From the Guidelines
CT scans for kidney stones are typically performed without intravenous contrast. Non-contrast CT is the preferred imaging method for detecting kidney stones because the stones are naturally dense and appear bright on CT images without needing contrast enhancement, as reported in the study by 1. Using contrast can actually obscure small stones, making them harder to detect. The sensitivity for stone detection with non-contrast CT is as high as 97%, making it the reference standard for the evaluation of urolithiasis 1.
Key Points to Consider
- Non-contrast CT allows for rapid acquisition with high spatial resolution and ability for multiplanar reformations, which is beneficial for detecting kidney stones 1.
- Secondary signs of urolithiasis and complications such as periureteral and perinephric inflammation and ureteral dilatation can also be visualized with non-contrast CT 1.
- Low-dose non-contrast CT has been shown to have a pooled sensitivity of 97% and a pooled specificity of 95% for detecting urolithiasis, making it a suitable alternative to standard-dose CT 1.
- The use of coronal reformations, viewing on bone window, and use of magnified views can improve the accuracy of stone measurements on non-contrast CT 1.
Special Considerations
However, in certain situations, such as when evaluating for complications like obstruction, infection, or when there's concern for other pathology beyond simple stone disease, a CT with contrast might be ordered, as discussed in the study by 1. The radiation dose for a non-contrast CT is also lower than for contrast studies, which is beneficial since patients with kidney stones often require multiple scans over time. Additionally, avoiding contrast eliminates the risk of contrast-induced nephropathy, which is particularly important in patients who may already have compromised kidney function due to stone disease.
From the Research
Computed Tomography (CT) Scan for Nephrolithiasis
- A CT scan of the pelvis for nephrolithiasis (kidney stones) is typically performed without intravenous contrast, as stated in the study 2.
- Noncontrast CT of the abdomen and pelvis consistently provides the most accurate diagnosis of kidney stones, but also exposes patients to ionizing radiation 2.
- The use of non-contrast CT is also supported by another study 3, which mentions that CT scans of the abdomen and pelvis are performed in a select subset of patients, including those with suspected renal calculus.
Advantages of Non-Contrast CT
- Non-contrast CT has several advantages, including the ability to accurately diagnose kidney stones without the need for intravenous contrast 2.
- It also has a higher sensitivity and specificity compared to ultrasonography, especially for smaller stones 4.
- Additionally, non-contrast CT can provide detailed images of the renal collecting system, which can be useful for preoperative planning 5.
Alternative Imaging Modalities
- Ultrasonography is an alternative imaging modality that can be used to diagnose kidney stones, but it has a lower sensitivity and specificity compared to non-contrast CT 2, 4.
- MRI is another alternative, but it is costly and currently has limitations in visualizing stones 2.
- Plain abdominal film of kidney, ureter, and bladder (KUB) can be used to evaluate for interval stone growth, but it is less useful in the setting of acute stones 2.