Can a pelvis computed tomography (CT) scan without contrast (intravenous contrast media) show access to certain areas of the pelvis in patients with impaired renal function or a history of allergy to contrast agents?

Can Pelvis CT Without Contrast Show Abscess?

Yes, pelvis CT without contrast can detect abscesses, but it has significant limitations compared to contrast-enhanced CT and should only be used when IV contrast is contraindicated. Non-contrast CT can identify fluid collections and define their extent, but contrast-enhanced CT is superior for characterizing these collections, distinguishing abscesses from other fluid types, and detecting complications 1.

Diagnostic Capabilities of Non-Contrast Pelvic CT

What Non-Contrast CT Can Show

• Suspected hemorrhage or fluid collections: Non-contrast CT pelvis is helpful for detecting peritransplant fluid collections and suspected hemorrhage, allowing visualization of the extent of these collections 1
• Basic anatomic assessment: The study can define the extent and location of fluid collections in the pelvis, though it cannot reliably characterize their nature 1
• Limited vascular evaluation: While challenging, some vascular pathology can be inferred on non-contrast CT through indirect signs and associated findings 2

Critical Limitations Without Contrast

• Cannot characterize fluid collections: Non-contrast CT cannot reliably distinguish between different types of perinephric collections such as abscesses, seromas, lymphoceles, or urinomas 1
• Misses enhancement patterns: The thick enhancing walls characteristic of abscesses and tubo-ovarian abscesses cannot be visualized without IV contrast 3
• Lower sensitivity for urgent pathology: Studies demonstrate that IV contrast administration significantly improves detection of urgent findings (89% sensitivity with contrast vs 70% without) 3, 4

When Contrast-Enhanced CT is Strongly Preferred

Clinical Scenarios Requiring Contrast

• Severe pelvic inflammatory disease: The American College of Radiology recommends contrast-enhanced CT abdomen and pelvis for detecting complications and guiding treatment decisions in severe PID 3
• Suspected abscess or complex infection: Contrast enhancement is essential for identifying the thick enhancing walls of abscesses and distinguishing them from other fluid collections 3
• Nonspecific clinical presentation: When the differential diagnosis is broad or clinical presentation unclear, contrast-enhanced CT demonstrates superior diagnostic performance 3, 4

Evidence Supporting Contrast Use

• Improved urgent pathology detection: Administration of IV contrast for CT abdomen/pelvis is associated with significantly increased detection of urgent findings compared to non-contrast CT (p = 0.004) 4
• Better characterization: A contrast-enhanced CT following an initial non-contrast CT better characterizes both urgent (p = 0.002) and non-urgent findings (p < 0.001) 4
• Avoids repeat imaging: Adherence to ACR appropriateness criteria for IV contrast administration increases detection of urgent pathology and may avoid short-term repeat CT examinations 4

Appropriate Use of Non-Contrast Pelvic CT

Valid Indications

• Absolute contraindications to contrast: Patients with previous anaphylactic reactions to iodinated contrast 1, 5
• Severe renal impairment: When contrast-induced nephropathy risk outweighs diagnostic benefit, though this threshold is not absolute 6, 5
• Specific clinical questions: Evaluation for urinary obstruction, nephrolithiasis, or suspected hemorrhage where contrast may not add significant value 1

Risk-Benefit Considerations

• Renal function assessment: eGFR should be calculated each time creatinine is measured using validated formulas, but there are no absolute serum creatinine thresholds that contraindicate IV contrast 6
• Careful monitoring: Patients with impaired renal function should have careful monitoring after contrast administration rather than automatic exclusion from contrast studies 6
• Alternative modalities: Ultrasound with contrast enhancement (CEUS) provides an excellent safety profile for patients unable to undergo contrast-enhanced CT, including those with end-stage renal disease or contrast allergies 7

Common Pitfalls to Avoid

• Ordering non-contrast CT by default: Failing to use IV contrast when not contraindicated is a common diagnostic error, as the bulk of evidence supporting CT for pelvic pathology refers specifically to contrast-enhanced imaging 3
• Assuming non-contrast is "safer": The radiation exposure is identical, and avoiding contrast may lead to non-diagnostic studies requiring repeat imaging with higher cumulative radiation 4
• Not considering ultrasound first: For many pelvic pathologies, ultrasound should be the initial imaging modality, with CT reserved for when additional information is needed 6

Practical Algorithm

1. First-line imaging: Use ultrasound as initial modality for suspected pelvic abscess or fluid collection 6
2. If ultrasound nondiagnostic or severe disease suspected: Proceed to contrast-enhanced CT pelvis (or abdomen/pelvis if broader evaluation needed) 3
3. Only use non-contrast CT when:
   • True anaphylactic contrast allergy documented 1, 5
   • Severe renal impairment where risk clearly outweighs benefit after careful assessment 6, 5
   • Specific indication where contrast adds no value (e.g., suspected renal stone) 1
4. If non-contrast CT performed and shows fluid collection: Recognize that characterization is limited and additional imaging (contrast-enhanced CT, MRI, or ultrasound with contrast) will likely be needed 1, 3