Aetiology
Functional faecal incontinence associated with chronic constipation and severe faecal impaction
The child has no underlying anatomical abnormality, but the severe faecal impaction leads to dilation of the rectum.
Chronic dilation leads to decreased rectal sensation, so the child has less urge to defecate.
Softer stool forms above the hard impaction, and the softer stool leaks around the hard stool, known as 'overflow'.[1]
Functional non-retentive faecal incontinence
The exact aetiology is unknown, but possible contributing factors include psychological, behavioural, or emotional disturbances, genetics, and decreased motor function and sensation in the gastrointestinal tract.
Aetiology is likely to be multi-factorial.[10]
Organic faecal incontinence
Anatomical abnormalities of the gastrointestinal tract or neurological denervation of the gastrointestinal tract leads to inability to control bowel movements.[11]
The child has either an underlying anatomical abnormality (e.g., anorectal malformations, spinal and neurological abnormalities, or post-surgical abnormality) that causes the lack of bowel control, or a medical condition (e.g., hypothyroidism, coeliac disease, or cystic fibrosis) that may result in faecal impaction with overflow incontinence.
Medication overuse
Rarely, faecal incontinence may be due to overuse of medication (i.e., laxatives or orlistat) used mainly by adolescents and adults.
Pathophysiology
Faecal continence requires normal gastrointestinal and neurological structures and functions involved in the proper functioning of anal sphincters, muscles, and nerves controlling the gastrointestinal tract. Any underlying process that disturbs the normal functioning of the anatomical structures involved in maintaining faecal continence will cause faecal incontinence.
Functional faecal incontinence associated with chronic constipation and severe faecal impaction: a cycle of constipation and the formation of large, painful bowel movements leads to manoeuvres to prevent defecation, such as tightening of gluteal muscles. Faecal impaction of hard stool results, and softer stool flows around the impacted faecal mass and leaks from the distended rectum, which is desensitised to the sensation of needing to defecate.
Functional non-retentive faecal incontinence: the exact pathophysiology is unknown but, by definition, the child does not have faecal retention or an inflammatory, anatomical, metabolic, or neoplastic process that explains the faecal incontinence.[1]
Organic faecal incontinence: the exact aetiology of faecal incontinence depends on the underlying cause. Examples include the following:
Anorectal malformations are associated with abnormal puborectal musculature and anal sphincters, and abnormal anal sensation.
Children with spinal and neurological abnormalities may also have dysfunctional bowel motility and abnormal anal sensation.[3]
Faecal incontinence following surgery for Hirschsprung's disease may be secondary to resultant abnormal sphincter function, abnormal sensation, loss of recto-colonic inhibitory reflex, or overflow incontinence due to constipation.[12]
Hypothyroidism may result in chronic constipation with subsequent faecal retention and overflow incontinence.
In children presenting with a more recent onset of constipation and faecal retention, anal fissure may be a contributing factor to the continued constipation.
Cystic fibrosis and coeliac disease may present with increased stool frequency and diarrhoea.
Classification
Functional faecal incontinence associated with chronic constipation and severe faecal impaction
The child has no underlying anatomical abnormality but experiences overflow soiling due to chronic constipation and severe faecal impaction.[1]
Functional non-retentive faecal incontinence
The child has no faecal impaction or underlying anatomical abnormality or medical condition and experiences faecal incontinence for unclear reasons.[1]
Organic faecal incontinence
The child has an underlying anatomical abnormality (e.g., anorectal malformations, spinal and neurological abnormalities, or post-surgical abnormality) or medical condition (e.g., hypothyroidism) that causes the lack of bowel control.[2][3]
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