What is the recommended initial imaging test for suspected ureteral (ureter) stone?

Recommended Imaging for Suspected Ureteral Stone

Non-contrast CT scan of the abdomen and pelvis is the recommended initial imaging test for suspected ureteral stones, with sensitivity and specificity exceeding 95%. 1

Rationale for Non-Contrast CT as First-Line Imaging

Non-contrast CT is considered the reference standard for evaluating urolithiasis for several key reasons:

• Highest diagnostic accuracy with sensitivity up to 97% 1
• Allows precise measurement of stone size and location 2
• Provides clear depiction of where in the ureter a stone has become lodged 2
• Visualizes secondary signs of obstruction such as ureteral dilatation and perinephric inflammation 2
• Virtually all renal calculi are radiopaque on CT 2

Low-Dose Protocol Recommendation

A low-dose CT protocol should be used instead of conventional dosing to minimize radiation exposure:

• Low-dose (<3 mSv) CT maintains excellent diagnostic performance with pooled sensitivity of 97% and specificity of 95% 1
• Reduces radiation exposure by approximately 50% while providing equivalent stone measurements to standard-dose CT 1, 3
• Intraobserver and interobserver agreements are excellent with kappa values ranging from 0.87 to 0.98 3

Special Populations

• Pregnant patients: Ultrasonography is the imaging tool of choice 2
• Children and young adults: Low-dose CT protocol is particularly important to minimize radiation exposure 1

Clinical Significance of Stone Characteristics

CT findings help determine management approach:

• Stone size and location are essential for determining the level of intervention required 2
• Smaller (<5mm), more proximal stones are more likely to pass spontaneously 2, 1
• Larger stone size (>6mm) and higher density measured at CT have been shown to be predictors of the need for invasive management 2

Alternative Imaging Options

When CT is not available or contraindicated:

• Ultrasound combined with abdominal radiography has a sensitivity of about 79% in identifying clinically significant stones 2
• Ultrasound alone has lower sensitivity (45%) but good specificity (88%) 1
• MRI is less accurate for identifying suspected stones but is highly dependable in depicting hydronephrosis and perinephric edema 2

Common Pitfalls to Avoid

1. Using contrast-enhanced CT as first-line: IV contrast may obscure stones within the renal collecting system 1
2. Relying solely on abdominal radiography: Has limited sensitivity (~49%) and may lead to repeat imaging, negating radiation reduction benefits 2, 1
3. Inadequate stone measurement technique: Use coronal reformations, bone window settings, and magnified views for accurate stone measurements 2
4. Missing small stones: Sensitivity decreases with smaller stone size, especially with increasing dose reduction 2

Non-contrast CT provides the most accurate assessment of stone burden and location, which are critical factors in determining appropriate management and predicting the likelihood of spontaneous passage.