A prospective diagnostic study conducted in Iran has identified specific ultrasonographic thresholds that may help clinicians distinguish true ureteropelvic junction obstruction (UPJO) from benign dilatation in children. The research, published in the African Journal of Urology, evaluated the diagnostic value of post-furosemide ultrasonography in 55 children with borderline pelvicalyceal dilatation, defined as a renal pelvis anteroposterior diameter (APD) between 10 and 20 mm. The study aimed to determine whether this non-invasive imaging technique could serve as a reliable alternative to diuretic renal scintigraphy (DRS), the current standard of care, particularly in settings where nuclear imaging is limited or inaccessible.

The study was conducted at Akbar Pediatric Hospital, a tertiary center affiliated with Mashhad University of Medical Sciences, between 2021 and 2024. The target population included children aged one month to 12 years who had suspected UPJO and no prior history of pyeloplasty. Patients were selected through consecutive non-probability sampling. Inclusion criteria required borderline APD on ultrasonography, while exclusion criteria covered anatomical anomalies such as horseshoe kidney, duplex systems, ectopic or solitary kidneys, and any contraindication to furosemide administration. Written informed consent was obtained from parents or legal guardians for all participants.

The diagnostic protocol involved a standardized ultrasound examination performed by a single senior pediatric radiologist with over a decade of experience. Measurements were taken using a Voluson E6 ultrasound system with a convex transducer. The APD of the renal pelvis was measured in the transverse plane at the level of the renal hilum, using inner-to-inner caliper placement. Following the baseline scan, each child received an intravenous injection of furosemide at a dose of 1 mg/kg. Repeat ultrasonography was performed at 18 and 30 minutes post-injection to assess dynamic changes in APD and the intrarenal resistive index (RI). All patients subsequently underwent diuretic renal scintigraphy using a gamma camera, which served as the reference standard for diagnosis.

DRS was performed after the intravenous administration of 2.5 mCi of Tc-99m-EC. Furosemide was administered 10 minutes after radiotracer injection, and image acquisition continued for an additional 20 minutes. The interpretation of DRS was blinded to the ultrasound findings and relied on standard pediatric nuclear medicine criteria, including delayed post-diuretic drainage with a half-time greater than 20 minutes and persistent radiotracer retention. The decision to perform pyeloplasty was based on a combination of scintigraphic and clinical criteria, including significant functional deterioration and obstructive drainage patterns.

Among the 55 participants, the mean age was 3.40 years and the mean weight was 14.45 kg. The cohort consisted of 34 males and 21 females, with left kidney involvement being more frequent than right side involvement. Based on the DRS results, definitive UPJO was diagnosed in 51 children, representing 92.7% of the cohort. Six patients, or 10.9% of the total, required surgical intervention. No clinically significant hypotension or hemodynamic instability was observed in any participant following furosemide administration, suggesting the safety of the protocol in this pediatric population.

The study found that children diagnosed with UPJO had significantly higher APD and RI values at all post-furosemide intervals compared to those without UPJO. ROC curve analysis revealed that an APD of 11.5 mm or greater at 30 minutes post-injection demonstrated high diagnostic accuracy for UPJO, with an area under the curve (AUC) of 0.951. This threshold provided a sensitivity of 98.0% and a specificity of 75.0%. Additionally, a percentage increase in RI greater than 0.735 at 30 minutes showed the highest accuracy among RI-based indices, with an AUC of 0.975, a sensitivity of 96.1%, and a specificity of 100%.

Regarding the prediction of surgical need, the analysis identified an APD of 29.5 mm or greater at 30 minutes post-furosemide as a strong predictor for pyeloplasty. This threshold yielded a sensitivity of 83.3% and a specificity of 95.9%. Patients who underwent surgery had significantly higher APD measurements before and after furosemide injection compared to those managed conservatively. The percentage changes in APD at both 18 and 30 minutes were also significantly greater among patients requiring surgical intervention, indicating that the dynamic response to diuretic challenge is a key differentiator.

The researchers noted that the 30-minute protocol showed similar diagnostic power to previous studies that relied on measurements at 60 minutes, potentially making the test more feasible in busy clinical settings or with young children who may have difficulty waiting for extended periods. The dynamic measurement of RI after furosemide added value over static RI values, as perfusion changes may be easier to detect before surgical intervention. This approach offers a radiation-free, cost-effective alternative to DRS, which is particularly relevant in resource-limited settings where nuclear imaging is not readily available.

The study acknowledges several limitations, including the relatively small sample size and the single-center design, which may limit the generalizability of the findings. The very small number of non-UPJO cases in the cohort limits the precision of between-group comparisons, although appropriate non-parametric tests were applied. Additionally, while no significant hemodynamic instability was observed, transient changes in renal perfusion could theoretically influence APD and RI measurements. The short follow-up period may have missed late outcomes in non-operated cases, and the lack of a strictly quantified fluid-intake protocol introduces some residual variability related to hydration status.

