What is the best imaging study to evaluate constipation?

Best Imaging Study for Evaluating Constipation

For patients with constipation, a structural evaluation with colonoscopy, computed tomographic colonography, or flexible sigmoidoscopy with barium enema is the most appropriate initial imaging approach when indicated by alarm symptoms, abrupt onset of constipation, or age over 50 years without previous colorectal cancer screening. 1

Initial Assessment Approach

• A thorough digital rectal examination that includes assessment of pelvic floor motion during simulated evacuation should be performed before ordering imaging studies 1
• Laboratory testing should be limited to a complete blood count in the absence of other symptoms and signs 1
• Metabolic tests (glucose, calcium, thyroid-stimulating hormone) are not routinely recommended unless clinical features warrant them 1

Imaging Selection Algorithm

Step 1: Determine if structural evaluation is needed

• Indications for structural imaging:
  • Presence of alarm symptoms (blood in stools, anemia, weight loss) 1
  • Abrupt onset of constipation 1
  • Age over 50 years without previous colorectal cancer screening 1

Step 2: Select appropriate structural imaging based on clinical context

• First-line options:
  • Colonoscopy (preferred for direct visualization and biopsy capability) 1
  • CT colonography (excellent alternative when colonoscopy is contraindicated) 1
  • Flexible sigmoidoscopy with barium enema (effective combination) 1

Step 3: Consider functional imaging for refractory cases

• For patients with persistent symptoms despite initial treatment:
  • Colonic transit studies (using radiopaque markers) to assess for slow transit constipation 1
  • Defecography (fluoroscopic or MR) for suspected defecatory disorders 1, 2

Special Considerations for Specific Scenarios

For Suspected Defecatory Dysfunction

• Fluoroscopic cystocolpoproctography (CCP) is one of the initial tests of choice 1
  • Reveals clinically occult sigmoidoceles, enteroceles, and rectoanal intussusceptions 1
  • Detection of these diagnoses on defecography has been shown to alter clinical assessment in a significant percentage of patients 1

For Suspected Pelvic Floor Abnormalities

• MR defecography provides high soft-tissue contrast resolution for direct visualization of pelvic organs and floor muscles 1, 2
  • Particularly useful for evaluating complex pelvic floor disorders 1

For Acute Constipation

• Plain abdominal radiographs may be sufficient to determine the level and cause of obstruction, such as sigmoid or cecal volvulus 3
• However, plain abdominal radiography appears to have low value in routine evaluation of constipation 4
  • Treatment decisions often contradict radiographic findings 4
  • Fecal loading on radiography does not preclude more serious diagnoses 4

Common Pitfalls to Avoid

• Relying solely on plain abdominal radiographs for diagnosis of constipation 4

  • Limited utility in routine evaluation despite common use 4
  • Poor correlation between radiographic findings and clinical management 4

• Failing to consider functional disorders when structural imaging is normal 1

  • Up to 75% of patients may have dyssynergic defecation detected on specialized testing 5

• Overlooking the need for structural evaluation in high-risk patients 1

  • Missing colorectal cancer or other structural abnormalities that could cause constipation 1

• Ordering excessive testing without clinical indication 1

  • Most cases of constipation can be managed without extensive imaging 1