Potential role of colour-Doppler cystosonography with echocontrast in the screening and follow-up of vesicoureteral reflux

Role of Contrast-Enhanced Voiding Urosonography in the Evaluation of Renal Transplant Reflux - Comparison with Voiding Cystourethrography and a New Classification

Vesicoureteral reflux (VUR) is a common urological complication in renal transplant patients.

THE AIM

of this study is to evaluate the performance of contrast-enhanced voiding urosonography (CEvUS) in the diagnosis and classification of reflux into the renal allograft, to evaluate and classify VUR into the allograft using voiding cystourethrography (VCUG) and CEvUS, to compare the two methods, and to propose a new classification of reflux into the allograft based on CEvUS and VCUG assessment, in line with the international reflux grading system.

MATERIALS AND METHODS

 From January 2017 to July 2019, 84 kidney transplant patients were enrolled. All patients underwent VCUG and CEvUS.

RESULTS

 In 76 cases there was agreement between VCUG and CEvUS (90 %) (Kappa = 0.7). The sensitivity of CEvUS using VCUG as the gold standard was 90 %, and the specificity was 92 %. Of the 7 cases diagnosed by VCUG and not by CEvUS, 6 were grade 1 and 1 was grade 2.

CONCLUSION

 Transplant patients with reflux symptoms should undergo CEvUS. If the outcome is negative, VCUG should be performed. The classification that we propose is better suited to describe VUR in transplant patients, because it is simpler and takes into account whether reflux occurs not only during urination but also when the bladder is relaxed.

Voiding urosonography with ultrasound contrast agents for the diagnosis of vesicoureteric reflux in children. I. Procedure

Voiding urosonography (VUS) encompasses examination of the urinary tract with intravesical administration of US contrast agent (UCA) for diagnosis of vesicoureteric reflux (VUR). The real breakthrough for US examination of VUR came with the availability of stabilized UCAs in the mid-1990s. This article presents a comprehensive review of various procedural aspects of VUS. Different US modalities are available for detecting the echogenic microbubbles: fundamental mode, colour Doppler US, harmonic imaging and dedicated contrast imaging with multiple display options. The reflux is graded (1 to 5) in a similar manner to the system used in voiding cystourethrography (VCUG). The most commonly used UCA for VUS, Levovist, is galactose-based and contains air-filled microbubbles. The recommended concentration is 300 mg/ml at a dose of 5-10%, or less than 5%, of the bladder filling volume when using fundamental or harmonic imaging modes, respectively. There are preliminary reports of VUS using a second-generation UCA, SonoVue. Here the UCA volume is less than 1% of the bladder filling volume. There is no specific contraindication to intravesical administration of UCA. The safety profile of intravesical Levovist is very high with no reports of side effects over a decade of use in VUS.

Voiding urosonography with US contrast agents for the diagnosis of vesicoureteric reflux in children. II. Comparison with radiological examinations

Studies comparing voiding urosonography (VUS) with voiding cystourethrography (VCUG) and direct radionuclide cystography (DRNC) were analyzed and detailed tables demonstrating the diagnostic values and grading of vesicoureteric reflux (VUR) are presented. Comparative studies of DRNC were too few and did not allow definite conclusions. Using VCUG as the reference, the results of VUS were as follows: sensitivity 57-100%, specificity 85-100%, positive/negative predictive values 58-100%/87-100%, respectively, and diagnostic accuracy 78-96%. With the exception of two studies the diagnostic accuracy reported was 90% and above. In 19% of pelviureteric units (PUUs) the diagnosis was made only by VUS and in 10% only by VCUG. Thus in 9% of PUUs more refluxes were detected using VUS. In 73.6% the reflux grades were concordant in VUS and VCUG. Reflux grade was found to be higher with VUS than with VCUG in 19.6% of PUUs. In 71.2% of PUUs with grade I reflux on VCUG, the reflux was found to be grade II and higher on VUS. The common selection criteria for VUS as the primary examination for VUR currently include (a) follow-up studies, (b) first examination for VUR in girls, and (c) screening high-risk patients.

Imaging strategies for vesicoureteral reflux diagnosis

The prevalence of vesicoureteral reflux (VUR), although reported to be low in the general population, is high in children with urinary tract infection (UTI), first degree relatives of patients with known VUR and children with antenatal hydronephrosis. In addition, it has been shown that VUR and UTIs are associated with renal scarring, predisposing to serious long-term complications, i.e., hypertension, chronic renal insufficiency and complications of pregnancy. Therefore, diagnostic imaging for the detection of VUR in the high-risk groups of children has been a standard practice. However, none of these associations has been validated with controlled studies, and recently the value of identifying VUR after a symptomatic UTI has been questioned. In addition, several studies have shown that renal damage may occur in the absence of VUR. On the other hand, some patients, mainly males, may have primary renal damage, associated with high-grade VUR, without UTI. Recently, increasing skepticism has been noted concerning how and for whom it is important to investigate for VUR. It has been suggested that the absence of renal lesions after the first UTI in children may rule out VUR of clinical significance and reinforces the redundancy of invasive diagnostic techniques. Therefore, the priority of imaging strategies should focus on early identification of renal lesions to prevent further deterioration.

