Contrast-enhanced ultrasound voiding cystography as a screening examination for vesicoureteral reflux in the follow-up of renal transplant recipients: a new approach

Background. The aim of the study was to evaluate a new diagnostic procedure, ultrasound contrast-enhanced voiding cystography (USVC), for vesicoureteral reflux (VUR) in renal transplant recipients and to compare it with radionuclide voiding cystography (RVC). Methods. Twenty-three renal transplant recipients with recurrent urinary tract infection were investigated simultaneously by RVC and USVC. After catheterization, the empty bladder was filled with normal saline (mean 250 +/- 30 ml) and 30-45 mBq of Tc-99m-labelled colloid. At the end of filling the bladder, 19.5 ml of galactose-based, microbubble-containing echo-enhancing agent, at a concentration of 200 mg/ml, was instilled. During the filling and voiding phases the movement of the radiotracer was recorded by a gamma camera and the presence of microbubbles in the urinary tract by ultrasound. RVC was used to detecte and grade the degree of VUR. Results. Nuclear studies identified VUR in 16 (69.6%) of 23 recipients with recurrent urinary tract infection: VUR grade I in three (13%) recipients, grade II in eight (34.8%) and grade III in five (21.7%) using a simplified grading system. USVC with contrast-enhancement detected VUR in 14 (60.9%) recipients. Overall sensitivity and specificity of contrast-enhanced USVC was 75 and 71%, respectively. Statistical analysis showed that the accuracy of this procedure increased with higher grades of VUR and its sensitivity reached 100% for detection of VUR grade III. Conclusion. In our preliminary study, contrast-enhanced USVC has proved to be an effective examination, with the same accuracy rate as RVC in detecting grade III VUR episodes with low diagnostic accuracy for low reflux grades.