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Invited Commentary |
1 Mallinckrodt Institute of Radiology, Washington University School of Medicine, St Louis Children's Hospital, Missouri
Fernbach et al , all of whom are experienced in performing voiding cystourethrography in children, have produced an excellent "how we do it" article. Their technique involves minor variations on the technique used by other pediatric radiologists. As with most procedures in radiology, however, there is no right or wrong way to perform voiding cystourethrography. Perhaps the greatest controversy surrounding this procedure involves something the authors did not write about—but I will address that later.
It is important to be aware of the results of prior urinary tract imaging before starting voiding cystourethrography. Ultrasonography (US) of the kidney or bladder is usually performed prior to voiding cystourethrography, and the US findings (eg, ureteroceles, posterior urethral valves, vesicoureteral reflux) will affect the technique used.
Should sterile urine be documented in the 48-hour period before voiding cystourethrography is performed? That is a question for which I have no definitive answer. It is my practice to proceed with the study if the upper tracts appear normal at US, there are no signs or symptoms of urinary tract infection, and the patient is over 2 years old. I monitor the bladder filling phase to avoid gross vesicoureteral reflux. If there is moderate or severe pyelocaliceal and ureteral dilation at US suggesting vesicoureteral reflux, or if the patient is an infant, I will either have the urine examined prior to starting voiding cystourethrography or reschedule the study.
How long should one wait after the start of antibiotic therapy before performing voiding cystourethrography, and does the presence of a urinary tract infection increase the prevalence of vesicoureteral reflux? A period of 2–3 days is sufficient to sterilize the urine. In a study by Garin et al (1), the prevalence of vesicoureteral reflux in patients with symptomatic urinary tract infections was the same with 2–3 days of treatment prior to voiding cystourethrography as with a 6-week delay.
On occasion, parents and physicians will insist that the child be sedated with drugs such as midazolam before undergoing voiding cystourethrography. Although I have come to accept the use of sedation, its impact on the depiction of vesicoureteral reflux is unclear.
If the upper tracts are appreciably dilated at preliminary US, I tend to keep the bottle of contrast material (17.2% iothalamate meglumine [Cysto-Conray; Mallinckrodt, St Louis, Mo]) within about 1 foot (~30 cm) of the table to generate less intravesical pressure. Having witnessed death due to sepsis in two infants who underwent voiding cystourethrography and marked renal atrophy in another, I monitor bladder filling carefully to avoid overdistending the upper tracts and causing intrarenal vesicoureteral reflux (2). Although voiding cystourethrography in the pediatric population has a low prevalence of complications (3), one should weigh the relative risks and benefits of each study.
I perform fluoroscopy more frequently during bladder filling than do Fernbach et al and document the volume at which vesicoureteral reflux occurs. In addition to routine scout digital images of the abdomen, I also obtain a lateral digital image of the pelvis (including the sacrum) during bladder filling in children with a history of voiding dysfunction to exclude masses and spinal abnormalities.
I have not found bladder capacity calculations to be useful for voiding cystourethrography (4) because there is so much variation among children with respect to bladder volume and emptying. A bladder that fills quickly tends to hold less contrast material than one that fills more slowly, and infants frequently have multiple voids.
In girls, I observe the act of voiding with fluoroscopy to determine if the voiding is intermittent or if there are changes that suggest bladder dyssynergy with dilation of the proximal urethra, although urethral appearance is most closely related to urinary flow rate. Bladder dyssynergy can often be suspected on the basis of the patient's voiding history. Like Fernbach et al, I usually leave the catheter in place while the patient begins to void but generally remove it during voiding.
In patients who are at high risk for reflux due to the presence of disease processes such as upper tract dilation or ureteroceles, I tend to use several cycles of voiding if no vesicoureteral reflux is seen on the first cycle. S. Jequier and J.C. Jequier (5) demonstrated vesicoureteral reflux in an additional 3% of patients with a second cycle of bladder filling and 4% with a third cycle. Paltiel et al (6) demonstrated an increased prevalence of vesicoureteral reflux with cyclic voiding.
If a girl cannot void, I will eventually abandon the effort, have her void in the toilet, and then quickly obtain an image to document any vesicoureteral reflux. With this technique, it is not likely that higher grades of vesicoureteral reflux will be missed.
Occasionally, transient hematuria occurs after voiding cystourethrography, and I usually tell the patient's family that transient hematuria or dysuria may occur secondary to the procedure.
Unlike with some other imaging studies, there is a very high level of agreement among experienced pediatric radiologists in the soft- and hard-copy interpretation of voiding cystourethrograms (7,8).
