Should a computed tomography (CT) scan be ordered to better assess a 0.3cm asymptomatic renal calculus in a patient with low back pain and normal urinalysis?

CT Imaging is NOT Indicated for a 0.3cm Asymptomatic Renal Calculus with Normal Urinalysis

A CT scan should not be ordered for this patient, as a 0.3cm asymptomatic renal stone with normal urinalysis and low back pain does not meet criteria for advanced imaging and the stone is likely incidental to the back pain.

Why CT is Not Appropriate in This Clinical Scenario

The Stone is Likely Incidental to the Back Pain

• Contrast-enhanced CT abdomen/pelvis identifies clinically significant non-urological diagnoses in 15% of patients with flank/back pain and negative urinalysis, suggesting the back pain has an alternative etiology 1
• The normal urinalysis makes obstructive uropathy or infected stone extremely unlikely, as these conditions typically produce hematuria or pyuria 1
• A 0.3cm (3mm) stone is below the threshold that typically causes symptoms or obstruction 2

Small Asymptomatic Stones Do Not Require CT Imaging

• The American College of Radiology states that CT is not appropriate in the initial evaluation of isolated nonpainful hematuria, and this principle extends to asymptomatic stones discovered incidentally 3
• Stones <5mm have high spontaneous passage rates and do not require intervention planning 2
• CT imaging should be reserved for symptomatic patients with moderate-to-severe hydronephrosis where stone size, location, and density are needed for surgical planning 3, 2

What Should Be Done Instead

Address the Back Pain Appropriately

• Perform straight-leg raise testing and brief neurological exam to assess for radiculopathy if back pain radiates to the legs 1
• Check for red flags including history of cancer, unexplained weight loss, age over 50, fever, or progressive neurological deficits 1
• Consider musculoskeletal causes as the primary etiology, particularly vertebral compression fracture in older patients or those with osteoporosis risk 1

Manage the Small Renal Stone Conservatively

• No imaging is indicated for asymptomatic microscopic hematuria without proteinuria or dysmorphic red blood cells, and this applies equally to incidentally discovered small stones 3
• Ensure adequate hydration and consider screening for hypercalciuria or hyperuricosuria if there is concern for stone recurrence 3
• Follow-up ultrasound in 1-6 months can confirm stone passage or stability if clinical concern persists, avoiding radiation exposure 1

Critical Pitfalls to Avoid

• Do not assume the back pain is caused by the small stone simply because it was found on imaging - correlation does not equal causation, and a 3mm stone rarely causes pain 1
• Avoid unnecessary radiation exposure from CT scanning when clinical findings do not support obstructive uropathy - the normal urinalysis is reassuring 3, 1
• Do not delay evaluation of the actual back pain etiology by focusing on an incidental radiographic finding - the patient's symptoms require appropriate musculoskeletal assessment 1

When CT Would Be Indicated

• If the patient develops acute flank pain with hematuria suggesting stone movement or obstruction 2
• If follow-up imaging shows stone growth or development of hydronephrosis 2
• If symptoms fail to respond to conservative management and urological intervention is being considered 2
• If moderate-to-severe hydronephrosis develops, as this predicts need for urological intervention with high likelihood 2