What is the recommended CT (Computed Tomography) imaging protocol for a patient presenting with flank pain?

CT Imaging Protocol for Flank Pain

Non-contrast CT of the abdomen and pelvis is the gold standard imaging protocol for patients presenting with flank pain, with a sensitivity of up to 97% for detecting urolithiasis. 1, 2

Primary Imaging Recommendation

Non-contrast CT Abdomen and Pelvis

• Considered the reference standard for evaluation of urolithiasis 1
• Virtually all renal calculi are radiopaque on CT, allowing for accurate detection of even small stones 1
• Provides high spatial resolution with ability for multiplanar reformations 1
• Can detect secondary signs of urolithiasis and complications (periureteral inflammation, perinephric inflammation, ureteral dilatation) 1
• No need for contrast preparation, making it faster and safer than contrast studies 1
• Sensitivity as high as 97% for detecting urinary stones 1, 3
• Can identify alternative diagnoses in approximately 30% of patients with flank pain 3

Alternative Imaging Options

Ultrasound (Kidneys and Bladder)

• Appropriate alternative when:
  • Patient is pregnant
  • Radiation exposure is a concern
  • CT is contraindicated or unavailable 1, 2
• Sensitivity up to 100% and specificity up to 90% for diagnosing ureteral obstruction 1
• Less sensitive for direct stone visualization, particularly for ureteral stones (only 38% sensitivity) 2
• Addition of color Doppler and assessment of twinkling artifact improves sensitivity for small renal stones (up to 99% for stones <5mm) 1, 2
• May miss stones within the first 2 hours of presentation as secondary signs of obstruction may not have developed 1

CT with IV Contrast

• Not recommended as first-line for suspected urolithiasis 1
• Consider when:
  • Initial non-contrast CT is negative but symptoms persist
  • Alternative diagnoses are strongly suspected
• Contrast may obscure small stones within the renal collecting system 1
• Can better delineate "soft tissue rim" sign to differentiate ureteral stones from phleboliths 1
• Detectability of renal stones ≥6 mm on contrast-enhanced CT remains high (approximately 98%) 1

Clinical Considerations

When to Use Non-contrast CT

• First-line imaging for most adult patients with acute flank pain 1, 2
• When urolithiasis is the primary diagnostic consideration 1
• When rapid diagnosis is needed 3

When to Consider Alternative Imaging

• Pregnant patients: Ultrasound is usually appropriate as initial imaging 1
• Children: Ultrasound may be preferred to minimize radiation exposure 2
• Patients with known current stone disease with recurrent symptoms: Non-contrast CT remains the standard 1

Pitfalls and Caveats

• Follow-up contrast-enhanced CT after initial non-enhanced CT rarely changes management (only in 1.9% of cases) 4
• Low-dose CT protocols can be considered to reduce radiation exposure without significantly compromising diagnostic accuracy 1
• Hydronephrosis on ultrasound does not accurately predict the presence or absence of a ureteral stone in up to 25% of patients 1
• The lack of hydronephrosis on ultrasound makes the presence of a larger ureteral stone (>5 mm) less likely 1

By following these evidence-based recommendations, clinicians can efficiently diagnose urolithiasis and other causes of flank pain while minimizing unnecessary radiation exposure and contrast administration.