What is the initial imaging study for nephrolithiasis (kidney stones)?

From the Guidelines

The first imaging study typically used for kidney stones is a non-contrast computed tomography (CT) scan of the abdomen and pelvis. This is considered the gold standard for diagnosing kidney stones due to its high sensitivity and specificity, as noted in the most recent guidelines 1. A CT scan can quickly identify the size, number, and location of stones, which helps guide treatment decisions. It can also detect complications such as obstruction or infection. The scan takes only minutes to perform and doesn't require contrast material, which avoids potential allergic reactions and is safer for patients with kidney dysfunction.

Key Considerations

• Non-contrast CT is the imaging study of choice for initial evaluation of patients with acute onset of flank pain and suspicion of stone disease without known prior stone disease, as stated in the American College of Radiology guidelines 1.
• Ultrasound may have a role in evaluating for signs of obstruction, particularly in patients where radiation exposure is a concern, such as pregnant women or young patients 1.
• Radiography (KUB - kidney, ureter, bladder) may sometimes be used for follow-up imaging but is not typically the first choice due to its limited ability to detect many types of stones 1.

Evidence-Based Recommendations

• The American College of Radiology recommends non-contrast CT as the initial imaging study for patients with suspected kidney stones 1.
• Ultrasound is a suitable alternative for patients where radiation exposure is a concern, but it is less sensitive than CT 1.
• The combination of ultrasound and radiography may be used as an alternative to CT, but it has decreased detection rates for smaller stones [<5 mm] 1.

Clinical Implications

• The choice of imaging study should be based on the individual patient's needs and circumstances, taking into account factors such as radiation exposure and kidney function.
• Non-contrast CT is generally the preferred initial imaging study for kidney stones due to its high sensitivity and specificity, but ultrasound and radiography may be used in certain situations.

From the Research

Initial Imaging Study for Nephrolithiasis

The initial imaging study for nephrolithiasis (kidney stones) is a crucial step in diagnosis and treatment. The following points highlight the recommended imaging modalities:

• Noncontrast CT of the abdomen and pelvis is considered the most accurate diagnostic tool for nephrolithiasis, providing high sensitivity and specificity 2, 3.
• Ultrasonography is also a commonly used imaging modality, especially in patients where radiation exposure is a concern, such as pregnant women or children 2, 4.
• Kidney, ureter, bladder (KUB) plain film radiography is helpful in evaluating interval stone growth in patients with known stone disease, but less useful in the setting of acute stones 2.
• MRI provides the possibility of 3D imaging without exposure to radiation, but is currently costly and has limitations in visualizing stones 2.

Specific Recommendations

• For adult patients, noncontrast CT is recommended as the first-line imaging modality for suspected obstructive nephrolithiasis 3.
• For pediatric patients, ultrasound is recommended as the first-line imaging modality, with non-contrast CT as a second-line option 4.
• A proposed algorithm for imaging patients with acute stones takes into account the current guidelines and randomized controlled trials, aiding clinicians in making informed decisions 2.

Advantages and Disadvantages of Imaging Modalities

• Noncontrast CT: high sensitivity and specificity, but exposes patients to ionizing radiation 2, 3.
• Ultrasonography: lower sensitivity and specificity than CT, but does not require radiation exposure 2, 4.
• MRI: costly and limited in visualizing stones, but provides 3D imaging without radiation exposure 2.