Abdominal wall pain is a frequent cause of unexplained “tummy” pain — and the most common cause is anterior cutaneous nerve entrapment syndrome, or ACNES. It’s frequently overlooked because it’s mistaken for a problem inside the abdomen. So what is ACNES, and how do we diagnose and treat it?

What is ACNES?

ACNES is caused by the trapping of the small nerves that supply the skin of the abdominal wall. These nerves are the anterior cutaneous branches of the lower intercostal nerves (T7–T12). They pass between the abdominal muscles and turn sharply to reach the skin at the linea semilunaris — the junction between the rectus abdominis and the oblique muscles.

Trapping occurs where a nerve passes through a fibrous ring in the muscle. Common triggers include localised muscle scarring, a small fat hernia pushing into the ring, and weight gain from obesity or pregnancy. Repeated abdominal muscle tears can also lead to scarring and nerve trapping. 

anterior cutaneous nerve entrapment site

Symptoms of ACNES

ACNES pain has a characteristic pattern:

  • Localised — the pain sits at a single spot, which patients can often pinpoint with one fingertip
  • Dull or burning, with sharp exacerbations
  • Worse with movements that tense the abdominal wall, such as sitting up, bending, or twisting
  • Superficial — felt in the abdominal wall itself, not deep inside

The pain is usually on one side, and stays in the same place over time. This constancy helps distinguish it from pain arising from the abdominal organs.

How is ACNES diagnosed? 

The diagnosis is clinical, resting on the history and a key examination finding.

Carnett’s sign is the most useful test. We find the tender spot, then ask you to tense your abdominal wall by lifting your head or legs off the couch. In ACNES, the tenderness worsens when the muscles are tensed — a positive Carnett’s sign — because the pain comes from the wall itself. When abdominal pain comes from an internal organ, tensing the muscles usually reduces the tenderness. A positive Carnett’s sign strongly points to ACNES.

We often use ultrasound to look at the muscles and any scar tissue, and — importantly — to exclude other causes of abdominal wall pain such as a hernia. Further tests, such as an MRI or CT of the abdomen, help exclude problems with the abdominal organs or the thoracic spine.

Treatment of ACNES

Simple measures — ice, heat, and an abdominal support — help the symptoms, but they aren’t a long-term solution.

Ultrasound-guided injection: diagnostic and therapeutic

The mainstay of treatment is a targeted injection of local anaesthetic, usually with a small dose of cortisone, into the point where the nerve is trapped. This injection does two jobs at once. If your pain settles after the local anaesthetic, it confirms the diagnosis — the trapped nerve was the source. And the injection itself often treats the pain, sometimes for a prolonged period.

Placing that injection accurately matters, because the target is small and specific. Dr Masci injects under ultrasound guidance, which allows the local anaesthetic and cortisone to be delivered precisely to the entrapment point while avoiding the underlying abdominal cavity. Many people gain lasting relief from one or a small number of injections.

Other options

Where injections give only short-lived relief, further options include nerve medication such as amitriptyline, repeated injections, and — for resistant cases — a small surgical procedure (neurectomy) to remove the trapped terminal branch of the nerve.

Frequently asked questions about ACNE.S

How do I know if my abdominal pain is ACNES?

The clues are a pain you can cover with one fingertip, in the same spot each time, that’s worse when you tense your stomach and eased by rest. A positive Carnett’s sign — tenderness that increases when you lift your head or legs — makes ACNES likely. Normal blood tests and scans of the abdominal organs support it.

What is Carnett’s sign?

It’s the key examination test for ACNES. Tenderness that worsens when you tense the abdominal wall points to the wall itself as the source (a positive sign), whereas tenderness that eases on tensing points to an internal organ. It’s simple, quick, and reliable.

Does an injection cure ACNES?

Often it helps considerably. A local anaesthetic and cortisone injection at the entrapment point both confirms the diagnosis and treats the pain, and many people get lasting relief from one or a few injections. Where relief is short-lived, nerve medication or, rarely, a small operation is considered.

Is ACNES serious?

It’s not dangerous, but it can be genuinely debilitating and is often missed for a long time — people frequently undergo extensive tests for an internal cause before ACNES is recognised. The good news is that once diagnosed, it usually responds well to a targeted injection.

What else causes abdominal wall pain?

Other causes include a hernia, abdominal wall endometriosis, a rib-related problem, or referred pain from the thoracic spine. Ultrasound helps distinguish these, and excluding an internal-organ cause is an important first step.

Final word from Sport Doctor London about ACNES

Anterior cutaneous nerve entrapment syndrome is a common but frequently missed cause of chronic abdominal wall pain. The key is recognising the pattern — a pinpoint, one-sided pain with a positive Carnett’s sign — and confirming it with a targeted, ultrasound-guided local anaesthetic injection, which usually treats it at the same time. Most people improve without surgery.

If you have persistent, localised chronic abdominal wall pain, Dr Masci can assess you in London, including ultrasound in clinic. Contact the team here or call +44 (0) 203 488 0350.

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