The ilioinguinal nerve is a spinal nerve that starts in the low back, wraps around the lower abdominal muscles, and ends just underneath the groin. It is primarily responsible for transmitting pain and other sensations in the hip. When injured, however, the pain is often felt much more extensively, often in the inner thigh, groin, and genitals.
Location and Appearance
Almost any animal with a ribcage and legs has an ilioinguinal nerve connecting the lower back to the abdomen. In humans, it is the very first of many lumbar nerves.
When viewed in isolation, this nerve resembles a slightly misshapen loop. Beginning in the lower lumbar, it branches out in both directions, crossing over to the front of the body through the transversus abdominis muscle, a core abdominal muscle that extends from the hip to the rib cage. It ends just under the scrotum in males, and at the base of the vaginal opening in females.
The ilioinguinal nerve plays different roles in different places. When it first crosses through the abdominal muscles, for instance, it is instrumental in communicating with the iliohypogastric nerve. This nerve is what controls the diaphragm, which helps regulate breathing.
As it continues downward, the ilioinguinal nerve is responsible for transmitting sensations from the upper thighs and hips. Most of the feelings associated with hip movements and injuries are transmitted through it.
The nerve is also responsible for some sensation in the genitals. A great many nerves exist in this area, however, and the ilioinguinal nerve is not a primary player; arousal and sexual function, for instance, are part of a separate system. Still, it has an important role to play when it comes to basic sensations, like touch, pressure, and pain.
How the Nerve Sends Signals
The ilioinguinal loop is part of the afferent nervous system. Afferent nerves carry messages directly to the brain and the spinal cord. Neurons all along the length of the nerve transmit signals back to the lumbar connection, where they are routed up the spine to the part of the brain that deals with feeling and sensation.
The actual process of capturing and sending signals is relatively uniform across all nerves, the ilioinguinal nerve included. Nerves are tight bundles or neurons, each of which has a receptor. When stimulated, receptors are triggered to fire synapses, which nerves carry across their fibers to hubs at either end. The ilioinguinal's hubs are in the spine and in the groin region. Transmission works both to and from the brain, with that organ serving as the ultimate authority to decide whether the body should feel pain or other sensation.
How Injuries Happen
Most people remain unaware of their ilioinguinal nerve until it is injured. Injury is rare thanks to its relatively protected placement, however, and normal life activities do not usually expose it to risk.
Problems with this nerve are often the result of surgeries gone wrong. Appendectomies and hysterectomies are two of the most common procedures that bring the surgeon's knife very close to the nerve, though almost any surgery involving the lower abdomen or genitals can pose some risk. Nicking the nerve or injuring nearby muscles, causing scar tissue to grow across the nerve, can lead to a lot of pain and discomfort.
Injuries can also lead to ilioinguinal damage, particularly when they involve direct impact. This type of injury may be caused by things like sports accidents, car crashes, or falling and breaking a hip. In rare cases, the nerve can also be damaged in the third trimester of pregnancy. If woman's abdomen swells more than normal, the growing fetus can put tremendous pressure on the nerve. This condition is known as idiopathic iliohypogastric syndrome, and is estimated to occur in less than one in 1,000 pregnancies.
Diagnosing an ilioinguinal injury is often the most difficult part of treating a patient's pain. The nerve is almost never damaged in isolation, which means that many other things may be going wrong at the same time. Unless it has actually been severed, most nerve problems will usually fix themselves over time. Severed nerves usually require surgery, and even then will require a lot of time for recovery.
Nerve entrapment — when the nerve is trapped between muscles or scar tissue and is out of its normal placement — can sometimes be fixed manually, usually through deep massage or pressure. Physical therapy exercise programs involving stretching and tension release movements are also common.
For strains or other nerve damage, healthcare providers usually start with a high-powered pain medication. Depending on the extent of the injury, a standard painkiller is usually enough to provide relief while the nerve repairs itself. Patients who do not respond to general medication are typically prescribed a nerve block, which is a local injection that impairs the nerve's ability to fire pain synapses. Blocks are more invasive procedures, and are usually only temporary fixes.