From the Guidelines
Noncontrast CT (NCCT) is the imaging study of choice for initial evaluation of patients with acute onset of flank pain and suspicion of stone disease. This recommendation is based on the most recent and highest quality study available, which emphasizes the reliability of NCCT in characterizing the location and size of an offending ureteral calculus, identifying complications, and diagnosing alternative etiologies of abdominal pain 1. The use of NCCT allows for precise measurement and clear depiction of stone location, making it invaluable in guiding treatment decisions.
Alternative Imaging Options
While NCCT is the preferred first-line test, other imaging modalities may be considered in specific contexts:
- Ultrasound may have a role in evaluating for signs of obstruction, particularly in patients where radiation exposure is a concern, such as pregnant patients 1.
- Radiography, although less sensitive than NCCT, may still have a role in certain situations, such as follow-up for radio-opaque stones 1.
- Low-dose CT protocols can be used to reduce radiation exposure in patients with recurrent stones, maintaining diagnostic accuracy while minimizing risks 1.
Clinical Considerations
The choice of imaging should be guided by the clinical presentation, with NCCT being most valuable in acute settings where diagnosis is uncertain. In contrast, ultrasound may be more appropriate for follow-up or in pregnant patients due to its lack of radiation exposure. It's also important to consider the potential risks associated with imaging tests, such as radiation exposure from CT scans, and to use low-dose regimens when possible to mitigate these risks 1.
Key Points
- NCCT is the preferred initial imaging test for suspected kidney stones due to its high sensitivity and specificity.
- Ultrasound and radiography have specific roles, particularly in pregnant patients or for follow-up of certain types of stones.
- Low-dose CT protocols can reduce radiation exposure without compromising diagnostic accuracy in patients with recurrent stones.
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 has been found to have equivalent diagnostic accuracy to CT in some studies 2, 3
- Kidney, ureter, bladder (KUB) plain film radiography is helpful in evaluating interval stone growth in patients with known stone disease 2
- MRI provides 3D imaging without radiation but is costly and currently has difficulty visualizing stones 2
- Dual-energy CT enables accurate characterization of stone disease and helps direct therapy 4
Comparison of Imaging Modalities
- A randomized controlled trial compared ultrasonography and CT and found no significant difference in high-risk diagnoses with complications, serious adverse events, pain scores, return emergency department visits, or hospitalizations 3
- Ultrasonography was associated with lower cumulative radiation exposure than CT 3
- Guidelines recommend non-contrast CT as the initial imaging modality, but also endorse ultrasonography as a viable alternative 5
Special Considerations
- In pregnant women and children, renal US is recommended as the initial imaging modality, but low-dose CT scans may also be safe 6
- Intraoperative imaging by fluoroscopy or US assists with surgical intervention 6
- Posttreatment imaging is recommended to ensure complete fragmentation and stone clearance 6