What is the best course of action for a male in his 50s with persistent flank pain for over a month and a negative urine culture?

Immediate Imaging with Non-Contrast CT is Essential

A male in his 50s with persistent flank pain for over a month and negative urine culture requires non-contrast CT of the abdomen and pelvis as the definitive diagnostic test, as this has 98-100% sensitivity and specificity for detecting urinary stones and identifies alternative diagnoses in approximately one-third of patients. 1, 2

Why CT is Critical in This Case

The negative urine culture does not rule out urolithiasis or other serious pathology. The duration of symptoms (over one month) makes this particularly concerning and demands definitive imaging rather than observation. 1

• Non-contrast CT abdomen/pelvis is the gold standard with near-perfect accuracy for detecting stones regardless of size, location, or chemical composition 2, 3
• This modality will identify extraurinary causes in about one-third of patients presenting with flank pain, which is crucial given the atypical presentation with prolonged symptoms 1, 3
• The absence of infection (negative urine culture) does not exclude obstructive uropathy, malignancy, or other serious conditions 4, 5

Key Diagnostic Considerations Beyond Stones

Musculoskeletal vs. Renal Origin

• Pain that worsens after prolonged static positioning or with external pressure suggests musculoskeletal origin involving paraspinal muscles or facet joints 1, 6
• Classic renal colic presents as colicky, wave-like severe pain independent of body position, radiating to the groin or genitals with abrupt onset 1
• The chronic nature (>1 month) makes typical acute stone disease less likely and raises concern for alternative diagnoses 1

Critical Alternative Diagnoses to Consider

• Renal cell carcinoma can present with flank pain and should be a diagnostic concern in this age group 5
• Page kidney (subcapsular hematoma causing compression) can present with flank pain and hematuria, mimicking nephrolithiasis 4
• Right-sided pain may indicate colonic diverticulitis, inflammatory bowel disease, or gastroenteritis 1
• Vascular pathology including renal artery stenosis or aneurysm must be excluded 4

Algorithmic Approach

Step 1: Obtain Non-Contrast CT Abdomen/Pelvis Immediately

• Do not delay imaging based on negative urine culture 1, 2
• This single test provides comprehensive evaluation of urinary and extraurinary causes 3, 7

Step 2: Interpret Results and Direct Management

If stones <5 mm identified:

• Typically pass spontaneously with conservative management 1
• Provide NSAIDs for analgesia and instruct patient to maintain high fluid intake 1
• Arrange urology follow-up within 7-14 days 1

If stones >5 mm or complete obstruction:

• Urgent urology referral for potential endoscopic intervention 1
• These require active management rather than expectant approach 1

If no stones but alternative diagnosis found:

• 41% of these patients require hospitalization and 22% need surgical intervention, compared to only 14% and 4% respectively when no CT diagnosis is made 1
• Direct management based on specific findings (malignancy, inflammatory process, vascular pathology) 3, 7

If CT is negative:

• Consider musculoskeletal evaluation with focus on lumbar spine pathology 1, 6
• Reassess for positional nature of pain and response to musculoskeletal interventions 6

Red Flags Requiring Urgent Evaluation

• Fever, chills, or signs of systemic infection (suggests pyelonephritis or perinephric abscess despite negative culture) 1, 6
• Inability to urinate or decreased urine output (suggests complete obstruction) 1, 6
• Hemodynamic instability (consider ruptured abdominal aortic aneurysm in this age group) 6
• Visible hematuria (shifts probability toward structural pathology including malignancy) 1, 5

Common Pitfalls to Avoid

• Do not assume negative urine culture excludes serious pathology - stones, malignancy, and vascular causes may present without infection 4, 5
• Do not rely on plain radiography (KUB) - only 72% sensitive for large stones and 29% sensitive overall 1
• Do not use contrast-enhanced CT initially - contrast can obscure stones within the collecting system 2
• Do not dismiss chronic symptoms as musculoskeletal without imaging - the one-month duration demands exclusion of structural pathology 5

Alternative Imaging Only If CT Contraindicated

Ultrasound may be considered if radiation concerns exist, but has significantly lower sensitivity (45% vs. 98-100% for CT) and frequently misses stones and alternative diagnoses 6, 3. Given the patient's age, gender, and chronic symptoms, the diagnostic yield of CT far outweighs radiation concerns. 2, 8