What is the recommended imaging modality for diagnosing kidney stones?

From the Guidelines

The recommended imaging modality for diagnosing kidney stones is a non-contrast computed tomography (CT) scan of the abdomen and pelvis. This is considered the gold standard due to its high sensitivity and specificity for detecting urinary stones, as supported by the most recent study from 2023 1. CT scans can identify stones of all compositions, determine their exact size and location, and assess for complications such as obstruction or infection.

Key Considerations

• For pregnant patients or children, ultrasound is the preferred initial imaging modality to avoid radiation exposure, though it has lower sensitivity compared to CT, as noted in the study by Gupta et al 1.
• Low-dose CT protocols have been developed that reduce radiation exposure while maintaining diagnostic accuracy.
• X-ray (KUB) and intravenous pyelogram (IVP) are older techniques with limited sensitivity, particularly for non-calcium containing stones, as discussed in the study by Innes et al 1.
• CT scans also provide additional information about alternative diagnoses that may mimic renal colic, making them particularly valuable in emergency settings when the diagnosis is uncertain, as highlighted in the study by Abdel-Gawad et al 1.

Special Considerations

• In patients with known current stone disease, diagnosed on recent imaging, with recurrent symptoms of stone disease, CT abdomen and pelvis without IV contrast is usually appropriate as the follow-up imaging, as recommended by the study by Gupta et al 1.
• For patients with acute onset flank pain and suspicion of stone disease, CT abdomen and pelvis without IV contrast is usually appropriate for the initial imaging, as supported by the study by Gupta et al 1.

Imaging Modalities

• Non-contrast CT scan of the abdomen and pelvis: high sensitivity and specificity for detecting urinary stones.
• Ultrasound: preferred initial imaging modality for pregnant patients or children, but with lower sensitivity compared to CT.
• X-ray (KUB) and intravenous pyelogram (IVP): older techniques with limited sensitivity, particularly for non-calcium containing stones.

From the Research

Recommended Imaging Modalities for Diagnosing Kidney Stones

• Noncontrast CT of the abdomen and pelvis is consistently considered the most accurate diagnosis for kidney stones, but it exposes patients to ionizing radiation 2, 3.
• Ultrasonography has a lower sensitivity and specificity than CT, but does not require the use of radiation and has been found to have equivalent diagnostic accuracy to CT in some studies 2.
• Kidney, ureter, bladder (KUB) plain film radiography is most helpful in evaluating for interval stone growth in patients with known stone disease, but is less useful in the setting of acute stones 2.
• MRI provides the possibility of 3D imaging without exposure to radiation, but is costly and currently has limitations in visualizing stones 2.

Considerations for Choosing an Imaging Modality

• The choice of imaging modality should be based on the individual patient's needs and the clinical context, taking into account factors such as radiation exposure and diagnostic accuracy 4, 3.
• CT is the preferred method for the evaluation and treatment planning of urolithiasis, but efforts should be made to reduce radiation dose, such as using low-dose CT protocols 3, 5.
• Conventional radiography and ultrasound are still recommended for follow-up of renal stones, particularly in patients with known stone disease 3.

Reducing Radiation Exposure

• Limiting the cranial extent of CT KUB imaging to the T10 vertebral level can reduce radiation dose while maintaining diagnostic accuracy 5.