Cyclic contrast-enhanced harmonic voiding urosonography for the evaluation of reflux. Can we keep the cost of the examination low?

The purpose of this study was to evaluate whether a second cycle of contrast-enhanced voiding urosonography (VUS) with no added contrast medium (CM) can increase the detection rate of vesicoureteral reflux (VUR). One hundred twelve consecutive children with a mean age of 2.9 years with 224 kidney-ureter units (KUU) underwent two cycles of contrast-enhanced harmonic VUS. The first cycle of VUS was performed with 3.5-12.5 ml of suspension 300 mg/ml SH U 508 A and was followed immediately by a second cycle with only saline without adding CM. VUR was detected in 57 KUU from 44 children (39%) at the first cycle of VUS. Eight of the remaining 68 non-refluxing children (12%) demonstrated VUR at the second cycle (P=0.045). Most cases of missed reflux at the first cycle were grade II (75%). However, in two KUU from two children missed reflux was grade III. In one child reflux (grade II) was missed on the second cycle. Comparing the second cycle of VUS with the first cycle, concordant findings regarding the presence or absence as well as the grade of reflux were found in 94% of KUU. A second cycle of contrast-enhanced harmonic VUS with no added CM discloses significantly more cases of VUR at no additional cost for the examination.

Current status of vesicoureteral reflux diagnosis

In children, diagnostic imaging for vesicoureteral reflux (VUR) encompasses both radiologic and sonographic modalities. The former comprises voiding cystourethrography (VCUG), the most widespread method for examination for reflux, and radionuclide cystography (RNC). In RNC the radiation exposure is significantly less than in VCUG with continuous fluoroscopy, but the anatomic details depicted are much inferior. With the introduction of pulsed fluoroscopy, the radiation exposure of VCUG has been markedly curtailed. VCUG is the first imaging choice for the urethra. The sonographic diagnosis of VUR with the intravesical administration of an ultrasound (US) contrast agent-voiding urosonography (VUS)-is being used increasingly in the routine diagnostic imaging work-up of reflux. Various sonographic reflux examination methods had been tried in the past. The real breakthrough came with the availability of stabilized US contrast media. Further impetus came with the introduction of harmonic US imaging. The recent release of a second generation US contrast medium promises to make a further positive impact on VUS. The diagnostic accuracy of contrast-enhanced VUS has been found to be comparable to radiologic methods. VUS is primarily performed in follow-up studies and as the primary reflux examination modality in girls.

Harmonic US imaging of vesicoureteric reflux in children: usefulness of a second generation US contrast agent

BACKGROUND

Contrast-enhanced voiding urosonography (VUS) is largely accepted both for the diagnosis and follow-up of vesicoureteric reflux (VUR) in children.

OBJECTIVE

To evaluate the usefulness of contrast-enhanced second-harmonic VUS in the diagnosis and grading of VUR, using a second-generation contrast agent.

MATERIALS AND METHODS

Eighty consecutive children were prospectively studied with contrast-enhanced second-harmonic VUS. All children received a second-generation contrast medium, constituted by phospholipid-stabilized microbubbles of sulphur-hexafluoride (SonoVue, Bracco, Milan, Italy). US monitoring of the bladder, of the retrovesical space and of the kidneys was performed using, alternatively, both tissue-harmonic and contrast-harmonic modes. In those young boys where VUR was depicted at VUS, examination was completed with transperineal, sagittal urethral exploration during micturition. VUR was graded in five steps and diagnoses were compared with voiding cystourethrography (VCUG).

RESULTS

VUR was diagnosed in 52 reno-ureteral units with VUS. In 49 of these reno-ureteral units, VCUG confirmed the presence of VUR. In comparison to VUS, sensitivity and negative predictive value of VCUG were inferior. The grade of VUR detected at VUS was higher than that detected at VCUG in three units. In no case was the grade of VUR detected at VCUG higher than the one detected at VUS. The differences between VUS and VCUG in grading VUR were statistically significant (p=0.02). Imaging of the normal posterior urethra was skilfully demonstrated with US in 15 young boys with VUR. No statistically significant differences were found between tissue-harmonic and contrast-harmonic mode (p=0.102).

