Anterior cutaneous nerve entrapment syndrome

Overview

Anterior Cutaneous Nerve Entrapment Syndrome (ACNES) is a frequently underdiagnosed cause of chronic abdominal wall pain. It occurs when small branches of the intercostal nerves (T7–T12), which pass through the abdominal wall muscles, become entrapped or compressed. This leads to localized, often sharp, abdominal pain unrelated to internal organ pathology.

Unlike visceral causes of abdominal pain, ACNES is a neuropathic pain syndrome that originates from the abdominal wall itself. It commonly affects young to middle-aged individuals and is more frequently reported in females.

Causes

The exact mechanism behind ACNES involves entrapment of the anterior cutaneous branches of the lower thoracic intercostal nerves as they pass through the abdominal fascia. Contributing factors may include:

• Minor abdominal trauma or strain

• Previous abdominal surgery or scarring

• Pregnancy or rapid weight changes

• Increased intra-abdominal pressure

• Repetitive motion or overuse of abdominal muscles

In many cases, no specific cause is identified.

Symptoms

ACNES presents with characteristic symptoms that distinguish it from visceral or spinal pain:

• Localized, sharp or burning pain in the lower abdominal wall, usually lateral to the midline

• Pain is often unilateral and worsens with movement, coughing, or prolonged sitting

• A distinct tender spot on the abdominal wall, usually less than 2 cm in diameter

• Positive Carnett’s sign: Pain intensifies when the patient tenses the abdominal muscles (e.g., lifting the head or legs while lying down)

• Hypersensitivity or altered sensation (hyperesthesia, hypoesthesia) over the affected area

The pain is typically chronic, lasting weeks to months, and may lead to unnecessary testing or surgery if not properly diagnosed.

Diagnosis

Diagnosis of ACNES is primarily clinical and based on a combination of physical examination and exclusion of other causes. Diagnostic steps include:

• Patient history and physical exam: Identification of a focal tender point and reproduction of pain with muscle contraction

• Carnett’s sign: Helps distinguish abdominal wall pain from intra-abdominal pathology

• Diagnostic nerve block: Injection of local anesthetic into the tender area can confirm the diagnosis if pain is temporarily relieved

• Imaging (ultrasound, CT, MRI): Typically normal, used to rule out other conditions

Treatment

Treatment of ACNES is usually conservative and often very effective:

Non-surgical Management:

• Local anesthetic injections: With or without corticosteroids; often repeated for sustained relief

• Physical therapy: Targeting the abdominal wall and posture

• Neuropathic pain medications: Such as gabapentin, pregabalin, or amitriptyline

• Topical analgesics: Including lidocaine patches or capsaicin cream

Surgical Management:

• Neurectomy: Surgical removal or release of the entrapped nerve may be considered in refractory cases

Prognosis

The prognosis for ACNES is generally favorable. Many patients experience significant or complete relief with local nerve blocks or conservative therapy. Early recognition and treatment are essential to avoid unnecessary surgeries or prolonged pain. For those who do not respond to conservative measures, surgical neurectomy has shown good long-term outcomes in selected patients.

Recurrence is possible but often manageable with repeat treatment.