Fecal impaction may be defined as a large compacted mass of feces (fecaloma) that becomes stuck in the colon or rectum and cannot be evacuated by the patient. Fecal impaction is common and causes significant morbidity. Although it can occur at all ages, some groups of patients are more susceptible, such as children and institutionalized elderly persons. Others at particular risk include the physically and mentally incapacitated, persons who are bedridden or dependent on narcotics, and those who have a long history of laxative use.
Several anatomic and physiologic factors contribute to symptoms of chronic constipation and fecal impaction. The sensory function of the rectum and anus may be decreased with age or by neurologic disorders resulting in a higher threshold for sensing rectal distension and urgency. In addition, constipation and slow colonic motility produce harder, more compact stools, causing less rectal distension and eventually leading to restriction in their passage through the relatively fixed diameter of the anus. If this cycle perpetuates, formed stool becomes impacted and overflow may occur, leading to passive, intermittent soiling.
The most common factor predisposing to fecal impaction is constipation, and thus the underlying causes and risk factors are the same ( Boxes 21-1 and 21-2 ). Numerous medications are associated with constipation ( Box 21-3 ). In children, the most frequent cause of fecal impaction is the development of a withholding behavior that may occur after a painful or frightening experience with evacuation at one time, which then perpetuates a cycle of fear of defecation and further stool retention.
Megarectum (e.g., Hirschsprung and Chagas disease)
Benign colonic stricture
Irritable bowel syndrome
Chronic renal failure
Spinal cord injury
Low intake of dietary fiber
Chronic laxative abuse
Decreased colonic motility
Inadequate toilet facilities
Painful anorectal problems
Postoperative (anorectal surgery, orthopedics)
Calcium channel blockers
Nonsteroidal antiinflammatory drugs
Fecal impaction can present with different signs and symptoms, such as constipation, rectal discomfort, lower abdominal pain, rectal fullness, tenesmus, or, in some cases, fecal incontinence or seepage. The most worrisome symptoms are mainly related to secondary complications that occur especially in patients older than 80 years, in those with heart and neurologic disease, and in persons for whom treatment is delayed.
The most common complication of fecal impaction is passive fecal incontinence, also known as overflow incontinence, resulting from a ball-valve effect of the impacted fecal bolus. Loose stool leaks around the immobile fecal mass, resulting in paradoxical diarrhea, and exacerbating the concomitant incontinence that is often present. In fact, fecal impaction is the most common cause of fecal incontinence in nursing homes. Impaction can also affect the urinary tract, causing urinary frequency, urinary overflow incontinence, and even urethral obstruction or ureteral hydronephrosis when the impaction is a large mass.
Fecal impaction is responsible for approximately 3% of all colonic obstructions, especially in patients with spinal cord injuries. Colonic obstructions present with dilatation of the colon proximal to the site of impaction, constipation, nausea, vomiting, and abdominal distension. Unresolved fecal impaction can produce a stercoral perforation of the bowel wall as a result of pressure necrosis from the fecal mass. The most common sites are the antimesenteric border of the sigmoid and rectosigmoid. The clinical presentation is usually an acute abdomen associated with fever, vomiting, severe pain, abdominal tenderness, and an increased leukocyte count. A stercoral perforation of the bowel wall is an uncommon but life-threatening complication for older patients and those whose general condition is poor.
A rectal examination is the most important tool for the diagnosis of fecal impaction. It typically shows hard stool in the rectum, although the absence of palpable stool does not rule out a fecal impaction because the stool can be impacted anywhere in the colon or may have been cleared by prior enemas or suppositories. A plain abdominal radiograph in the supine and upright positions can identify more proximal fecal masses and signs of obstruction. These radiographs will typically reveal involvement of the rectosigmoid in as many as 70% of cases ( Fig. 21-1 ). Small bowel dilatation occurs in extreme cases of impaction as a result of an incompetent ileocecal valve. A radiograph can be the first diagnostic tool in children, patients with psychological problems, and in victims of sexual abuse who refuse to undergo a digital rectal examination.