Fecal Incontinence and Anorectal Disorders
Anatomy and physiology
Continence relies on internal anal sphincter (IAS, smooth muscle, involuntary), external anal sphincter (EAS, striated, voluntary), puborectalis, rectal compliance, and stool consistency. The rectoanal inhibitory reflex (RAIR) allows sampling. Pudendal nerve (S2–S4) supplies EAS. Obstetric anal sphincter injury (OASI) is a major cause.
Evaluation
History (stool consistency, urgency, pad use), anorectal exam, endoanal ultrasound (sphincter defects), anal manometry (resting and squeeze pressures), and pudendal nerve studies. Distinguish passive soiling (IAS dysfunction) from urge incontinence (EAS/urgency).
Management
Conservative: dietary fiber, antidiarrheals (loperamide), pelvic floor muscle training, biofeedback. Surgical: sphincteroplasty for EAS defects, sacral neuromodulation for refractory cases, and in severe cases, graciloplasty or colostomy. Rectal prolapse and rectocele may contribute.
Traps
- Confusing passive soiling (IAS) with urge incontinence (EAS).
- Missing a sphincter defect on exam; endoanal ultrasound is key.
- Assuming all fecal incontinence is surgical; conservative therapy first.
- Overlooking rectal prolapse or impaction as a cause.
Rule of thumb
Stool consistency is a modifiable factor; fiber and antidiarrheals can dramatically improve symptoms. Consider sacral neuromodulation when conservative therapy and sphincter repair are inadequate.