What type of ultrasound is recommended for suspected kidney stones?

Non-Contrast CT is the Recommended Ultrasound for Kidney Stones

Non-contrast CT of the abdomen and pelvis is the gold standard imaging modality recommended for the diagnosis of kidney stones, with a sensitivity of up to 97% for urolithiasis detection. 1

Primary Imaging Recommendations

Non-Contrast CT

• Provides detailed information about:
  • Stone size and location
  • Secondary signs of obstruction
  • Periureteral and perinephric inflammation
  • Alternative diagnoses that may mimic urolithiasis
• Allows for accurate detection of small stones and assessment of stone size, which is critical for management planning 1
• Has become the gold standard for evaluation of urinary stones 2

Alternative Imaging Options

Ultrasound (When Radiation Exposure is a Concern)

• Reasonable alternative when radiation exposure is a concern or CT is unavailable
• Sensitivity of up to 100% and specificity of up to 90% for diagnosing ureteral obstruction
• Improved sensitivity for small renal stones (up to 99% for stones <5mm) when combined with color Doppler and twinkling artifact assessment 1
• Advantages:
  • No radiation exposure
  • Lower cost
  • Widely available 3
• Limitations:
  • Decreased sensitivity (45%) and specificity (88%) for renal calculi compared to CT 3
  • Inaccuracy in measuring stone size
  • Observer dependency
  • Reduced sensitivity for stones <3mm 3

Special Clinical Scenarios

Pregnant Patients

• Ultrasound color Doppler of kidneys, bladder, and retroperitoneum is recommended as the initial imaging modality 4
• MRI without IV contrast may be appropriate as an alternative 4

Pediatric Patients

• For suspected urolithiasis in children with painful hematuria:
  • Ultrasound of the kidneys and bladder is often the first-line imaging test
  • CT may be particularly useful when ultrasound is negative but clinical suspicion remains high 4

Improving Accuracy of Ultrasound for Stone Detection

When using ultrasound for kidney stone evaluation, accuracy can be improved by:

• Adjusting gain and depth settings
• Using alternative modes such as flash angle imaging, harmonic mode, and S mode
• Using shadow for size measurement
• Employing automated computerized stone-sizing programs to reduce user variability 3

Follow-up Imaging Recommendations

• For follow-up of known renal stones, conventional radiography and ultrasound are recommended rather than repeated CT scans 2
• This approach reduces radiation exposure while maintaining adequate monitoring capability

Common Pitfalls to Avoid

• Relying solely on urinalysis to rule out urolithiasis (10-15% of confirmed cases may have negative urinalysis)
• Overlooking non-urological causes of flank pain
• Failing to consider contrast-enhanced imaging when non-contrast studies are inconclusive 1

In summary, while non-contrast CT is the gold standard for kidney stone diagnosis, the choice of imaging modality should consider radiation exposure, with ultrasound being a reasonable alternative in specific scenarios such as pregnancy, pediatric cases, or for follow-up imaging of known stones.