For a patient with chronic abdominal bloating, should I order a CT scan with or without contrast?

CT Imaging for Chronic Abdominal Bloating

For chronic abdominal bloating without alarm features suggesting acute pathology, CT imaging is generally not indicated as a first-line diagnostic test, and if imaging is pursued, CT abdomen/pelvis with IV contrast (without oral contrast) is the appropriate choice.

Understanding the Clinical Context

Chronic abdominal bloating is primarily a functional disorder involving altered gut perception, impaired reflex control of intestinal contents, and viscerosomatic reflex abnormalities rather than structural pathology detectable on CT 1. The pathophysiology involves subjective sensation, objective distention, volume of intra-abdominal contents, and abdominal wall muscular activity—mechanisms that are typically subtle and undetectable by conventional imaging methods 1.

When CT Is Actually Indicated

CT should be reserved for patients with chronic bloating who have:

• Red flag symptoms suggesting structural disease: unintentional weight loss, gastrointestinal bleeding, progressive dysphagia, persistent vomiting, or palpable abdominal mass
• Suspected complications such as obstruction, perforation, or inflammatory conditions
• Failed empiric treatment with persistent symptoms requiring exclusion of organic pathology

Choosing the Appropriate CT Protocol

CT with IV Contrast (Without Oral Contrast)

When CT is indicated, IV contrast without oral contrast is the preferred protocol for the following reasons:

• IV contrast is essential for detecting mucosal hyperenhancement, submucosal edema, and abnormal bowel wall enhancement patterns that indicate inflammatory conditions like Crohn's disease 2, 3
• Positive oral contrast obscures subtle mucosal enhancement patterns and can impede assessment of intraluminal pathology 2
• Neutral oral contrast or water provides adequate intrinsic contrast from nonopacified fluid in the bowel without obscuring mucosal detail 2
• IV contrast improves detection of complications including bowel ischemia, perforation, and inflammatory processes with sensitivity of 75-90% for conditions like Crohn's disease 4, 3

Avoid Non-Contrast CT

Non-contrast CT has markedly poorer performance and should not be used for evaluating suspected gastrointestinal pathology 4, 3. While it may detect gross findings like extraluminal gas or large masses, it cannot assess:

• Mucosal enhancement patterns indicating inflammation
• Bowel wall perfusion suggesting ischemia
• Subtle inflammatory changes in the bowel wall 2, 4

Specific Clinical Scenarios

If Inflammatory Bowel Disease Is Suspected

• CT enterography (with neutral oral contrast and IV contrast) is the optimal protocol with 75-90% sensitivity for detecting Crohn's disease 4, 3
• If CT enterography is unavailable, standard CT abdomen/pelvis with IV contrast alone is acceptable 3
• Standard CT has lower sensitivity than CT enterography but remains useful for detecting complications like abscesses (86-100% sensitivity) and fistulas (68-100% sensitivity, though enteroenteric fistulas have only 20% sensitivity) 4

If Small Bowel Obstruction Is Suspected

• IV contrast is preferable to assess bowel perfusion and detect ischemia 2
• Oral contrast is not needed and can delay diagnosis, increase patient discomfort, and risk aspiration in high-grade obstruction 2
• Non-opacified fluid in dilated bowel provides adequate intrinsic contrast 2
• CT with IV contrast has >90% accuracy for diagnosing small bowel obstruction and determining its cause 2, 5, 6

If Peptic Ulcer Disease or Perforation Is Suspected

• IV contrast with neutral oral contrast (water or dilute barium) is recommended 2
• IV contrast assesses submucosal edema, mucosal hyperenhancement, and focal wall defects 2
• Positive oral contrast can impede assessment of mucosal enhancement and intraluminal bleeding 2

Critical Pitfalls to Avoid

• Do not order CT routinely for uncomplicated chronic bloating, as it is a functional disorder unlikely to show structural abnormalities 1
• Do not use positive oral contrast when inflammatory conditions or mucosal pathology are suspected, as it obscures enhancement patterns 2, 3
• Do not rely on non-contrast CT for evaluating gastrointestinal pathology, as it has poor performance for detecting inflammation and ischemia 4, 3
• Do not assume normal CT excludes disease: CT enterography misses 10-25% of Crohn's disease cases, and standard CT has even lower sensitivity 4
• Do not delay endoscopy when appropriate, as colonoscopy with ileoscopy remains the reference standard for mucosal disease 4

Practical Algorithm

1. Assess for alarm features: If present (weight loss, bleeding, obstruction symptoms), proceed with imaging
2. Choose CT protocol based on suspected pathology:
   • Suspected IBD: CT enterography preferred, or CT with IV contrast alone if unavailable 3
   • Suspected obstruction: CT with IV contrast, no oral contrast 2
   • Suspected perforation/ulcer: CT with IV contrast and neutral oral contrast 2
   • General evaluation: CT with IV contrast alone 7
3. If CT is negative but clinical suspicion remains high, pursue endoscopic evaluation 4