What imaging studies are recommended for a patient with constipation?

Imaging Studies for Constipation

For patients with constipation, imaging studies are generally not routinely necessary unless alarm features are present or initial management fails, with colonoscopy being indicated primarily for patients over 50 years or those with alarm symptoms. 1

Initial Assessment Before Imaging

• A thorough digital rectal examination should be performed, including:

  • Assessment of pelvic floor motion during simulated evacuation
  • Evaluation of resting sphincter tone and contraction
  • Examination of the puborectalis muscle
  • Request for the patient to "expel the examiner's finger" 1

• Basic laboratory testing:

  • Complete blood count (strong recommendation) 1
  • Metabolic tests (glucose, calcium, thyroid-stimulating hormone) are NOT routinely recommended unless clinically indicated 1

When to Consider Imaging

Alarm Features Requiring Imaging:

• Age > 50 years without recent colorectal cancer screening
• Blood in stools/rectal bleeding
• Anemia
• Weight loss
• Abdominal mass
• Family history of colorectal cancer
• Abrupt onset of constipation
• Fever 1, 2

Recommended Imaging Studies

1. Structural Evaluation of the Colon

• Colonoscopy:
  • Indicated for patients with alarm features
  • Necessary for patients >50 years without recent screening
  • NOT recommended for patients without alarm features 1, 2

2. For Suspected Defecatory Disorders

• Anorectal manometry and balloon expulsion test should be performed first 1
• Fluoroscopic defecography (cystocolpoproctography) is recommended when:
  • Discordant findings exist between manometry and balloon expulsion test
  • Need to identify structural abnormalities (rectocele, enterocele, sigmoidocele, rectal intussusception) 1

3. For Suspected Slow Transit Constipation

• Colonic transit study should be performed if:
  • Anorectal tests do not show a defecatory disorder
  • Symptoms persist despite treatment of a defecatory disorder 1

4. For Acute Constipation or Suspected Obstruction

• Plain abdominal radiograph may be useful to:
  • Determine level and cause of obstruction
  • Exclude bowel obstruction
  • Assess extent of fecal loading 3

What NOT to Do

• Do not routinely order plain abdominal radiographs for chronic constipation as they have low diagnostic value 4
• Avoid CT scans for functional assessment of defecatory dysfunction 1
• Do not rely solely on radiographic evidence of stool burden for diagnosis, as patients with significant stool burden on imaging may have alternative diagnoses 4

Special Considerations

• In patients with defecatory dysfunction, imaging helps identify clinically occult conditions such as sigmoidoceles, enteroceles, and rectoanal intussusceptions 1
• For suspected ischemic colitis (a potential complication), CT with IV contrast is the first-line imaging modality 5
• Abdominal radiographs may indicate diagnostic uncertainty; the presence of stool on radiographs does not rule out alternative diagnoses 6

Clinical Decision Algorithm

1. Perform digital rectal examination and basic laboratory tests
2. If alarm features present → Proceed to colonoscopy
3. If no alarm features → Trial of conservative management
4. If symptoms persist → Evaluate for defecatory disorders with anorectal testing
5. If anorectal testing is normal or symptoms persist despite treatment → Assess colonic transit
6. For suspected structural abnormalities → Consider defecography

Remember that imaging studies should complement, not replace, thorough clinical assessment in patients with constipation.