From the Guidelines
A CT scan of the abdomen and pelvis without contrast is the preferred imaging method for diagnosing kidney stones. This approach is recommended because virtually all renal calculi are radiopaque on CT, allowing for accurate detection of even small stones at CT without the use of IV contrast 1. The non-contrast CT provides excellent visualization of stones, showing their exact size, location, and any associated blockage or swelling of the urinary tract.
Key Benefits of Non-Contrast CT
- High sensitivity (as high as 97%) for detecting urolithiasis 1
- Ability to visualize secondary signs of urolithiasis and complications such as periureteral and perinephric inflammation and ureteral dilatation
- Rapid acquisition with high spatial resolution and ability for multiplanar reformations
- Low-dose noncontrast CT is a viable option, with a pooled sensitivity of 97% and a pooled specificity of 95% for detecting urolithiasis 1
Considerations for Stone Detection
- The sensitivity for stone detection decreases with smaller stone size
- The sensitivity for small stones can be further hampered with increasing dose reduction 1
- Stone location and size can be accurately depicted at noncontrast CT and have also been associated with spontaneous stone passage rates 1
Clinical Implications
- CT allows for accurate assessment of stone size, which is important in planning urologic management
- CT techniques such as use of coronal reformations, viewing on bone window, and use of magnified views can improve accuracy of stone measurements 1
- Non-contrast CT has been shown to yield equivalent stone measurements compared with standard-dose CT 1
From the Research
CT Abdomen Pelvis for Kidney Stones without Contrast
- The use of non-contrast CT scans for diagnosing kidney stones is a common practice, especially in patients with limited renal function or an allergy to iodinated contrast 2.
- Non-contrast CT scans can be challenging to evaluate, but they can still provide important information about vascular structures and other abnormalities 2.
- Dual-energy CT is a promising imaging technique that can help characterize stone disease and direct therapy 3.
- Ultrasonography is also a viable alternative to CT scans for initial investigation of suspected nephrolithiasis, with lower cumulative radiation exposure and no significant differences in high-risk diagnoses or complications 4, 5.
- A study comparing non-enhanced helical CT with oral contrast-enhanced CT found a 79% simple agreement between the two methods in diagnosing various causes of acute abdominal pain, suggesting that non-contrast CT can be considered in adult ED patients presenting with acute abdominal pain 6.