Abdominal wall pain is a frequent cause of unexplained tummy pain. The most common cause of abdominal wall pain is anterior cutaneous nerve entrapment syndrome, or ACNES. What is ACNES syndrome, and how do we diagnose and treat it?  

What causes anterior cutaneous nerve entrapment syndrome? 

ACNES syndrome is caused by the trapping of the nerves supplying the skin of the abdominal wall. These tiny nerves pass between the abdominal wall muscles and enter the skin at the linea semilunaris aponeurosis at the junction between the rectus abdominis and oblique muscles. Trapping occurs due to localised muscle scarring, fat hernia protruding into the linea aspera, or weight gain due to obesity or pregnancy. Repeated abdominal muscle tears can sometimes lead to scarring and nerve trapping.  

anterior cutaneous nerve entrapment site

Anterior cutaneous nerve entrapment symptoms 

Generally, pain from ACNES syndrome has the following characteristics: 

  • Localised dull or burning pain with sharp exacerbations
  • Pain triggered by activities that contract the abdominal muscles, such as sit-ups, getting out of bed, coughing, sneezing or laughing, worsens pain. 
  • Lying flat improves symptoms.  

When your doctor examines you, they will find a localised area of tenderness or sensitivity at the linea aspera. Tapping the site of nerve trapping also reproduces pain. 

Doctors should exclude other causes of abdominal pain, including a fatty hernia, abdominal viscera pain (such as gallstones, appendicitis, diverticulitis), referred pain from the thoracic spine, slipping rib syndrome, or costochondritis. 

What is Carnett’s sign test? 

A positive Carnett’s sign is tenderness to pressure that worsens when the patient lifts their head or legs off the ground, increasing pressure on the abdominal wall. A positive test result increases the likelihood of ACNES syndrome. 

Ultrasound anterior cutaneous nerve entrapment syndrome

Often, we use ultrasound to visualise the muscles and scar tissue and exclude other causes of abdominal wall pain, such as a hernia. Further investigations, such as an MRI and CT scan of the abdomen, are helpful to exclude abdominal organ or thoracic spine pathology. 

Anterior cutaneous nerve entrapment treatment

Generally, simple treatments for anterior cutaneous nerve entrapment syndrome, such as ice, heat and an abdominal brace, can help with symptoms, although they are not a long-term solution. 

Nerve entrapment injections 

We usually resort to localised cortisone injections to confirm the diagnosis and treat symptoms. In general, we use ultrasound guidance to direct the injection into the area of nerve trapping at the linea semilunaris. Repeated injections can be performed for pain relief if the initial injection provides symptom improvement. 

In persistent cases, we can consider more permanent solutions, such as radiofrequency ablation or alcohol injection into the cutaneous nerves. Surgery in the form of release of the cutaneous nerves should only be reserved for persistent pain. 

Other causes of abdominal wall  pain

Diastasis recti

Diastasis recti is a condition characterised by the abnormal separation of the rectus muscles in the abdominal wall. It is common in women who have given birth. The separation often occurs during pregnancy, when the tissue between the rectus muscles stretches, causing a bulge in the abdominal contents and leading to abdominal coning. About a third of women still have abdominal doming one year after birth. However, we also see diastasis recti in men and athletes. 

Abdominal wall hernia 

An abdominal wall hernia presents as a small hole through which fat or abdominal wall contents protrude. A hernia can present with localised pain at the site of the hernia. 

Thoracic spine radiculopathy

Pain arising from the thoracic spine can radiate to the abdominal wall. If the thoracic spine nerves are trapped, pain may be accompanied by numbness and tingling in the abdomen. 

Final Word from Sportdoctorlondon regarding Anterior Cutaneous Nerve Entrapment Syndrome

We must consider anterior cutaneous nerve entrapment syndrome as a cause of unexplained abdominal pain. You should see a doctor with experience in diagnosing this condition. 

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