The corrugator cutis ani is a layer of smooth muscle fibres in the perianal subcutaneous fat that radiates from the anal verge to produce the corrugated, puckered appearance of the perianal skin. Unlike most other sphincter components, it is a smooth muscle and therefore operates involuntarily. It contributes to the fine-grained sealing of the anal verge at the distal end of the continence mechanism.
| Origin | Subcutaneous fibres of the perianal skin surrounding the anus |
|---|---|
| Insertion | Perianal skin in a radiating pattern around the anal verge |
| Nerve Supply | Inferior rectal nerve (from pudendal nerve, S2-S4) |
| Blood Supply | Inferior rectal artery |
| Actions | Produces the characteristic radial wrinkling of the perianal skin, assisting anal closure |
|---|
Assessment of the corrugator cutis ani reflex, observed as the characteristic wrinkling of the perianal skin in response to gentle pin-prick of the perianal skin, tests the integrity of the S2-S4 reflex arc (the anocutaneous reflex). Loss of this reflex indicates lower sacral cord or pudendal nerve dysfunction. Surgical procedures in the perianal region, including haemorrhoidectomy and fistulotomy, may damage the fine dermal fibres producing a smooth rather than corrugated anal appearance.
Assessed visually as the radiating skin wrinkles around the anal verge at rest, and dynamically by the anocutaneous reflex produced by gentle stroking of the perianal skin.
Absence of the corrugator ani reflex wrinkling response to perianal skin stimulation indicates impaired S2-S4 afferent or efferent arc integrity, seen in cauda equina syndrome, pelvic floor denervation, and sacral nerve injuries, providing a quick bedside test of lower sacral function.
