Can an adult patient with left and right flank pain be evaluated with an ultrasound to diagnose the underlying cause of their symptoms?

Can Ultrasound Be Used to Evaluate Bilateral Flank Pain?

For adult patients with bilateral (left and right) flank pain, ultrasound is not the recommended first-line imaging modality—noncontrast CT is the imaging study of choice for initial evaluation when stone disease or acute obstruction is suspected. 1

Primary Recommendation

Noncontrast CT (NCCT) should be ordered as the initial imaging test for patients presenting with acute bilateral flank pain, as it reliably characterizes stone location and size, identifies complications, and diagnoses alternative etiologies with sensitivity and specificity approaching 98-100%. 1, 2

Why CT Over Ultrasound for Flank Pain

The American College of Radiology Appropriateness Criteria explicitly designates NCCT as the imaging study of choice for acute onset flank pain with suspicion of stone disease. 1 This recommendation is based on several critical advantages:

• NCCT detects ureteral stones with 98-100% sensitivity and specificity regardless of size, location, or chemical composition 2, 3
• CT identifies extraurinary causes of flank pain in approximately one-third of patients presenting with acute flank pain 2
• The examination is completed within 5 minutes without requiring contrast agents 2
• CT provides precise determination of stone size and location, the two most important factors for patient management 3

Limited Role of Ultrasound in Flank Pain

While ultrasound has some utility, it has significant limitations for evaluating acute flank pain:

• Ultrasound is less sensitive than CT for detecting stones, with diagnostic accuracy of only 66% compared to 85% for urography in acute flank pain 4
• Ultrasound may have a role in evaluating for signs of obstruction (hydronephrosis), but is not as sensitive as CT for diagnosing acute obstruction 1, 5
• Ultrasound is not useful for evaluating patients with acute flank pain when acute obstruction may be present 5
• When combined with findings of pyeloureteral dilatation, direct visualization of stones, and absence of ureteral ejaculation, ultrasound sensitivity can reach 96%, but this requires optimal conditions 2

When Ultrasound May Be Appropriate

There are specific clinical scenarios where ultrasound becomes the preferred initial modality:

• In pregnant patients, ultrasound is recommended as the initial modality of choice due to radiation concerns, with potential role for noncontrast MRI if ultrasound is inconclusive 1
• Ultrasound is a viable alternative in patients with recurrent renal colic due to known stone disease 4
• For young patients where radiation exposure is a significant concern, ultrasound may be considered as initial imaging 6

Clinical Algorithm for Bilateral Flank Pain Imaging

Step 1: Determine if patient is pregnant or has known recurrent stone disease

• If pregnant → Order ultrasound first 1
• If known recurrent stones → Ultrasound may be acceptable 4
• If neither → Proceed to Step 2

Step 2: Order noncontrast CT as first-line imaging 1

Step 3: If NCCT is inconclusive and stone disease still suspected → Consider contrast-enhanced imaging with MRI or CT urogram 1

Common Pitfalls to Avoid

• Do not rely on ultrasound as the primary imaging modality for acute bilateral flank pain in non-pregnant adults, as it will miss significant pathology in up to 34% of cases 4
• Do not assume that bilateral presentation changes the imaging approach—NCCT remains the study of choice regardless of whether pain is unilateral or bilateral 1
• Do not order plain radiography as initial imaging, as it has limited diagnostic value with sensitivity of only 40-60% for direct stone detection 2
• Do not delay appropriate CT imaging in favor of ultrasound simply to avoid radiation, except in pregnancy or pediatric patients 1

Special Considerations

For patients with contraindications to CT (severe contrast allergy if contrast needed, pregnancy), the imaging hierarchy shifts to ultrasound followed by MRI if ultrasound is non-diagnostic. 1 However, for the standard adult patient with acute bilateral flank pain and no contraindications, NCCT should be ordered without attempting ultrasound first, as this approach provides the most rapid, accurate, and comprehensive evaluation. 1, 3