Chronic Abdominal Wall Pain
Chronic abdominal pain of uncertain aetiology is a common clinical problem that often leads to many diagnostic evaluations and treatment interventions and sometimes multiple surgeries. Numerous reports have emphasized that patients with pain originating in the structures of the abdominal wall are frequently misdiagnosed and treated as suffering from visceral pain.
In 1926 Carnett, a surgeon, published the seminal article recognizing the syndrome that he believed was caused by intercostal neuralgia. Carnett’s test is a simple clinical test in which abdominal tenderness is evaluated while the patient tenses the abdominal muscles. It is useful for differentiating abdominal wall pain from intra-abdominal pain. When pain arises from an intra abdominal source, the tensed muscles in the abdominal wall guard the underlying bowel, thus reducing the discomfort (negative test). However, when the pain arises from the abdominal wall, the muscle contraction will accentuate the pain (positive test).
The most important cause of chronic abdominal wall pain is entrapment of a anterior cutaneous branch of one of the lower (T7-T12) intercostal nerves in its tortuous course through the abdominal wall muscle. After turning at a 90 degree angle, the nerve passes from the posterior sheath of the rectus abdominis muscle through a fibrous opening and then branches at right angles while passing through its anterior sheath. It has been thought that the underlying problem is nerve compression with resulting ischemia or lack of blood supply, explained by the nerve’s course through the muscle. Applegate termed the condition as “anterior cutaneous nerve entrapment syndrome” and suggested the entrapped nerve may also be pushed by intra- or extra-abdominal pressure or pulled by a scar causing pain in the abdominal wall.
Pain in the abdominal wall may arise from three or more sources, including:
- referral from abdominal or, less commonly, thoracic viscera because of neural convergence in the spinal cord from somatic and visceral sites
- T7– T12 radicular lesions
- peritoneal or abdominal wall lesions, most often nerve entrapment
Entrapment of the anterior cutaneous nerve appears to be the most common cause of chronic abdominal pain. Since 1972 Applegate and several other authors have hypothesized that the underlying lesion is nerve compression with resulting ischemia, explained by the nerve’ s course in relationship to the musculature. Other lesions affecting the nerve, including herpes zoster, tumors, or traumatic radiculitis, might cause similar findings by different mechanisms. Myofascial trigger points seem to be a less frequent explanation than nerve entrapment. Occasionally rectus sheath hematomas or small Spigelian (lineasemilunaris) or incisional hernias may be implicated. Epigastric hernias and“painful rib” (“ rib tip” or “ slipped rib” ) sometimes account for upper quadrant pain.