Superior Detection without Clinical Benefit: A Prospective Comparison of CT and Ultrasonography After Stone Surgery

To evaluate whether the superior diagnostic accuracy of non-contrast computed tomography (NCCT) translates into clinically meaningful changes in management compared with ultrasonography (US) during routine postoperative follow-up after endourological stone surgery.

In this prospective observational study (n=60), adult patients undergoing ureteroscopy (URS) or percutaneous nephrolithotomy (PCNL) were assessed at 4-6 weeks postoperatively using both US and NCCT within ≤72 hours. NCCT served as the reference standard. The primary outcome was the diagnostic performance of US. The secondary outcome was the proportion of cases in which NCCT findings led to a change in clinical management. Multivariable logistic regression was used to identify predictors of false-positive US findings.

Sixty patients were included (mean age 52.3 ± 18.6 years; mean BMI 26.2 ± 6.8 kg/m²). NCCT identified residual stones in 14 patients (23.4%), totaling 27 stones. On stone-based analysis, US demonstrated a sensitivity of 79% (95% CI 69-86%) and a positive predictive value of 75%. NCCT detected additional findings not visualized on US in 6 patients (10%), all of which were small (≤4 mm) and non-obstructive. Importantly, NCCT findings resulted in clinically meaningful changes in management in only 2 of 60 patients (3.3%), despite its higher diagnostic sensitivity. US demonstrated a tendency to overestimate stone size, particularly with increasing BMI, which was the only significant predictor of false-positive findings (OR 1.12 per kg/m², p = 0.008).

Although NCCT demonstrates superior diagnostic accuracy, it rarely results in clinically meaningful changes in management in routine postoperative follow-up after endourological stone surgery. Ultrasonography provides acceptable diagnostic performance for clinically relevant stones. These findings support a risk-adapted imaging strategy in which ultrasonography serves as first-line surveillance, reserving CT for cases where results are expected to influence management.