Yes, CT of the abdomen and pelvis will show renal stones with excellent accuracy.
Noncontrast CT abdomen and pelvis is the reference standard for detecting renal stones, with a sensitivity as high as 97% and is the most appropriate imaging modality for this purpose 1. Virtually all renal calculi are radiopaque on CT, allowing accurate detection of even small stones without the need for intravenous contrast 1.
Key Performance Characteristics
For noncontrast CT:
- Sensitivity: 97% overall 1
- Detects stones of all sizes, though sensitivity decreases with smaller stones
- Provides accurate stone size and location measurements
- Shows secondary signs of obstruction (hydronephrosis, perinephric inflammation, ureteral dilation)
- Low-dose protocols maintain 97% sensitivity while reducing radiation exposure 1
Important Considerations Based on CT Protocol
Noncontrast CT (Preferred)
This is the optimal protocol for stone detection. All stones appear radiopaque without contrast obscuring them 1.
Contrast-Enhanced CT (Suboptimal but Still Useful)
If a patient has already undergone CT with IV contrast:
- Overall sensitivity drops to 81% for all stones (≥1 mm) 1
- Sensitivity improves to 95% for stones ≥3 mm 1
- Detectability of stones ≥6 mm is approximately 98% 1
- The enhancing renal parenchyma during the nephrographic phase can obscure smaller stones in the collecting system 1
Clinical Pitfalls
Important limitation: While CT has 97% sensitivity, endoscopic studies show CT actually underreports the total number of stones present (detecting an average of 5.9 stones per kidney versus 9.2 found at endoscopy) 2. However, the total stone burden (sum of stone diameters) remains accurate 2. This means CT may miss some very small stones or fail to distinguish stones lying close together, but it accurately captures clinically significant stone disease.
Rare exception: Stones composed of certain materials like surgical adhesives (n-butyl α-cyanoacrylate) may not be detectable on CT 3, though this is exceedingly uncommon in clinical practice.
Bottom Line Algorithm
- For suspected renal stones: Order noncontrast CT abdomen and pelvis
- If contrast CT already performed: Stones ≥3 mm will be detected with 95% sensitivity; stones ≥6 mm with 98% sensitivity
- Stone size matters: Larger stones (≥3 mm) are detected with near-perfect accuracy regardless of contrast use
- Clinical significance: The stones most likely to require intervention (larger stones) are reliably detected even on contrast-enhanced studies