From the Guidelines
For diagnosing renal stones, contrast-enhanced computed tomography (CT) is not necessary, and non-contrast CT is the recommended first-line approach. A non-contrast CT scan is highly sensitive and specific for detecting kidney stones, with a reported sensitivity as high as 97% 1. This technique can accurately identify the size, location, and number of stones present, and also allows for the assessment of stone density and composition, which can guide treatment decisions.
The advantages of non-contrast CT include:
- Faster scan time
- No risk of contrast-related allergic reactions
- Avoidance of potential kidney damage from contrast agents
- Ability to detect both radiopaque and radiolucent stones
- Low-dose noncontrast CT has been shown to yield equivalent stone measurements compared with standard-dose CT, with a pooled sensitivity of 97% and a pooled specificity of 95% 1
In rare cases where there's suspicion of a complicated stone or associated infection, a contrast-enhanced CT may be considered as a secondary study. However, for routine renal stone evaluation, non-contrast CT remains the gold standard, as it allows for rapid acquisition with high spatial resolution and ability for multiplanar reformations, and can also visualize secondary signs of urolithiasis and complications such as periureteral and perinephric inflammation and ureteral dilatation 1.
Patients should be instructed to hold still during the scan and may need to hold their breath briefly. The entire procedure typically takes 10-15 minutes. No special preparation is required, but patients should inform the technologist if there's any chance of pregnancy. 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.
From the Research
Diagnosis of Renal Stones
- Non-contrast computed tomography (CT) is becoming the standard imaging modality in urinary stone disease 2
- Non-contrast spiral CT scan is a reliable and rapid diagnostic modality for the detection of urinary stones, providing a morphological study equivalent to that of intravenous urography (IVU) 3
- Non-contrast enhanced CT of kidneys, ureters and bladder (CT KUB) has extremely high sensitivity and specificity in the diagnosis of stones 4
Comparison with Other Imaging Modalities
- Ultrasonography has a lower sensitivity and specificity than CT, but does not require use of radiation 5
- MRI provides the possibility of 3D imaging without exposure to radiation, but it is costly and currently stones are difficult to visualize 5
- Kidney, ureter, bladder (KUB) plain film radiography is most helpful in evaluating for interval stone growth in patients with known stone disease, and is less useful in the setting of acute stones 5
Use of Contrast-Enhanced CT
- There is no evidence to suggest that contrast-enhanced CT is necessary for diagnosing renal stones 2, 6, 3, 5, 4
- Non-contrast CT scan is sufficient for detecting stones and guiding appropriate treatment 3
- Contrast-enhanced CT may not be necessary, and non-contrast CT or ultrasonography may be preferred to reduce radiation exposure 6