Abdominal Cutaneous Nerve Entrapment Syndrome (ACNES)
One of the causes for chronic abdominal pain. Can lead to central sensitisation of the pain
Pain from the abdominal wall - hyperalgesia / allodynia / hyperaesthesia
Often points to lateral border of rectus abdominis
Entrapment of the cutaneous nerve due to:
(1) Sharp turning of the nerve through layers (neurovascular channels) of abdominal wall muscles
(2) Surgical scar tissue entrapment on the nerve (eg Abdominal wall hernia surgery)
(3) Injury to the nerve from surgical incision
Anatomy:
- Abdominal wall cutaneous nerves originate from ventral rami of T7 - T12
- 3 branches: Posterior branch ; Lateral branch ; Anterior branch
- Recall the landmark area:
- T10 at umbilicus level
- The nerves traverse between Internal Oblique Muscle (IOM) & Transverse Abdominalis (TA)
- The nerves continue anteriorly until behind the rectus abdominis.
- The anterior branch (most common to give rise to symptom): Opening / 'Sharp turn' of the nerve approximately at 0.5-1cm medial to the linea semilunaris (from posterior rectus sheath through the rectus abdominis into the skin, via a fibrous neurovascular channel)
Risk factors:
- Female
- Pregnancy (causes stretching of the muscle wall)
- Previous abdominal surgery
- Sports activity (that requires abdominal muscle contraction)
Clinical features:
- Well localised pain, often unilateral
- Neuropathic pain
- +/- Valleix phenomenon: Retrograde (circumferential) radiation of the pain (DDx Thoracic radiculopathy)
- Pain on movement (ie contraction of wall muscle => compression of nerve)
- Lying down may relief OR aggravate the pain
Examination:
- Carnett's sign
- Hover sign
- No pain on deep palpation (positive tenderness would indicate deep organ pathology)
- Pinch test
Ultrasound-guided injection/hydrodissection (Diagnostic & Therapeutic)
- Aim: Posterior rectus sheath
- 22-25G needle, LA+Steroid / 5% Dextrose water / Pulsed-RF / 50% Alcohol (less used nowadays)
- Scar-related ACNES: Hydrodissect the scar formation area with 5% Dextrose water
- Be mindful of (1) secondary nerve injury (2) the deeper structure - peritoneum
- Some may require multiple injections over a period of time
Other Rx:
- Rectus muscle stretching exercise
- Avoidance of triggering factor (eg certain exercise)
- Scar-related ACNES: Wall exercise to maintain normal gliding muscle movement
- Hot / Cold application
- Topical LA / Capsaicin cream
**T12/L1 nerve involvement may present with pain in scrotum / vulva
**Long list of DDx depending on level of involvement eg costochondritis
**Lateral branch and posterior branch can give rise to symptoms as well, but at different location. (less prone due to oblique orientation of the exiting nerve)
Reference:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6220638/
https://academic.oup.com/bjaed/article/15/2/60/248606
One of the causes for chronic abdominal pain. Can lead to central sensitisation of the pain
Pain from the abdominal wall - hyperalgesia / allodynia / hyperaesthesia
Often points to lateral border of rectus abdominis
Entrapment of the cutaneous nerve due to:
(1) Sharp turning of the nerve through layers (neurovascular channels) of abdominal wall muscles
(2) Surgical scar tissue entrapment on the nerve (eg Abdominal wall hernia surgery)
(3) Injury to the nerve from surgical incision
Anatomy:
- Abdominal wall cutaneous nerves originate from ventral rami of T7 - T12
- 3 branches: Posterior branch ; Lateral branch ; Anterior branch
- Recall the landmark area:
- T10 at umbilicus level
- The nerves traverse between Internal Oblique Muscle (IOM) & Transverse Abdominalis (TA)
- The nerves continue anteriorly until behind the rectus abdominis.
- The anterior branch (most common to give rise to symptom): Opening / 'Sharp turn' of the nerve approximately at 0.5-1cm medial to the linea semilunaris (from posterior rectus sheath through the rectus abdominis into the skin, via a fibrous neurovascular channel)
Risk factors:
- Female
- Pregnancy (causes stretching of the muscle wall)
- Previous abdominal surgery
- Sports activity (that requires abdominal muscle contraction)
Clinical features:
- Well localised pain, often unilateral
- Neuropathic pain
- +/- Valleix phenomenon: Retrograde (circumferential) radiation of the pain (DDx Thoracic radiculopathy)
- Pain on movement (ie contraction of wall muscle => compression of nerve)
- Lying down may relief OR aggravate the pain
Examination:
- Carnett's sign
- Hover sign
- No pain on deep palpation (positive tenderness would indicate deep organ pathology)
- Pinch test
Ultrasound-guided injection/hydrodissection (Diagnostic & Therapeutic)
- Aim: Posterior rectus sheath
- 22-25G needle, LA+Steroid / 5% Dextrose water / Pulsed-RF / 50% Alcohol (less used nowadays)
- Scar-related ACNES: Hydrodissect the scar formation area with 5% Dextrose water
- Be mindful of (1) secondary nerve injury (2) the deeper structure - peritoneum
- Some may require multiple injections over a period of time
Other Rx:
- Rectus muscle stretching exercise
- Avoidance of triggering factor (eg certain exercise)
- Scar-related ACNES: Wall exercise to maintain normal gliding muscle movement
- Hot / Cold application
- Topical LA / Capsaicin cream
**T12/L1 nerve involvement may present with pain in scrotum / vulva
**Long list of DDx depending on level of involvement eg costochondritis
**Lateral branch and posterior branch can give rise to symptoms as well, but at different location. (less prone due to oblique orientation of the exiting nerve)
Reference:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6220638/
https://academic.oup.com/bjaed/article/15/2/60/248606
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