From the Guidelines
For patients with suspected kidney stones, a non-contrast CT scan of the abdomen and pelvis is the recommended first-line imaging test. This recommendation is based on the high sensitivity (up to 97%) and specificity of non-contrast CT for detecting renal calculi, as reported in a recent study published in the Journal of the American College of Radiology 1. The use of non-contrast CT allows for accurate detection of even small stones, as well as visualization of secondary signs of urolithiasis and complications such as periureteral and perinephric inflammation and ureteral dilatation.
Some key benefits of non-contrast CT include:
- High spatial resolution and ability for multiplanar reformations
- Ability to accurately assess stone size, location, and density, which is important for planning urologic management
- Low-dose protocols can reduce radiation exposure while maintaining diagnostic accuracy, making it a suitable option for patients with concerns about radiation exposure 1
- Can identify predictors of the need for invasive management, such as larger stone size and higher density
In certain situations, alternative imaging options may be considered, such as:
- Ultrasound, which may be used for pregnant patients or when radiation exposure is a concern, although it has lower sensitivity (45-90%) compared to CT
- X-ray (KUB), which may be used for follow-up of radio-opaque stones, but has lower sensitivity and misses uric acid stones
Overall, the choice of imaging test should be guided by the individual patient's needs and circumstances, with non-contrast CT being the preferred initial test for most patients with suspected kidney stones 1.
From the Research
Imaging Modalities for Kidney Stones
- Noncontrast CT of the abdomen and pelvis provides the most accurate diagnosis but exposes patients to ionizing radiation 2
- Ultrasonography has a lower sensitivity and specificity than CT but does not require radiation, and its diagnostic accuracy is equivalent to CT in the emergency department setting 2
- Kidney, ureter, bladder (KUB) plain film radiography is helpful in evaluating interval stone growth but less useful in acute stone settings 2
- MRI offers 3D imaging without radiation but is costly and has difficulty visualizing stones 2
Diagnostic Accuracy of Imaging Modalities
- Ultrasonography has a sensitivity of 54% and specificity of 91% for detecting renal calculi, with significant association between sensitivity and stone size 3
- Ultrasonography tends to overestimate stone size, particularly in the 0-10 mm range, which can lead to inappropriate counseling for intervention or observation 3
- The use of plain abdominal film of kidney, ureter, and bladder with ultrasonography increases sensitivity to 78% but may still result in inappropriate counseling in 37% of cases 3
Advances in Imaging Techniques
- Dual-energy CT enables more accurate characterization of stone disease and helps direct therapy at the initial imaging evaluation 4
- A novel protocol using oral hydration and a diuretic (DRINK protocol) can enhance collecting system distention in non-contrast computed tomography for kidney stones, allowing for better preoperative planning 5
- Low-dose and ultra-low-dose CT scans maintain high diagnostic accuracy, sensitivity, and specificity for identifying urinary tract stones while reducing radiation exposure 6