Despite these limitations, the study highlights the potential of post-furosemide ultrasonography as a practical tool for guiding management decisions in children with borderline hydronephrosis. The identified cut-off values for APD and RI provide objective criteria that can support both the diagnosis and exclusion of UPJO. The authors suggest that further multicenter studies with larger samples and longer follow-up periods are warranted to validate these thresholds. They also propose that combining ultrasound data with artificial intelligence could improve diagnostic accuracy and reduce operator dependence in future clinical applications.

The study was designed to address a specific diagnostic gap in pediatric urology, where borderline pelvicalyceal dilatation often presents a clinical challenge. In many cases, it is difficult to determine whether the observed dilatation is harmless or indicative of an obstruction requiring surgical intervention. While diuretic renal scintigraphy is the current standard for this assessment, its accessibility is limited in various settings, including parts of Iran. Ultrasonography, by contrast, is widely available, affordable, and free of radiation, making it an appealing tool if it can provide reliable information about obstruction. The researchers aimed to evaluate whether post-furosemide ultrasonography could serve as a practical alternative to DRS, particularly for children with an anteroposterior diameter in the grey zone where decisions about pyeloplasty are not always clear.

The diagnostic protocol relied on dynamic changes in renal parameters following diuretic administration. Furosemide, a loop diuretic, inhibits the NKCC2 cotransporter in the thick ascending limb of Henle’s loop, thereby increasing natriuresis and diuresis. The onset of diuresis following intravenous furosemide is typically within five minutes, with peak effect reached by approximately 30 minutes in older children and adults. In neonates and infants, the plasma half-life may be substantially prolonged, sometimes to six hours or longer, due to immature renal clearance. Because the ultrasound measurements were taken at fixed time-points of 18 and 30 minutes post-furosemide, any transient changes in perfusion or intrarenal dynamics at these times might theoretically influence the anteroposterior diameter or resistive index readings. However, the study observed no clinically significant hypotension or hemodynamic instability in the cohort, suggesting that the actual impact of these transient changes was likely minimal.

The findings align with previous research while offering practical advantages in terms of timing and methodology. Earlier studies, such as those by Kazlauskas et al., relied on anteroposterior diameter measurements at 60 minutes, whereas the 30-minute protocol in this study showed similar diagnostic power. This shorter timeframe could make the test more feasible in busy clinics or with young children who may have difficulty waiting for extended periods. Additionally, while some prior work found that static resistive index values were not helpful, the dynamic measurement of RI after furosemide administration in this study clearly added value. This may be because perfusion changes are easier to detect before surgical intervention than after. The approach also differs from methods that use positional changes, such as the prone-supine decrease in APD, by using a standardized pharmacologic protocol without positional maneuvers, which may be easier to implement in some settings.

The low rate of pyeloplasty in this cohort, with only six patients requiring surgery, reflects the restricted inclusion of children with borderline pelvicalyceal dilatation. Most surgical series include moderate-to-severe hydronephrosis, which may not be representative of this specific population. Although the DRS criteria followed pediatric standards, diuretic renography may overestimate obstruction in children with large compliant pelves, reduced peristalsis, borderline renal function, or suboptimal hydration. This could partly explain why more patients met DRS criteria for UPJO than ultimately required surgery. The researchers noted that the consistent message from earlier work is that pelvis size after a challenge, whether physiologic or pharmacologic, is more informative than size alone. What this study adds is a faster, simpler method that provides accurate thresholds for both diagnosis and treatment planning.

The feasibility of applying this post-diuretic ultrasound protocol may vary across centers depending on staffing and workflow. However, the primary motivation was to evaluate a radiation-free, widely accessible, and cost-effective diagnostic option that could complement or serve as an alternative to DRS. In settings where nuclear imaging is costly or unavailable, this ultrasound-based approach may serve as a useful alternative. The study’s prospective design, standardized imaging protocol, and direct comparison with DRS and surgical outcomes help support the validity of the findings. Future research should include multicenter studies with larger samples and longer follow-up to validate these cut-off values. It would also be useful to test whether combining ultrasound data with artificial intelligence can improve diagnostic accuracy and reduce operator dependence in future clinical applications.

Subject of Research: Diagnostic accuracy of post-furosemide ultrasonography for ureteropelvic junction obstruction in children

Article Title: Diagnostic value of post-furosemide ultrasonography in children with pelvicalyceal dilatation (renal pelvis APD 10–20 mm): a predictor of pyeloplasty indication and comparison with diuretic renal scintigraphy

Article References: Masoud, M. R., Abbasioun, R., Seyed Ali, A., Elham, B., Hoseyn, N., & Atiyeh, N. (2026). Diagnostic value of post-furosemide ultrasonography in children with pelvicalyceal dilatation (renal pelvis APD 10–20 mm): a predictor of pyeloplasty indication and comparison with diuretic renal scintigraphy. African Journal of Urology, 32(1), Article 51. https://doi.org/10.1186/s12301-026-00600-7

Image Credits: AI Generated

DOI: 10.1186/s12301-026-00600-7

Keywords: pediatric urology, ultrasonography, furosemide, hydronephrosis, pyeloplasty, diagnostic imaging, renal obstruction, clinical diagnostics, Diagnostic, value, post-furosemide, children