What is the best approach to manage a patient with right flank pain, without fever or dysuria?

Management of Right Flank Pain Without Fever or Dysuria

Order a non-contrast CT of the abdomen and pelvis as the initial imaging study, as it provides the highest diagnostic accuracy (98-100% sensitivity and specificity) for detecting urinary stones and identifies alternative causes of flank pain in approximately one-third of patients. 1

Initial Imaging Approach

First-Line Imaging: Non-Contrast CT

• Non-contrast CT abdomen and pelvis is the gold standard for evaluating acute flank pain, detecting urinary stones regardless of size, location, or chemical composition with near-perfect accuracy 1, 2
• This modality identified stones in 32.7% of patients and revealed alternative non-calculus pathology in 32% of stone-negative cases 3
• In a study of 89 patients with adequate follow-up, non-contrast CT demonstrated 98% sensitivity, 100% specificity, 100% positive predictive value, and 97% negative predictive value for detecting obstructing ureteral calculi 2

Alternative: Ultrasound in Select Populations

• Consider ultrasound as first-line imaging only in specific circumstances: pregnant patients, those with radiation concerns, patients with known renal disease, or when hydronephrosis has already been identified 1
• Moderate to severe hydronephrosis on ultrasound in patients with moderate or high risk of ureteric calculi can provide sufficient diagnostic information without immediate CT 4, 1
• However, the absence of hydronephrosis on ultrasound does NOT rule out ureteral stones (negative predictive value only 65%), though it makes larger stones less likely 4, 1

Key Diagnostic Considerations

When CT Reveals Hydronephrosis

• Any degree of hydronephrosis on imaging increases the likelihood of ureteral stone (positive predictive value 88%) 4
• CT hydronephrosis has 88% sensitivity and 85% specificity for predicting ureteric and obstructing renal pelvic calculi 4
• The combination of no hydronephrosis AND no hematuria has a 96.4% negative predictive value for ureteral stone 4

Role of Contrast-Enhanced CT

• Avoid routine contrast-enhanced CT as initial imaging in suspected urolithiasis, as it provides limited added utility and can obscure stones within the renal collecting system 1, 5
• In a study of 322 patients, follow-up contrast-enhanced CT after initial non-contrast CT changed management in only 1.9% of cases 5
• Consider contrast-enhanced CT only when: (1) non-contrast CT is negative for stones AND clinical suspicion for alternative diagnosis is high, or (2) patient has negative urinalysis without history of urolithiasis 1, 5
• Contrast-enhanced CT detected clinically significant alternative diagnoses (renal infarct, splenic infarct, pyelonephritis, acute appendicitis) in only 1.2% of patients where non-contrast CT was completely normal 5

Common Pitfalls to Avoid

• Do not assume absence of fever and dysuria rules out urinary pathology - urolithiasis frequently presents without these symptoms 2, 3
• Recent contrast administration can affect collecting system density and complicate interpretation 4
• Hydronephrosis may develop in a delayed fashion, leading to false-negative early ultrasound findings 1
• Low-dose CT protocols are sufficient for determining stone size and location for surgical planning when moderate to severe hydronephrosis is already documented 4, 1

Alternative Diagnoses to Consider

Non-contrast CT effectively identifies non-urolithiasis causes of flank pain in over 30% of patients, including gastrointestinal, vascular, gynecologic, and other genitourinary pathologies 3, 6