Fecal Impaction

Fecal impaction is often seen as an acute complication of severe or untreated chronic constipation. When an individual is constipated, stool remains in the large intestine for longer than usual, giving the intestine more time to absorb water from the fecal matter. The excessively dried stool can thereby turn into a hard mass that can become impacted in the final part of the gastrointestinal tract, typically in the sigmoid colon or rectum.  

Risk factors for developing a fecal impaction include eating a low-fiber diet, not drinking enough fluids, and having a sedentary lifestyle. In addition, taking medications, like antidepressants, opioid analgesics, or iron supplements, can worsen constipation by slowing down bowel movements or by making stools harder and more difficult to pass. In some cases, constipation can be a symptom of an underlying medical condition, including irritable bowel syndrome, inflammatory bowel disease, diverticulitis, anorectal malformations, and colorectal cancer. Finally, constipation can result from electrolyte abnormalities (e.g., elevated calcium levels); hypothyroidism; and neurological disorders, like Alzheimer disease, spinal cord injuries, or Parkinson disease. 

Signs and symptoms of fecal impaction include lower abdominal pain, inability to pass bowel movements, and rectal fullness or discomfort. The most common complication of fecal impaction is passive fecal incontinence, also known as overflow diarrhea, which occurs when liquid stool leaks around the fecal impaction. The impaction can also affect the urinary tract, causing increased urinary frequency, urinary overflow incontinence, and even urethral obstruction or hydronephrosis if the fecal mass is very large. With time, fecal impaction can lead to colonic inflammation (i.e., stercoral colitis), or even erosions caused by the impaction of feces (i.e., stercoral ulcers). 

Rarely, fecal impaction can lead to a bowel obstruction, which can present with dilation of the colon proximal to the site of impaction, abdominal distention, nausea, and vomiting. Eventually, if bowel dilation becomes excessive, the intestinal wall can face extreme pressure, which may cause the blood vessels within the walls to collapse. When that happens, perfusion to the intestine can become compromised, leading to perforations of the bowel wall as a result of pressure necrosis from the fecal mass (i.e., stercoral perforations).  

Differential diagnoses involve considering various possible conditions that could be causing symptoms and then ruling out each one through use of history, clinical evaluation, diagnostic tests, and critical thinking. This process helps to narrow down the list of potential diagnoses to determine the most likely cause of the symptoms. 

Differential diagnoses can be broken down into four categories: most likely, less likely, least likely, and can’t miss. Most likely diagnoses are conditions most probable based on symptoms and clinical presentation. Less likely diagnoses are not as probable but should still be considered. On the other hand, least likely diagnoses can be considered if other, more probable conditions are excluded. Finally, can’t miss diagnoses are less common but critical to promptly identify and treat as they can lead to severe consequences.  

Diagnosis of fecal impaction begins with a thorough medical history and physical exam. Physical exam should focus on ruling out signs of stercoral colitis, such as fever, tachycardia, or peritoneal signs, like abdominal guarding, rigidity, and rebound tenderness (i.e., Blumberg sign). A digital rectal exam is the most important tool for the diagnosis of a fecal impaction. The exam is usually conducted while the individual lies on their side with their knees flexed towards their chest. The examiner then inserts a gloved, lubricated finger into the rectum and feels for strictures, rectal tenderness, masses, and presence of stool. With fecal impaction, a digital rectal exam typically reveals a mass of stool in the rectum. The absence of palpable stool in the rectum, however, doesn’t rule out a fecal impaction since the stool can be impacted anywhere in the colon.  

Further diagnostic tests may include blood tests to look for signs of inflammation or bowel ischemia as well as an abdominal X-ray. In cases of bowel obstruction, an X-ray may show dilated bowel loops with air-fluid levels, which means that both fluid and gas are collecting proximal to the point of obstruction. If perforation has occurred, there may be radiographic evidence of free intraperitoneal air that has leaked from the intestines into the abdominal cavity. Finally, a CT scan may be conducted in cases where the diagnosis is unclear or when there are complications, like a bowel obstruction or perforation. Once the fecal impaction has been resolved, additional tests may be needed to identify the underlying cause of impaction. 

Treatment of fecal impaction is aimed at relieving the symptoms and preventing future recurrences. In cases where the mass of the stool is palpable in the rectum, it can be removed manually by gently fragmenting it with the index finger via scissoring motions. In such cases, administering a stool softener or enema can assist in breaking down the stool and stimulating the rectum to evacuate it.  

If the stool is beyond the reach of enemas and the individual shows no signs of bowel obstruction, oral laxatives like polyethylene glycol can be administered in order to help draw water into the intestinal lumen and increase gastrointestinal motility. Alternatively, the fecal mass can be removed via endoscopic disimpaction. Finally, although fecal impaction can be managed conservatively in most cases, individuals with a complete bowel obstruction or evidence of complications may require surgical evaluation.   

Prevention of fecal impaction is typically advised since recurrences are very common. Individuals at high risk for fecal impaction should increase their dietary fiber and water intake, take daily fiber supplements or stool softeners (e.g., docusate sodium), use weekly enemas if no bowel movement occurs, and treat any underlying disorders to avoid future episodes of fecal impaction.