Most Appropriate Investigation: CT KUB (Non-Contrast CT)
For this adult male presenting with hematuria, right flank pain, and flank tenderness, CT KUB (non-contrast CT of kidneys, ureters, and bladder) is the most appropriate initial investigation, as it provides the highest diagnostic accuracy for both urolithiasis and alternative pathology that could explain his presentation. 1, 2
Rationale for CT KUB
Primary Diagnostic Considerations
Urolithiasis is the leading differential diagnosis given the combination of flank pain, flank tenderness, and hematuria in a male patient of this age group, even without prior stone history 1, 3
CT KUB has superior diagnostic performance with sensitivity and specificity both exceeding 90% for detecting urinary tract stones, far surpassing plain radiography (59% sensitivity) and ultrasound (75% for all stones, only 38% for ureteral stones) 4, 1
Absence of hematuria does not exclude stones: Up to 7% of patients with confirmed renal colic can have negative urinalysis for hematuria, so the presence of 20 RBCs strongly supports but is not required for stone disease 1
Critical Additional Benefits
Alternative pathology detection: CT KUB identifies clinically important alternative diagnoses in approximately 7% of patients presenting with suspected renal colic, including gastrointestinal emergencies, vascular pathology, and malignancies 5
The enlarged prostate finding raises concern for potential bladder outlet obstruction or malignancy, which CT can help evaluate by assessing for hydronephrosis and bladder abnormalities 2, 3
CT provides comprehensive anatomical information including stone size, location, degree of obstruction, and presence of hydronephrosis—all critical for management decisions 3, 6
Why Not the Other Options
Cystoscopy (Option A)
- Not appropriate as initial investigation for acute flank pain with hematuria 2
- Cystoscopy is indicated after imaging when bladder pathology is suspected or for complete hematuria workup in high-risk patients, but does not evaluate the upper urinary tract where this patient's symptoms localize 2, 7
- The enlarged prostate may warrant eventual cystoscopic evaluation, but only after ruling out acute upper tract pathology 2
Plain X-ray/KUB (Option C)
- Inadequate sensitivity (59%) for stone detection and provides no information about degree of obstruction, hydronephrosis, or soft tissue pathology 4, 8
- Cannot detect radiolucent stones (uric acid stones comprise 5-10% of all stones) 8
- Guideline evidence explicitly states radiography is not appropriate for initial evaluation of painful hematuria 4
- May be useful for follow-up of known radiopaque stones, but not for initial diagnosis 8, 6
Clinical Pearls
Right flank pain with tenderness localizes pathology to the upper urinary tract, making upper tract imaging essential rather than bladder-focused evaluation 1, 3
The combination of symptoms warrants urgent imaging to rule out obstructing stone, which can lead to renal damage if not promptly identified 6
Non-contrast CT is specifically preferred over contrast-enhanced CT for suspected urolithiasis, as contrast can obscure stone visualization 4, 3
If CT KUB is negative but clinical suspicion remains high, consider CT urography with contrast to evaluate for urothelial malignancy, especially given the patient's age range and enlarged prostate 2, 7