Fecal incontinence
Fecal incontinence (FI), also known as anal incontinence, or in some forms encopresis, is a lack of control over defecation, leading to involuntary loss of bowel contents—including flatus (gas), liquid stool elements and mucus, or solid feces. FI is a sign or a symptom, not a diagnosis. Incontinence can result from different causes and might occur with either constipation or diarrhea. Continence is maintained by several interrelated factors, including the anal sampling mechanism, and usually there is more than one deficiency of these mechanisms for incontinence to develop. The most common causes are thought to be immediate or delayed damage from childbirth, complications from prior anorectal surgery (especially involving the anal sphincters or hemorrhoidal vascular cushions), altered bowel habits (e.g., caused by irritable bowel syndrome, Crohn's disease, ulcerative colitis, food intolerance, or constipation with overflow incontinence), and receptive anal sex. An estimated 2.2% of community dwelling adults are affected.
Fecal incontinence
The functioning of the anal canal can be damaged, traumatically or atraumatically. The resting tone of the anal canal is not the only factor which is important; both the length of the high pressure zone and its radial translation of force are required for continence. This means that even with normal anal canal pressure, focal defects such as the keyhole deformity can be the cause of substantial symptoms. External anal sphincter (EAS) dysfunction is associated with impaired voluntary control, whereas internal anal sphincter (IAS) dysfunction is associated with impaired fine tuning of fecal control. Lesions which mechanically interfere with, or prevent the complete closure of the anal canal can cause a liquid stool or mucous rectal discharge. Such lesions include piles (inflamed hemorrhoids), anal fissures, anal cancer or fistulae. Obstetric injury may tear the anal sphincters, and some of these injuries may be occult (undetected). The risk of injury is greatest when labor has been especially difficult or prolonged, when forceps are used, with higher birth weights or when an midline episiotomy is performed. Only when there is post operative investigation of FI such as endoanal ultrasound is the injury discovered. FI is a much under-reported complication of surgery. The IAS is easily damaged with an anal retractor (especially the Park's anal retractor), leading to reduced resting pressure postoperatively. Since the hemorrhoidal vascular cushions contribute 15% of the resting anal tone, surgeries involving these structures may affect continence status. Partial internal sphincterotomy, fistulotomy, anal stretch (Lord's operation), hemorrhoidectomy or transanal advancement flaps may all lead to FI post operatively, with soiling being far more common than solid FI. The "keyhole deformity" refers to scarring within the anal canal and is another cause of mucus leakage and minor incontinence. This defect is also described as a groove in the anal canal wall, and may occur after posterior midline fissurectomy or fistulotomy, or with lateral IAS defects. Rare causes of traumatic injury to the anal sphincters include military or traffic accidents complicated by pelvic fractures, spine injuries or perineal lacerations, insertion of foreign bodies in the rectum, and sexual abuse. Nontraumatic conditions causing anal sphincter weakness include scleroderma, damage to the pudendal nerves and IAS degeneration of unknown cause. Radiation induced FI may involve the anal canal as well as the rectum, when proctitis, anal fistula formation and diminished function of internal and external sphincter occur. Irradiation may occur during radiotherapy, e.g. for prostate cancer.