The iliohypogastric nerve is the name given to the first nerve of the lumbar part. It is equipped with both somatomotor and somatosensory fibers.
What is the iliohypogastric nerve?
The iliohypogastric nerve is a mixed nerve. It forms the first nerve of the lumbar plexus, also called the lumbosacral plexus. Its origin is in the lumbar segment L1 of the spinal cord. In some cases, it may also arise from the 12th thoracic segment (Th12). However, some anatomists do not include the iliohypogastric nerve in the lumbar plexus because its plexus character is considered insufficient. Thus, there is no exchange through it with the other segments of the spinal cord. The functions of the iliohypogastric nerve include innervation of the abdominal muscles as well as the skin within the hip region.
Anatomy and structure
The course of the iliohypogastric nerve begins above the ilioinguinal nerve. On the back of the psoas major (large lumbar) muscle, it runs on the quadratus lumborum muscle. After exiting the inguinal nerve at the lateral edge of the greater lumbar muscle, it arcs to the anterior surface of the quadratus lumborum muscle in the lateral direction. In doing so, it passes by the dorsal surface of the kidneys. It then passes through the transversus abdominis muscle (transverse abdominal muscle). Between the transverse abdominis muscle and the obliquus internus abdominis (internal oblique abdominal) muscle, the iliohypogastric nerve continues its path along the cranial surface of the crista iliaca (iliac crest). Approximately in the center of the crista iliaca, the sensory ramus cutaneus lateralis has its origin. The sensory terminal branch of the iliohypogastric nerve, called the ramus cutaneus anterior, takes its course parallel to the inguinal ligament (ligamentum inguinale) in the medial direction. Above the external inguinal ring (annulus inguinalis superficialis), it penetrates the tendon plate (aponeurosis) of the external oblique abdominal muscle (musculus obliquus externus abdominis). During the course of the iliohypogastric nerve into the center of the abdominal region, several branches are formed. These pass through the layers of the abdominal wall like cascades. In this way, the skin can also be reached by the nerve. In mammals equipped with seven lumbar vertebrae, such as carnivores, the first two lumbar nerves bear the designation nervi iliohypogastrici. They are subdivided into a cranial iliohypogastric nerve arising from segment L1 and a caudal iliohypogastric nerve arising from segment L2.
Function and Tasks
The central function of the iliohypogastric nerve is to supply the abdomen, which is done jointly with the ilioinguinal nerve. This involves motor supply to the abdominal muscles, whereas sensory innervation occurs in the abdominal skin. The supply is made by several branches. These are the rami musculares, the ramus cutaneus lateralis and the ramus cutaneus anterior. The rami musculares are delivered between the obliquus internus abdomis muscle as well as the transversus abdomis muscle. Their function is to supply the caudal portions of the two muscles. Through the ramus cutaneus lateralis, sensory innervation of the skin in the lateral hip region takes place. To some extent, the lateral gluteal region (gluteal region) is also supplied. In contrast, the ramus cutaneus anterior is responsible for the sensory supply of the skin at the inguinal ligament.
Diseases
Certain circumstances can cause damage to the iliohypogastric nerve. Thus, the nerve takes a dorsal course toward the kidney. For this reason, it is at risk of being affected during surgical procedures on the kidney. However, irritation of the iliohypogastric nerve in the region of the groin also often causes pain in the kidneys. In some cases, the iliohypogastric nerve is damaged by an enlargement of the kidney. At the same time, impairment of the ilioinguinal nerve is also in the realm of possibility, causing the affected person to experience pain in the groin area. If a proximal lesion of the iliohypogastric nerve and ilioinguinal nerve takes place, this may result in paralysis of the lower abdominal wall musculature. This also causes the abdominal wall to bulge hernia-like over the inguinal ligament. The protrusion is exacerbated when the patient stands or performs an abdominal press.Sensory deficits mainly affect the autonomic innervation areas. If the sensory end branches in the inguinal region are damaged, this leads to deficits in the thigh, inguinal and genital regions. However, the lateral hip region is spared. Worse than the sensory and motor deficits are the pronounced pains suffered by the affected person. These can be electric, stabbing or burning. Damage to the main trunk of the iliohypogastric nerve most commonly occurs from lesions of the lateral ramus cutaneus due to intramuscular injection or surgery to the iliac crest. Likewise, impairments due to nerve compression syndrome are conceivable. This involves chronic pressure damage to a nerve. In the case of the iliohypogastric nerve, this is manifested by chronic groin pain. Athletes are particularly affected by nerve compression syndrome. The diagnosis is considered difficult, however, because there are no other neurological complaints, such as sensory disturbances, in addition to the pain in entrapment syndrome. Nerve compression syndrome is usually triggered by intraoperative injuries to the nerve or scarring that occurs later. However, direct injuries to the abdominal wall due to sports accidents can also be responsible for the syndrome. Surgical neurectomy (nerve cutting) is considered the best treatment method. It shows the best results especially for the iliohypogastric nerve.
