When should contrast be added to a computed tomography (CT) scan of the abdomen and pelvis?

When to Add Contrast to CT Abdomen and Pelvis

IV contrast should be added to CT abdomen and pelvis examinations in most clinical scenarios as it significantly improves diagnostic accuracy by enhancing soft tissue characterization, vascular structures, and detection of pathology. 1

General Principles for Contrast Use

• Standard Protocol: The American College of Radiology recommends a single-phase examination with IV contrast administered in the portal venous phase, typically acquired 70 seconds after contrast administration 1
• Contrast Volume: 100-150 mL of non-ionic iodinated contrast media (e.g., iohexol, ioversol) is recommended for optimal image quality 1
• Oral Contrast: Generally not required for routine venous phase imaging unless specific bowel delineation is needed 1

Clinical Scenarios Where IV Contrast is Essential

1. Oncologic Evaluation

• Cervical Cancer: Contrast-enhanced CT significantly improves detection of nodal disease with pooled sensitivity of 51% and specificity of 87% 2
• Gastric Cancer: IV contrast is necessary to assess for nodular wall thickening and soft tissue attenuation of wall thickening 2

2. Inflammatory/Infectious Conditions

• Acute Pyelonephritis: Contrast-enhanced CT has superior detection rate (84.4%) compared to ultrasound (40%) for complicated pyelonephritis 2
• Epigastric Pain: IV contrast significantly improves conspicuity of findings such as interrupted mucosal enhancement and bowel wall hyperenhancement 2

3. Trauma Assessment

• Blunt Trauma: Contrast-enhanced CT has greater sensitivity for detecting visceral organ and vascular injury compared to non-contrast CT 2
• Active Hemorrhage: IV contrast is essential to detect active bleeding, which appears as extravasated contrast material with higher attenuation (85-370 HU) compared to clotted blood (40-70 HU) 3

4. Vascular Assessment

• GI Bleeding: CTA with IV contrast can detect bleeding at rates as low as 0.5 mL/min 2

When to Avoid IV Contrast

1. Renal Failure:

   • For patients with eGFR < 30 mL/min/1.73m², consider non-contrast CT, alternative imaging modalities, or nephrology consultation 1
   • In patients with AKI, unenhanced CT is preferred for initial evaluation 2

2. Severe Contrast Allergy: History of severe reactions to iodinated contrast media 4

3. Specific Clinical Scenarios:

   • Urolithiasis: Non-contrast CT is the gold standard for detecting renal calculi 2
   • PET-CT scans: Often performed without IV contrast 5

Special Considerations

• Renal Impairment: In patients with impaired renal function, the half-life of iodinated contrast increases (23 hours vs. normal 2.1 hours) 4
• Low-Volume Protocols: For patients with renal insufficiency who still require contrast, high-pitch techniques with very low volumes (30 mL) of contrast media may be feasible 6
• Virtual Contrast Enhancement: Emerging technology may allow synthesis of contrast-enhanced images from non-contrast scans using artificial intelligence 7

Common Pitfalls to Avoid

1. Inappropriate Timing: Scanning too early may result in suboptimal venous enhancement, while excessive delay reduces vessel opacification 1
2. Unnecessary Multiphase Imaging: The addition of non-contrast CT images would not appreciably add to the contrast-enhanced CT evaluation in most cases 2
3. Overlooking Contraindications: Always check for history of severe contrast reactions 1
4. Delaying Diagnosis: For suspected acute abdominal processes in critically ill patients, some studies suggest non-contrast CT may be sufficient (92.5% accuracy) when contrast administration would delay diagnosis 8

By following these guidelines, clinicians can optimize the diagnostic value of CT abdomen and pelvis examinations while minimizing risks to patients.