What imaging modalities are used to diagnose kidney stones (nephrolithiasis)?

From the Guidelines

For kidney stone imaging, non-contrast CT scan is the preferred first-line test due to its high sensitivity and specificity for detecting stones, as reported in the 2023 study by the Journal of the American College of Radiology 1. This recommendation is based on the high accuracy of non-contrast CT in detecting renal calculi, with a reported sensitivity as high as 97% 1. The use of non-contrast CT allows for rapid acquisition with high spatial resolution and ability for multiplanar reformations, which can also visualize secondary signs of urolithiasis and complications such as periureteral and perinephric inflammation and ureteral dilatation.

Some key benefits of non-contrast CT include:

• High sensitivity and specificity for detecting stones
• Ability to identify stone size, location, and density, which helps guide treatment decisions
• Rapid acquisition with high spatial resolution and ability for multiplanar reformations
• Visualization of secondary signs of urolithiasis and complications

Low-dose non-contrast CT protocols can also provide adequate imaging while reducing radiation exposure, which is particularly important for young patients or those with recurrent stones 1. The choice of imaging should consider the patient's clinical presentation, pregnancy status, history of recurrent stones, and radiation exposure concerns. Prompt imaging is important for patients with severe pain, fever, or single kidney to guide appropriate management.

From the Research

Imaging Modalities for Kidney Stones

• Ultrasonography (US) is a commonly used imaging modality for detecting renal calculi, with a sensitivity of 54% and specificity of 91% 2
• However, US has limitations in sizing stones accurately, particularly for stones in the 0-10 mm range, which can lead to inappropriate counseling in 14% of cases 2
• The use of plain abdominal film of kidney, ureter, and bladder (KUB) and US can increase sensitivity to 78%, but 37% of patients may still be counseled inappropriately 2

Computed Tomography (CT) for Kidney Stones

• Non-contrast CT is widely regarded as the gold standard for diagnosis of urolithiasis, but it can be costly and exposes patients to significant doses of ionizing radiation 3
• Dual-energy CT enables more accurate characterization of stone disease and helps direct therapy at the time of the initial imaging evaluation 4
• Low-dose (LD) and ultra-low-dose (ULD) CT protocols have been developed to reduce radiation exposure while maintaining diagnostic accuracy, with sensitivity ranging from 90 to 98% for LD CT and 72 to 99% for ULD CT 5

Ultrasound for Kidney Stones

• Bedside ultrasound can detect hydronephrosis, a sign of ureteral stone, with a sensitivity of 78.4% and specificity of 82.4% 3
• The sensitivity of ultrasound for detecting hydronephrosis increases with stone size, with a sensitivity of 90% for stones ≥6 mm 3
• Ultrasound can be used to guide clinical decision-making for residual or asymptomatic calculi, but its limitations in sizing stones accurately and low sensitivity can lead to inappropriate counseling 2

Novel Imaging Protocols

• The DRINK protocol, which includes oral hydration and an oral diuretic, can increase the distention of the renal collecting system and improve preoperative planning for kidney stone treatment 6
• This protocol has been shown to increase the visible collecting system volume and surface area, and can help identify patients who may benefit from medical expulsive therapy 6