-inguinal nerve is one of the lowest branches of the lumbar plexus. It comes from the anterior ramus of L1, leaving it together with the larger iliohypogastric nerve, and then follows a course parallel to and just below that nerve around the abdominal wall. Its job is mixed: it gives motor twigs to the deepest flat muscles of the lower abdomen and then becomes a cutaneous nerve of the groin and upper inner thigh.

The nerve first appears at the lateral edge of psoas major, a little below the iliohypogastric. From there it slants downwards and outwards across the front of quadratus lumborum and then over iliacus, lying behind the kidney and colon. Close to the front of the iliac crest it pierces transversus abdominis and enters the plane between that muscle and internal oblique, where it often exchanges fibres with the iliohypogastric nerve. Further forward it pierces internal oblique, supplying it on the way, and enters the inguinal canal.

Within the canal it lies on the spermatic cord or round ligament but outside their coverings. It never passes through the deep inguinal ring; it joins the canal partway along and leaves through the superficial ring to reach the skin. Its size is inversely related to that of the iliohypogastric nerve. When small it may end by merging with that nerve, which then sends a branch to take over its territory, and occasionally it is missing altogether.

Its position makes it vulnerable during groin surgery. It can be caught in sutures or mesh during inguinal hernia repair, or compressed after a low transverse incision, leaving burning pain or numbness over the groin and inner thigh. The same anatomy is used to advantage in an ilio-inguinal and iliohypogastric nerve block, in which local anaesthetic such as ropivacaine is placed between the abdominal muscle layers just medial to the anterior superior iliac spine to numb the area for hernia repair.

Course and supply

Arises from

The anterior ramus of L1, arising with the iliohypogastric nerve from the lumbar plexus and emerging at the lateral border of psoas major.

Ends in

Ends in cutaneous branches that leave the superficial inguinal ring to supply the skin of the groin and the upper, medial thigh.

Supplies

Motor to the lowest fibres of internal oblique and transversus abdominis; sensory to the upper medial thigh's skin and the adjoining groin.