What is the best imaging and treatment approach for a suspected kidney stone in an adult patient with a history of urinary tract issues?

Imaging for Suspected Kidney Stone

Order a non-contrast CT of the abdomen and pelvis as the initial imaging study for an adult patient with suspected kidney stone. This is the gold standard with the highest diagnostic accuracy and provides critical information about stone size, location, and density needed for management decisions 1, 2.

Primary Imaging Recommendation

Non-contrast CT abdomen and pelvis is the definitive first-line imaging modality with sensitivity up to 97% and specificity of 95% 2, 3. This study:

• Accurately detects stone location, size, and density—all critical factors determining whether the patient needs intervention versus conservative management 1
• Identifies secondary signs of obstruction including hydronephrosis and perinephric stranding 1
• Detects alternative diagnoses that may mimic renal colic 1
• Should be performed using low-dose protocols to minimize radiation exposure while maintaining diagnostic accuracy 2, 4

Key Technical Points

• Include the entire pelvis in the scan field to detect distal ureteral stones and bladder abnormalities 1
• Use coronal reformations, bone windows, and magnified views to improve accuracy of stone measurements 1
• No IV contrast is needed for stone detection—contrast does not improve diagnostic accuracy for urolithiasis and adds unnecessary cost and risk 1

Alternative Imaging Options

Ultrasound of Kidneys and Bladder

Ultrasound is an acceptable alternative with appropriateness rating of 7, particularly useful for:

• Pregnant patients—ultrasound should be first-line with appropriateness rating of 8 2
• Patients requiring multiple repeat imaging studies to reduce cumulative radiation exposure 2
• Detecting hydronephrosis—ultrasound has sensitivity up to 100% for obstruction 5

Critical limitations of ultrasound alone:

• Significantly reduced accuracy for stones <3mm 2
• Lower sensitivity for detecting stones in non-dilated systems 2, 5
• Absence of hydronephrosis does NOT rule out kidney stones (negative predictive value only 65%) 2
• Missed 60% of acute pyelonephritis cases compared to CT in one study 1

Combined Ultrasound + KUB Radiography

This combination improves sensitivity compared to either modality alone while reducing radiation exposure 2. However:

• KUB has limited utility for acute stone diagnosis 1
• KUB is most helpful for tracking known radiopaque stones over time 2, 3
• Stone visibility depends on composition and patient body habitus 2

Special Clinical Scenarios

Pregnant Patients

Use ultrasound as first-line imaging (appropriateness rating 8) 2. If ultrasound is inconclusive:

• MRI without contrast is the second-line option 2
• Low-dose non-contrast CT should only be used as last resort 2

Recurrent Stone Formers

For patients with history of multiple stones requiring repeated imaging:

• Review previous images to understand stone history and patterns 2
• Limit CT scan field to the specific area of interest 2
• Consider ultrasound for follow-up when clinically appropriate 2
• Use the lowest possible radiation dose for necessary CT scans 2

Complicated Patients

For patients with diabetes, immunocompromise, recurrent pyelonephritis, or lack of response to initial therapy:

CT abdomen and pelvis WITH IV contrast is recommended to:

• Detect parenchymal changes of acute pyelonephritis (sensitivity 84% vs 1.4% for non-contrast) 1
• Identify renal or perirenal abscesses (detection rate 4% on CT vs 1.1% on ultrasound) 1
• Rule out alternative acute conditions (cholecystitis, appendicitis, liver abscess) that may present similarly 1

Common Pitfalls to Avoid

• Do not order CTU (CT urography with contrast) for acute stone evaluation—there is no evidence that the excretory phase improves diagnostic accuracy for urolithiasis 1
• Do not skip the pelvis—distal ureteral and bladder stones will be missed 1
• Do not rely on ultrasound alone in non-pregnant adults—the miss rate is too high for definitive management decisions 2, 5
• Do not order MRI for routine stone evaluation—it is costly and stones are difficult to visualize (only 50% detection rate at 3T) 1, 3

Treatment Planning Based on Imaging

Once imaging is obtained, stone characteristics guide management:

• Stones <5mm typically pass spontaneously within 3 days in most patients 6, 7
• Larger, more proximal stones have higher need for intervention 1
• Stone size and density predict need for invasive management 1
• Medical expulsive therapy should be considered for appropriate candidates 7, 8