From the Guidelines
The radiological investigation of choice for patients with suspected renal stones is a non-contrast CT scan of the abdomen and pelvis, also known as a CT KUB (kidney, ureter, bladder). This imaging modality is preferred because:
- It has high sensitivity and specificity for detecting renal stones, including small stones that may be missed by other imaging techniques, with a reported sensitivity as high as 97% 1.
- It can accurately determine the size, location, and number of stones, which is crucial for treatment planning, and stone location and size can be accurately depicted at noncontrast CT 1.
- It does not require intravenous contrast, reducing the risk of allergic reactions and kidney injury.
- It can identify alternative diagnoses that may mimic renal colic symptoms.
- It is relatively quick to perform and widely available in most hospital settings. While a plain abdominal X-ray (KUB) can detect some stones, it is less sensitive and may miss radiolucent stones, with a sensitivity of only 72% for large stones and 29% overall for the detection of stones of any size in any location 1. An abdominal ultrasound can be useful as an initial screening tool, especially in pregnant patients or children, but it is less accurate than CT for definitive diagnosis and treatment planning. When ordering a CT for renal stones, specify "non-contrast CT KUB" to ensure the appropriate protocol is used, and the radiation dose should be kept as low as reasonably achievable while maintaining diagnostic quality, with low-dose CT having a pooled sensitivity of 97% and a pooled specificity of 95% 1.
From the Research
Radiological Investigation for Nephrolithiasis
The radiological investigation of choice for patients with nephrolithiasis (renal stones) is a crucial aspect of diagnosis and management. The following points highlight the key findings:
- Computed Tomography (CT) is considered the gold standard for diagnosing stone disease due to its high accuracy 2, 3, 4.
- CT scans have high sensitivity and specificity for detecting renal calculi, but they are associated with radiation hazards and high costs 2.
- Ultrasonography (US) is a cheaper and safer alternative, but it has limited sensitivity and specificity, particularly for small stones (<3 mm) and in nondilated systems 2, 5.
- The sensitivity and specificity of US for detecting renal calculi are around 45-54% and 88-91%, respectively 2, 5.
- Newer modes and techniques, such as photon-counting detector CT, can improve the accuracy of stone size measurement and detection, especially for small stones 6.
- Spiral CT has been shown to be superior to other imaging methods, including plain abdominal films, tomography, and ultrasonography, for detecting residual renal calculi 4.
Comparison of Imaging Modalities
The following points compare the different imaging modalities:
- CT is more sensitive and specific than US for detecting renal calculi, but US is cheaper and safer 2, 5.
- Photon-counting detector CT is more sensitive than conventional energy-integrating detector CT for detecting small renal stones 6.
- Spiral CT is superior to other imaging methods for detecting residual renal calculi, with a sensitivity of 100% 4.
- The choice of imaging modality depends on the specific clinical scenario and the availability of resources 3.