Contrast media viscosity and its potential effect on the diagnosis of vesicoureteral reflux in children

Objective

To confirm that contrast-enhanced voiding cystourosonography (ceVUS) diagnoses more vesicoureteral reflux (VUR) than voiding cystourethrography (VCUG) and assess whether this could be explained by contrast agent viscosity differences.

Materials and methods

Children addressed for a VCUG for suspected or known VUR between April 2021 and June 2023 were prospectively included. CeVUS and VCUG were consecutively performed during the same procedure by two operators; for each pelviureteric unit (PUU), VUR presence was assessed and scored (I–V scale). At least 6 months later, three radiologists reassessed VUR grading on all ceVUS static images. The viscosity of the two contrast agents and of the urine were measured at 25 °C and 37 °C. Wilcoxon tests were used for comparisons and linear Cohen’s Kappa coefficient for Interobserver and Intraobserver agreement.

Results

Eighty-nine children, representing 192 PUU, were included. VUR was detected in 54 PUUs by at least one technique, by both in 30/54, by ceVUS only in 21/54 (38.8%), and by VCUG only in 3/54 (5.5%). VUR grade was higher with ceVUS in 19/30 (63.3%, p < 0.0008) PUUs. The ceVUS agent viscosity at 25 °C/37 °C (1.13 cP/1.03 cP) was almost identical to urine viscosity (1.14 cP/1.02 cP) and it was respectively 8 and 6 times lower than VCUG contrast agent viscosity (9.44 cP/6.03 cP). The Cohen’s kappa for ceVUS grading was between 0.75–0.97 (interobserver) and 0.93–0.98 (intraobserver).

Conclusion

Our study confirms that ceVUS detects more VUR and grades them higher in comparison to VCUG in children. This could be explained by the lower viscosity of the US contrast agent.

Key Points

Question Why are there differences in detecting and grading VUR between ceVUS and VCUG?

Finding VUR was detected by ceVUS or VCUG only in, respectively 38.8% and 5.5% of PUUs. VUR grade was higher with ceVUS in 63.3%.

Clinical relevance The higher detection rate and grading of vesicoureteral reflux in children by ceVUS might be explained by the lower viscosity of its sonographic contrast agent. CeVUS might reproduce the urine movement in the urinary tract.