Is a non-contrast computed tomography (CT) scan or a contrast-enhanced CT scan usually used for diagnosing nephrolithiasis?

Non-Contrast CT is the Standard Imaging Method for Nephrolithiasis

Non-contrast CT (NCCT) is the reference standard for diagnosing nephrolithiasis (kidney stones) with a sensitivity as high as 97% and specificity of 95%. 1, 2

Why Non-Contrast CT is Preferred

• NCCT allows for rapid acquisition with high spatial resolution and ability for multiplanar reformations, making it the gold standard for kidney stone detection 2, 1
• Virtually all renal calculi are radiopaque on CT, allowing for accurate detection of even small stones without the need for IV contrast 2
• NCCT provides precise measurement of stone size and clear depiction of stone location, which are critical factors in determining management approach 1
• Secondary signs of urolithiasis and complications such as periureteral inflammation, perinephric inflammation, and ureteral dilatation can be visualized with NCCT 2, 1
• Low-dose CT protocols (<3 mSv) maintain excellent diagnostic performance while reducing radiation exposure, with pooled sensitivity of 97% and specificity of 95% 1

Why Contrast-Enhanced CT is Not Recommended

• CT with IV contrast is usually not appropriate as a first-line test for kidney stones as the enhancing renal parenchyma may obscure stones within the collecting system 2
• Contrast administration can affect collecting system content density, making it more difficult to distinguish between pyonephrosis and hydronephrosis 2
• There is limited evidence to support the use of CT abdomen with IV contrast for initial imaging of patients with suspected nephrolithiasis 2
• CT abdomen and pelvis without and with IV contrast offers no additional benefit over non-contrast CT alone for kidney stone evaluation 1

Special Considerations

• If a contrast-enhanced CT has already been performed for another reason, it can still detect larger stones (≥6 mm) with approximately 98% accuracy 2
• For patients with recurrent stone disease, limiting the CT scan to the area of interest or using ultra-low-dose protocols can help reduce cumulative radiation exposure 1
• In pregnant patients, ultrasonography is the imaging tool of choice due to radiation concerns 1
• CT abdomen and pelvis without IV contrast is particularly useful when obstructive urolithiasis is the primary concern 2

Optimizing Stone Detection

• Stone detection accuracy can be improved with:
  • Use of coronal reformations 1
  • Viewing on bone window settings 1
  • Use of magnified views 1
  • Thin (1-1.5 mm) axial slice images rather than thick (5 mm) coronal maximum intensity projection images 2
• Even with optimal technique, CT may underreport the total number of renal calculi, particularly missing some small stones or failing to distinguish those lying in close proximity 3

Alternative Imaging Approaches

• Ultrasound may be considered as an initial imaging approach in certain scenarios to reduce radiation exposure, though it has lower sensitivity (24%-57%) compared to CT 2, 4
• When ultrasound is used first, the absence of hydronephrosis makes the presence of a larger ureteral stone (>5 mm) less likely 2
• For patients with negative history of urolithiasis and negative urinalysis, contrast-enhanced CT may be more appropriate as these patients have higher likelihood of alternative diagnoses 5

In conclusion, non-contrast CT remains the imaging modality of choice for suspected nephrolithiasis due to its superior diagnostic performance, ability to accurately measure stone size and location, and utility in treatment planning.