From the Guidelines
No, a CT stonogram typically does not require contrast. A CT stonogram is a specialized CT scan specifically designed to detect kidney stones and is performed without intravenous contrast. This non-contrast technique is preferred because kidney stones are naturally dense and appear bright on CT images without the need for contrast enhancement. Additionally, using contrast might actually obscure small stones by creating similar densities in the urinary tract. Non-contrast CT has become the gold standard for diagnosing urinary tract stones due to its high sensitivity (95-98%) and specificity, as reported in the study by 1.
Key Points
- Non-contrast CT allows for accurate detection of even small stones at CT without the use of IV contrast, with a reported sensitivity as high as 97% 1.
- The use of low-dose noncontrast CT for stone assessment has increased, with a meta-analysis of 7 studies assessing the diagnostic performance of low-dose (<3 mSv) CT for detecting urolithiasis finding a pooled sensitivity of 97% and a pooled specificity of 95% 1.
- Stone location and size can be accurately depicted at noncontrast CT and have also been associated with spontaneous stone passage rates, with more proximal as well as larger stones having a higher need for intervention 1.
- In certain complex cases where additional information about kidney function or anatomy is needed, a separate contrast-enhanced study might be ordered, but this would be in addition to, not instead of, the non-contrast stonogram.
Imaging Considerations
- CT urography (CTU) is an imaging study that is tailored to improve visualization of both the upper and lower urinary tracts, and may involve the use of IV contrast, but is not typically used for initial stone detection 1.
- Other imaging modalities, such as ultrasound and digital tomosynthesis, may also be used to detect kidney stones, but non-contrast CT remains the gold standard due to its high sensitivity and specificity 1.
From the Research
CT Stonogram and Contrast Requirements
- A CT stonogram is a type of computed tomography (CT) scan used to evaluate urinary stones, and it does not necessarily require contrast 2.
- The use of contrast-enhanced CT to detect renal stones has been investigated, and it has been found that the detectability of renal stones is extremely high, especially for stones ≥ 6 mm 3.
- However, the use of contrast media in patients with kidney disease is a topic of discussion, and risk stratification prior to contrast media use in patients with pre-existing renal dysfunction should be based on eGFR-determination 4.
- In general, the risk of iodinated contrast-induced acute kidney injury is minimal in patients with an estimated glomerular filtration rate greater than 30 mL/min/1.73 m2, and preventive strategies such as hydration with 0.9% saline and limiting contrast volume may further reduce acute kidney injury risk in susceptible individuals 5.
Specific Considerations
- For patients with kidney failure, the approach to imaging continues to evolve, and the use of contrast media should be carefully considered 6.
- In patients with advanced renal insufficiency, ensuring euvolemia is crucial, and there is no evidence for any other preventive approach to prevent contrast-associated kidney injury 4.
- The use of iodinated contrast media or group II gadolinium-based contrast agents should not be postponed in chronic kidney disease patients when clinically significant imaging studies are required 5.