What type of computed tomography (CT) scan of the abdomen (abd) and pelvis should be ordered for a suspected case of constipation in an adult patient with a history of gastrointestinal issues?

CT Imaging for Suspected Constipation

You should not routinely order CT imaging for uncomplicated constipation—plain abdominal radiographs have limited clinical utility and rarely change management, while CT should be reserved only for patients with high-risk features suggesting bowel obstruction or alternative serious pathology. 1

When CT Is NOT Indicated

Simple constipation does not require CT imaging. The evidence strongly demonstrates that imaging—whether plain radiography or CT—has minimal impact on management decisions in straightforward constipation cases. 1

• In a study of 1,142 ED patients with constipation, plain abdominal radiographs failed to meaningfully guide treatment—55% of patients with no/mild stool burden still received constipation treatment, while 42% with moderate-to-large stool burden received no ED treatment at all. 1
• Fecal loading on imaging does not exclude more serious diagnoses, and treatment frequently contradicted radiographic findings. 1
• For chronic constipation, plain films can document fecal impaction extent, but this rarely changes the clinical approach. 2

When CT IS Indicated: High-Risk Features

Order CT abdomen and pelvis WITH IV contrast if the patient has concerning features suggesting bowel obstruction or alternative pathology rather than simple constipation. 3, 4

High-Risk Features Requiring CT:

• Advanced age with complex surgical history 1
• Prior small bowel obstruction 1
• Abdominal malignancy 1
• Vomiting or inability to pass flatus 1
• Acute onset of constipation (suggests colonic obstruction) 2
• Severe abdominal pain disproportionate to constipation 3

Specific CT Protocol When Imaging Is Necessary

CT abdomen and pelvis with IV contrast only (no oral contrast) is the appropriate study. 3, 4, 5

Protocol Rationale:

• IV contrast is essential to detect bowel wall enhancement abnormalities indicating ischemia, evaluate vascular perfusion, and identify complications like strangulation. 3, 5
• Studies show IV contrast administration increases detection of urgent pathology compared to non-contrast CT (p=0.004). 5
• Oral contrast is unnecessary for suspected obstruction—the fluid-filled dilated bowel provides intrinsic contrast, and oral contrast delays diagnosis without improving accuracy. 3, 4, 6
• Modern CT technology with multiplanar reconstructions eliminates the need for oral contrast in most acute abdominal scenarios. 3, 6
• CT with IV contrast alone has 92.5% diagnostic accuracy for acute abdominal processes. 7

CT Diagnostic Capabilities:

• Distinguishes true small bowel obstruction from adynamic ileus with >90% accuracy 4
• Identifies transition points and obstruction causes 4
• Detects life-threatening complications: ischemia, strangulation, closed-loop obstruction, volvulus 4

Alternative Imaging for Specific Scenarios

Plain abdominal radiographs may suffice only to determine the level and cause of acute colonic obstruction (e.g., sigmoid or cecal volvulus) when this specific diagnosis is strongly suspected. 2

Barium enema or colonoscopy can detect causes of colonic obstruction but are not first-line for suspected constipation. 2

Critical Pitfalls to Avoid

• Do not order imaging reflexively for constipation complaints—history and physical examination should exclude serious pathology before considering any imaging. 1
• Do not order non-contrast CT when bowel obstruction or ischemia is a concern—IV contrast is mandatory to assess bowel viability. 5
• Do not delay CT with oral contrast administration in patients with high-grade obstruction—this worsens patient discomfort and delays diagnosis without benefit. 3, 6
• Do not assume normal imaging excludes pathology—15 of 16 patients with small bowel obstruction in one study had identifiable high-risk features on history/exam that should have prompted different diagnostic approaches. 1