Is a CT of the abdomen and pelvis with IV contrast appropriate for a patient with persistent left lower back pain and minimal bilateral hydronephrosis after a treated UTI?

CT Abdomen and Pelvis with IV Contrast for Persistent Left Lower Back Pain with Minimal Bilateral Hydronephrosis

CT abdomen and pelvis with IV contrast is appropriate and recommended for this patient with persistent left lower back pain, minimal bilateral hydronephrosis, and negative follow-up tests after treated UTI. 1

Rationale for CT with IV Contrast

• CT abdomen and pelvis with IV contrast provides comprehensive evaluation of minimal hydronephrosis with unknown cause and is particularly useful for patients with persistent symptoms 2, 1
• The addition of IV contrast is helpful in assessment for pelvic masses and other potential causes of bilateral hydronephrosis that may not be visible on ultrasound 2
• In patients with flank pain and negative urinalysis without history of urolithiasis, CT abdomen and pelvis with IV contrast identified clinically significant diagnoses in 15% of cases 2, 1
• Contrast-enhanced CT has approximately 30% higher diagnostic accuracy compared to non-contrast CT for evaluating abdominal pain 3

Clinical Considerations for This Patient

• Persistent symptoms after treated UTI with negative follow-up tests suggests a need for more comprehensive imaging beyond ultrasound 1
• Minimal bilateral hydronephrosis without visible stones on renal ultrasound requires further investigation to determine etiology 2
• Normal CBC and CMP suggest absence of active infection or significant renal dysfunction, making IV contrast administration appropriate 1
• Left lower back pain localization may indicate a specific pathology that requires detailed anatomical imaging 2

Benefits of IV Contrast in This Scenario

• Administration of IV contrast for CT abdomen and pelvis is associated with increased detection of urgent findings compared with non-contrast CT (p=0.004) 4
• IV contrast-enhanced CT can better characterize both urgent and non-urgent findings compared to non-contrast studies 4
• Contrast enhancement allows better visualization of vascular structures and characterization of various disease entities in the peripancreatic region 5
• Adherence to ACR appropriateness criteria for IV contrast administration increases detection of urgent pathology and may avoid short-term repeat CT examinations 4

Alternative Imaging Considerations

• CT without IV contrast would be appropriate if obstructive urolithiasis is the primary concern, but this is less likely given the bilateral nature of the hydronephrosis and negative ultrasound for stones 2
• MR urography could be considered as an alternative if the patient has contraindications to iodinated contrast 1
• Renal scintigraphy (MAG3 scan) might be appropriate if functional assessment of obstruction is needed, particularly if CT findings are equivocal 2

Potential Pitfalls and Caveats

• Ensure the patient has no contraindications to IV contrast (e.g., severe renal impairment, contrast allergy) 1
• Bladder distension can cause mild hydronephrosis in normal individuals, so ensure the patient has voided before kidney scanning to avoid artifactual hydronephrosis 1
• If CT imaging is negative but hydronephrosis persists on follow-up ultrasound, consider repeat evaluation within 3-5 years 1
• For persistent or recurrent hydronephrosis after negative initial workup, additional evaluation may be needed 1

CT with IV contrast represents the most comprehensive initial imaging approach for this clinical scenario, offering superior diagnostic accuracy and the best chance to identify the cause of persistent symptoms and minimal bilateral hydronephrosis.