What is the role of Computed Tomography (CT) scans with or without intravenous contrast in diagnosing kidney stones (nephrolithiasis)?

From the Guidelines

Non-contrast CT scans are the gold standard for diagnosing kidney stones due to their high sensitivity and ability to clearly identify calcifications without the need for intravenous contrast material. This approach is preferred because kidney stones are naturally dense and appear bright on CT images without any enhancement needed, as noted in the study by 1. The use of non-contrast CT scans also reduces the risk of contrast-induced nephropathy, which is particularly important in patients with kidney stones who may already have compromised renal function.

Key Points to Consider

• Non-contrast CT scans can detect stones as small as 1-2 mm with high sensitivity (95-98%) 2.
• The typical protocol for kidney stone evaluation is a non-contrast helical CT scan of the abdomen and pelvis, which can provide information about stone size, location, and degree of urinary tract obstruction, all of which help guide treatment decisions.
• Contrast may be added in specific situations, such as when there's suspicion of complicated infection, abscess formation, or when evaluating for other urinary tract abnormalities that might be causing obstruction.
• Low-dose non-contrast CT scans have been shown to have a pooled sensitivity of 97% and a pooled specificity of 95% for detecting urolithiasis, making them a viable option for patients, especially young ones, to reduce radiation exposure 2.

Clinical Recommendations

• For patients with acute onset of flank pain and suspicion of stone disease without known prior stone disease, non-contrast CT (NCCT) is the imaging study of choice for initial evaluation, as recommended by 1 and 3.
• For patients with known disease and recurrent symptoms of urolithiasis, NCCT remains the test of choice for follow-up imaging, as stated in 1 and 3.
• In pregnant patients with acute onset flank pain and suspicion of stone disease, ultrasound is usually appropriate for initial or follow-up imaging, as noted in 3.

From the Research

Role of Computed Tomography (CT) Scans in Diagnosing Kidney Stones

• CT scans with or without intravenous contrast are commonly used to diagnose kidney stones (nephrolithiasis) 4, 5, 6, 7
• Non-contrast CT scans are considered the gold standard for detecting kidney stones, with a detection rate of over 99% 7
• The use of intravenous contrast in CT scans does not significantly increase the risk of acute kidney injury (AKI) in patients with normal renal function 4

Advantages and Disadvantages of CT Scans

• Advantages:
  • High sensitivity and specificity for detecting kidney stones 5, 7
  • Can provide detailed images of the kidneys, ureters, and bladder 5
• Disadvantages:
  • Exposes patients to ionizing radiation 5, 6
  • May not be necessary for all patients with suspected renal colic 6

Alternative Imaging Modalities

• Ultrasonography is a viable alternative to CT scans, especially for patients who cannot undergo CT scans or have a high risk of radiation exposure 5, 6, 7
• Plain film radiography can be used for follow-up of radiopaque stones, but is limited in sensitivity and specificity 7
• MRI provides the possibility of 3D imaging without exposure to radiation, but is costly and currently has limited availability for kidney stone detection 5

Low-Dose CT Scans

• Low-dose CT scans can be used to reduce radiation exposure while maintaining diagnostic accuracy 8
• Ultra-low-dose CT scans have a good detection rate for all kinds of stones, even when the fragment size is small 8
• The minimum radiation dose capable of detecting stone fragments may vary depending on stone composition 8