Should we care about the internal anal sphincter?

Area of Science:

• Colorectal surgery
• Anorectal physiology
• Surgical anatomy

Background:

• The internal anal sphincter (IAS) is vital for maintaining fecal continence.
• Current surgical practices often involve IAS division, potentially leading to underestimated continence disturbances.
• Evidence supporting sphincter-sparing alternatives remains limited.

Purpose of the Study:

• To review physiological and morphological evidence supporting IAS preservation in anal surgery.
• To highlight the need for prospective data on sphincter-sparing techniques.
• To inform surgical decision-making in minor anorectal procedures.

Main Methods:

• Review of existing physiological and morphological data on the internal anal sphincter.
• Analysis of the rectoanal inhibitory reflex (RAIR) in incontinent versus normal cohorts.
• Examination of anatomical variations in external anal sphincter overlap.

Main Results:

• Continence disturbance incidence post-sphincterotomy may be underestimated.
• The RAIR demonstrates inherent differences suggesting IAS function as a continence defense.
• Anatomical variations may contraindicate IAS division in certain patients.
• IAS-preservation techniques in fistula surgery show potential for safeguarding function.

Conclusions:

• Prospective, randomized trials are essential to evaluate sphincter-sparing alternatives.
• Preoperative sphincter imaging and RAIR assessment are needed for informed surgical choices.
• Optimizing surgical techniques can potentially improve postoperative continence outcomes.