Incomplete evacuation of feces leading to the formation of a large, firm, immovable mass of stool in the rectum or distal sigmoid colon with resultant partial or complete obstruction
Incidence increases with age.
- Predominant age: >70 years
50% of geriatric ward patients have fecal impaction (1).
Etiology and Pathophysiology
- Age-related degenerative changes of the enteric nervous system and colonic smooth muscle myopathy lead to colonic hypomotility.
- Age-related anatomic changes of the lower GI tract contribute to delayed gut transit time and decreased stool water content.
- Increased rectal compliance and abnormal rectal sensation result in a dilated rectosigmoid colon that accommodates fecal material which is not pliable enough to pass through the anal canal.
- Impacted stool may exist as a single mass (stercolith) or as a composite of small, rounded fecal particles (scybalum). Fecaloma (fecalith) is an extreme form, which presents as a hardened, often calcified, stool mass.
- Poor diet
- Inadequate fiber, water, and caloric intake all contribute to impaction.
- Medication side effect (3)
- Stimulant laxatives
- Opiate analgesics
- Calcium channel blockers
- Aluminum (sucralfate, antacids)
- Neurogenic disorders
- Hirschsprung disease
- Chagas disease
- Autonomic neuropathy
- Multiple sclerosis
- Spinal cord injury
- Cauda equina
- Parkinson disease
- Alzheimer disease
- Metabolic disease
- Diabetes mellitus
- Electrolyte disturbances
- Anatomic abnormalities
- Anorectal stenosis
- Painful rectal conditions inhibiting voluntary defecation (anal fissure, hemorrhoids, fistulas)
- Psychological comorbidities
- Anorexia nervosa
- Pelvic floor dysfunction or dyssynergia
- Irritable bowel syndrome, constipation predominant. Fecal impaction of the cecum may be seen in cystic fibrosis.
In the absence of known syndrome (e.g., Hirschsprung disease), there is no known genetic link.
- Prior history of fecal impaction
- Psychogenic illness
- Immobility, inactivity
- Chronic renal failure
- Urinary incontinence
- Cognitive decline, disability
- Heavy metal ingestion or exposure
- Poor toileting habits
- Excessive seed consumption (common in Middle Eastern cultures), leading to rectal seed bezoars
- Medication (opioids)
Habitual neglect of urge to defecate may promote impaction.
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