CONCLUSIONS

Contrast-enhanced second-harmonic VUS is a sensitive and easy technique for the evaluation of VUR. A second-generation US contrast medium such as SonoVue, if available, should be the first choice as the dose required for one examination is much lower and consequently significant reduction of contrast agent cost is possible.

Cyclic voiding urosonography in detecting vesicoureteral reflux in children

Three methods are currently used to identify vesicoureteral reflux (VUR) in children, namely X-ray voiding cystourethrography (VCUG), radionuclide voiding cystography (RVC), and, recently, echo-enhanced voiding urosonography (VUS). It is known that the sensitivity of VCUG and RVC for detecting VUR can be improved by using cyclic procedures, such as repeated bladder filling and voiding. The purpose of our prospective study was to evaluate whether the cyclic procedure is superior to the conventional (one cycle only) procedure in VUS also. VUS was performed in 49 patients, aged 1.4-15.8 years (mean 4.1 years). After the first micturition, the catheter was left in place and the whole procedure was repeated under the same conditions. The results of the first and second cycles and the combined procedure were compared. In the initial cycle, 7 of 35 (20%) refluxing renal units that were detected in the second cycle and 4 of 26 (15%) children with at least unilateral VUR were missed. Cyclic VUS detected 25% more VURs than the conventional (one cycle only) VUS ( P=0.049) and revealed 50% more VUR III than the first cycle. Our results suggest that cyclic VUS is superior to conventional VUS.

A review of nonconventional ultrasound techniques and contrast-enhanced ultrasonography of noncardiac canine disorders

Modern ultrasound contrast media are gas-containing stabilized microbubbles that remain intact in the circulating blood for several minutes after intravenous injection and increase the intensity of the backscattered ultrasound. When the microbubbles disappear from the blood, they can be detected in the parenchyma of the liver and the spleen for about 30 more minutes (late liver- and spleen-specific phase). The insonated microbubbles produce second harmonic ultrasound frequencies, whose detection requires nonconventional ultrasound modalities such as pulsed inversion imaging. Nonconventional ultrasound techniques can also be used without microbubbles because second harmonics can be generated by ultrasound in tissues as well. The physical principles and advantages of nonconventional ultrasound techniques are described. The circulating microbubbles can be used not only to enhance weak Doppler signals, but also to perform dynamic contrast studies. Contrast-enhanced dynamic ultrasound studies--similar to contrast-enhanced CT and MRI examinations--have been used in humans to characterize lesions noninvasively (i.e., without biopsies) found during conventional ultrasound examinations. To map the distribution of contrast medium in a nodule or in an organ, specific scanning techniques such as stimulated acoustic emission have been developed. Stimulated acoustic emission occurs when high acoustic pressure ultrasonic waves disrupt the stationary or slowly moving microbubbles. This results in the release of a large amount of harmonic ultrasound frequencies. When the stimulated acoustic emission technique is used for dynamic studies, scanning must be interrupted several times to allow the microvasculature of the lesion to refill with microbubbles (interval delay imaging). The contrast patterns of malignant and benign hepatic nodules in humans have been the most intensively studied. Another type of dynamic study in humans measures the transit time of the contrast medium; that is, how fast the peripherally injected microbubbles reach the hepatic veins. Hepatic cirrhosis can be differentiated from other diffuse parenchymal liver diseases by a shorter transit time. Introducing nonconventional ultrasound techniques and ultrasound contrast media in veterinary diagnostic imaging may have potential value; however, intensive research should be carried out before ultrasound contrast agents can routinely be used in clinical practice.

Simultaneous voiding cystourethrography and voiding urosonography

PURPOSE

To compare the diagnostic accuracy of contrast-enhanced voiding urosonography (VUS) and voiding cystourethrography (VCUG) during simultaneous performance of both examinations.

MATERIAL AND METHODS

A total of 24 children, 16 girls and 8 boys, with a mean age of 3.5 years referred for reflux examination were recruited for the study. After transurethral bladder catheterization, radiographic contrast medium, followed directly by the US contrast medium, were administered. Fluoroscopic VCUG and VUS were carried out concurrently in the same patient. When 1 kidney was scanned by ultrasound, fluoroscopy was performed on the contralateral side.

RESULTS

In 19 of the 47 kidney-ureter-units (KUU) vesicoureteral reflux (VUR) was detected. In 16 units the reflux was detected by both VCUG and VUS. In 3 KUUs the reflux was detected only at VCUG. All 3 cases were grade 1. Taking the VCUG as the reference standard, VUS had 84% sensitivity, 100% specificity, 100% and 90% positive and negative predictive values, respectively.

CONCLUSION

A dependable comparison could be achieved by performing VCUG and VUS at the same time and under the same conditions. It reconfirmed that VUS is reliable in the exclusion or verification of reflux.