Contribution of simultaneous dynamic renal scintigraphy and serial ultrasonography to the diagnosis of urinary obstruction in children

Aim: The aim of this study is to evaluate the diagnostic effectiveness of dynamic ultrasonography (DUSG) in diagnosing obstructive hydronephrosis (HN) in patients undergoing dynamic renal scintigraphy (DRS) for unilateral hydronephrosis. Within this scope, dynamic ultrasonography data were compared with dynamic renal scintigraphy findings, and subsequently, these data were analyzed in comparison with clinical follow-up results to enable a more accurate diagnosis of obstruction. Patients and Methods: A total of 35 patients diagnosed with unilateral hydronephrosis, for whom a decision for DRS was made at the Istanbul University-Cerrahpaşa, Cerrahpaşa Medical Faculty Pediatric Nephro-Urology Council, between June 2022 and August 2024, were included in this study. Patient data, including gender, prenatal diagnosis, gestational week, age at presentation, and findings from ultrasound performed simultaneously with dynamic renal scintigraphy following a specific protocol, were prospectively collected. The findings of both methods were examined in detail and compared on a patient-by-patient basis. These data were then evaluated alongside the clinical outcomes of the patients. Results: Prenatal diagnosis was present in 30 (85%) of the 35 patients, with diagnoses made via USG. Thirty-three patients were born at term, while 2 (5.7%) were preterm (gestational age 30-32 weeks). The mean age at initial presentation was 33 months (0-132 months), and all patients were male. The HN was on the left side in 29 patients (82.8%) and on the right side in 6 patients (17.2%). Of the patients, 19 showed a diuretic response in dynamic renal scintigraphy, 10 had no response, and 6 had a partial response. In 4 patients, despite hydronephrosis findings on DUSG, drainage was observed on dynamic renal scintigraphy without the administration of a diuretic. In the remaining 31 patients, post-diuretic t½ values were examined. In the non-responsive group, t½ was > 20 minutes, while it was an average of 7.3 minutes (3-8 minutes) in the responsive group and 14.2 minutes (12-20 minutes) in the partially responsive group. In the assessment of dynamic ultrasonography findings, hydronephrosis persisted in USG 4 in 17 patients. For the remaining 18 patients, the anterior-posterior diameter of the renal pelvis (APDRP) returned to its USG 1 value or a lower value. Among the 17 patients whose APDRP had not returned to its USG 1 value by USG 4, 4 were partially responsive, and 6 were non-responsive to diuretic. Despite being diuretic-responsive, 7 patients had HN values in USG 4 that were higher than those in USG 1. Among the 18 patients whose HN returned to the initial value or a value lower than the initial in USG 4, 2 were partially responsive, and 4 were non-responsive to diuretic. A statistically significant change was observed in the percentage reduction between USG 3MM APDRP and USG 4MM APDRP in all patients. This emptying percentage was found to be 4.63% in the diuretic non-responsive group. In total, 20 patients were followed up conservatively, while 15 patients had an indication for intervention. Comparing these two groups, the APDRP in the follow-up group showed a significant increase on average in USG 3 but tended to return to the initial value by USG 4. In the group with intervention indications, a more significant increase was seen in USG 3, with partial retention of this increase by USG 4, indicating a more limited return. According to these results, there was a statistically significant difference between the two groups in terms of the USG 4% ratio (percentage emptying). Although DRS and DUSG data were graphically consistent, the timing was observed to differ. That is, the clearance of the radiopharmaceutical and the resolution of APDRP occurred at different times; t½ and HN ½ did not coincide. When DRS and DUSG data were evaluated together, a threshold value was identified that may aid in diagnosis. A significant portion (66.67%) of patients in the surgical group showed less than a 20% reduction in APDRP emptying percentage (USG 4%). In the group with an intervention indication, 6 patients had JJ stent insertion, 6 underwent pyeloplasty, and the remaining 3 were scheduled for surgical intervention. Among the findings in the patients with intervention indications, one patient with a JJ stent had hypoplastic UPJ, one had a filling defect in the UPJ, one had angulation in the UPJ, and the remaining 3 had narrow UPJs. Among the surgically treated patients, one had kinked UPJ leading to obstruction, one had aberrant vascular compression just distal to the UPJ with an invaginated appearance into the pelvis, and in the remaining 4 patients, the UPJ had a narrow lumen and fibrotic appearance. The clinical follow-up findings of all patients under observation were stable, with no deterioration observed in ultrasonography findings. In the latest follow-up ultrasounds of 13 patients (65%) in the follow-up group, the anterior-posterior diameter of the renal pelvis was found to be <10 mm. When comparing DRS and DUSG data with clinical outcomes, it was observed that the diagnosis of obstruction could be better understood when both methods were evaluated together. Conclusion: It was determined that the Lasix clearance curves in DRS were 68.5% consistent with the DUSG curves, although they did not match exactly. A temporal difference was observed between nuclear clearance and the regression of anatomical dilation. A threshold value of 20% for hydronephrosis (HN) regression in Doppler ultrasonography (DUSG) was found to be consistent in supporting obstruction. It was determined that a regression percentage of less than 20% in HN in DUSG, together with an obstructive pattern in DRS, had the highest predictive accuracy for clinical outcomes. In the group with an intervention indication, a significant negative correlation was found between half-life in DRS and HN regression percentage, indicating that as half-life increased, the HN regression percentage decreased, meaning patients with a longer half-life showed a lower reduction rate. In conclusion, it was determined that a more precise assessment could be made in the diagnosis of ureteropelvic junction obstruction (UPJO) when DUSG and DRS were evaluated together.