The abdominal wall consists of the rectus abdominis, external oblique, internal oblique, and transversus abdominis muscles. The abdominal wall nerves control the majority of these core muscles and provide feeling to the abdominal skin and groin areas. Four major nerves are largely responsible for these actions, including the thoraco-abdominal (T7-T11), subcostal (T12), iliohypogastric (T12-L1), and ilioinguinal (L1) nerves. Abdominal wall pain can involve injury of any one of these nerves on the right or left side.
The symptoms of abdominal wall pain depend on the location of the injured nerve. Injury to the thoracoabdominal nerves (T7-T11) will result in symptoms higher up along the abdomen as compared to symptoms along the lower abdomen due to subcostal (T12) or iliohypogastric (T12-L1) nerve injury. Patients typically report a burning, electrical, or tingling type of pain in the affected area. Symptoms are often worse during nighttime and may awaken the patient in the morning. These symptoms are quite different than the cramp-like or colicky pain that is found with abdominal conditions such as appendicitis or gall stones.
Abdominal wall pain is typically caused by nerve damage. This may occur from tight anatomic structures, after surgical procedures such as laparoscopy, following trauma, or from radiation or a tumor. Depending on the situation, the nerve can be injured by compression, stretch, rupture, or direct damage. In entrapment injuries and some stretch-type injuries, the nerve can become compressed beneath tight anatomic structures such as fascia or muscle. In these situations, the nerve remains in continuity but is its outer lining can be damaged by the pressure caused by these tight structures. In rupture-type injuries, the nerve completely snaps and leaves two free ends that are no longer talking to each other. In direct damage, the nerve is injured by the negative effects of radiation or from a tumor invading it.
Abdominal wall pain can generally be diagnosed by the history of symptoms and physical exam. When the source of the pain is nerve damage, patients will report tenderness, electrical sensation, or tingling when tapping at known nerve sites. Improvement after injection with a numbing medicine and/or steroid further supports nerve damage as the source for the abdominal wall pain. MRI or ultrasound can sometimes be helpful for identifying the zone of injury.
Treatment of abdominal wall pain begins with medical management by a pain specialist. Patients are typically started on multiple medications targeting different aspects of their pain. Non-steroidal anti-inflammatory drugs, such as Naproxen or Ibuprofen, can also help reduce inflammation. Nerve-specific medications, such as Neurontin or Lyrica, can directly work on the injured nerve and lessen the electrical, burning, or tingling-like sensations. When oral medications fail to control the nerve pain, a pain specialist may perform a nerve block to turn off the pain signals that the injured nerve is sending back to the spinal cord. This is sometimes referred to as a stellate ganglion block.
If these measures fail to eliminate the abdominal wall pain, and there is an identifiable zone of nerve injury, surgery is sometimes recommended. Depending on the type of injury, the damaged nerve can be treated with either nerve decompression, nerve grafting, or targeted muscle reinnervation. For abdominal wall pain due to nerve compression, treatment includes a nerve decompression to provide enough space around the nerve. In situations of extensive damage to a critical nerve, nerve grafting is performed to remove the scar within the nerve and bridge it with nerve graft. Finally, for chronic nerve pain due to damage of a non-critical nerve, targeted muscle reinnervation is recommended. In this type of surgery the injured nerve is redirected to a local muscle so that the nerve is sending electrical signals to the muscle rather than back to the spinal cord. By doing so, the injured nerve is effectively tricked into talking with the muscle rather than signaling pain back to the spinal cord and brain.
Nerve decompression generally takes less than one-hour per surgical site and can be performed under general or wide awake local anesthesia. Nerve graft as well as targeted muscle reinnervation surgery can last several hours and are both performed under general anesthesia. After nerve decompression, patients are discharged home the same day on Tylenol, Motrin, and sometimes on a short course of narcotics. Light activity is encouraged when comfortable for the patient. One week after surgery, patients may take off their bandages and get the incision wet. Six weeks after surgery, patients may resume full activity. After nerve grafting or targeted muscle reinnervation surgery, patients may only need an overnight hospital stay and are discharged to home the following morning on Tylenol, Motrin, and a short course of narcotics. Three weeks after surgery, patients may take off their dressing. Twelve weeks after surgery, patients may resume full activity. Depending on the duration, intensity, and mechanism of damage for the nerve pain, relief may be immediate or can be more gradual and over the course of many months.