If vesicoureteral reflux is thought to be clinically indicated in an older girl, it may be more appropriate from a radiation exposure standpoint to perform radionuclide cystography than voiding cystourethrography, although Kleinman et al (9) have described a tailored low-dose fluoroscopic technique as an alternative to radionuclide cystography.
Another technique that can be used to reduce radiation exposure is pulsed fluoroscopy (10). Exposure associated with different fluoroscopy units varies considerably. In addition, when planning equipment replacement it is prudent to consider purchasing equipment that allows low-dose fluoroscopy.
US cystography can be used to detect vesicoureteral reflux without use of radiation. Microbubble techniques are especially useful because microbubbles make vesicoureteral reflux in the ureter and kidney much easier to identify (11). US cystography does not allow optimal visualization of the urethra, although posterior urethral valves have been diagnosed with US. US cystography and voiding cystourethrography have reasonably good correlation, although the data are limited (11). US can be used to visualize the kidneys as well as to detect reflux.
Fernbach et al's recommendation that antibiotic therapy be started immediately after the demonstration of vesicoureteral reflux may seem reasonable, but the current literature does not support such urgency. Furthermore, their assertion that 20% of vesicoureteral reflux will be missed if no voiding occurs requires documentation. I have seen vesicoureteral reflux resolve in patients with a periureteral diverticulum; therefore, the authors' statement that it does not resolve is not always true.
Some of our most cherished beliefs about vesicoureteral reflux, urinary tract infections, and reflux nephropathy are not supported by well-designed, prospective, multicentered studies, which could profoundly alter our current understanding and management of these disease processes and affect the frequency with which voiding cystourethrography is performed. The prevalence of vesicoureteral reflux in children without urinary tract infection appears to be significantly higher than earlier estimates and approaches that seen in children with urinary tract infection (12). The prevalence of vesicoureteral reflux in asymptomatic siblings of children with vesicoureteral reflux and in girls with asymptomatic bacteriuria is similar to that in children with urinary tract infection (12). Urinary tract infections affecting the bladder do not cause vesicoureteral reflux (13). Vesicoureteral reflux does not predispose to urinary tract infection or pyelonephritis, nor does it predispose to renal scarring in patients with acute pyelonephritis (1). Urinary tract infection is independent of the presence of vesicoureteral reflux (12). Severe vesicoureteral reflux is most commonly seen in male infants with renal damage including renal failure but with no history of urinary tract infection (14–16). The small bladders in these infants have urodynamic abnormalities with high voiding pressures. Sterile vesicoureteral reflux in the absence of elevated voiding pressures or bladder dysfunction does not produce renal damage (including scars) (17). Renal growth rates are unaffected by the initial severity or the persistence of vesicoureteral reflux, and no new renal scars develop after puberty (18). Asymptomatic bacteriuria and vesicoureteral reflux are not associated with renal scars (19). In patients with vesicoureteral reflux, renal scar development may be no different in those undergoing continuous antibiotic prophylaxis than in those undergoing treatment for discrete episodes of urinary tract infection (20). Many children with renal cortical defects at dimercaptosuccinic acid scintigraphy do not demonstrate vesicoureteral reflux, and most patients with vesicoureteral reflux do not demonstrate renal defects at scintigraphy (21). The natural history of the resolution of asymptomatic vesicoureteral reflux is the same as that of symptomatic vesicoureteral reflux (22). Spontaneous resolution of vesicoureteral reflux is likely in siblings of children with vesicoureteral reflux (23). In a study of animals with experimentally produced vesicoureteral reflux in utero, alterations in renal function occurred when bladder dynamics were altered, and vesicoureteral reflux resolved with normalization of bladder urodynamics (24).
Urinary tract infections per se do not cause end-stage kidney disease (25). The frequency of breakthrough infections, renal function, renal growth, and development of new or progressive scarring is the same for medical and surgical treatment of reflux (26). There is no evidence that renal defects commonly seen at dimercaptosuccinic acid scintigraphy in patients with urinary tract infection will necessarily result in end-stage renal disease (27).
Fernbach et al beautifully summarize voiding cystourethrography in the pediatric patient. The question of which patients should undergo this procedure is increasingly controversial. It is likely that the frequency of its use will change as our understanding of urinary tract infections in infants and children, renal scarring (including reflux nephropathy), and vesicoureteral reflux evolves.
References
Department of Radiology, Evanston Hospital, Evanston, Illinois; Department of Radiology, Rush-Presbyterian-St Luke's Medical Center, Chicago Illinois; Department of Radiology, Children's Memorial Hospital, Chicago, Illinois
We wish to thank Dr McAlister for sharing his experiences, thoughts, and techniques. Readers should also find the additional references most helpful.
Related Article
RadioGraphics 2000 20: 155-168.
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