| Abstract|| |
This study was undertaken to compare "direct" and "indirect" nuclear cystography for the detection of vesicoureteral reflux (VUR). Forty-five children (15 males and 30 females), ranging in age from 5 months to 10 years, were studied at the King Hussein Medical Center, Amman, Jordan between January 1998 and December 1999, using both direct (catheter) and indirect techniques of nuclear cystography (NC). Of the 82 ureters that could be compared, 32 ureters were positive for VUR on the direct technique while only 20 ureters showed VUR on the indirect technique (sensitivity 62%). Nine ureters, which did not show VUR on the direct cystogram, were read as positive on the indirect cystogram (specificity 82%). The false positive results of indirect nuclear cystogram make it invalid for VUR screening program, while the ease of assessment and low radiation dose from the direct NC has made this the recommended test for screening and follow-up of VUR.
Keywords: Nuclear cystography, Vesicoureteral reflux, Screening.
|How to cite this article:|
Khriesat I, Khriesat S, Hazza I. Comparison of "Direct" and "Indirect" Nuclear Cystography in the Diagnosis of Vesicoureteric Reflux. Saudi J Kidney Dis Transpl 2001;12:28-31
|How to cite this URL:|
Khriesat I, Khriesat S, Hazza I. Comparison of "Direct" and "Indirect" Nuclear Cystography in the Diagnosis of Vesicoureteric Reflux. Saudi J Kidney Dis Transpl [serial online] 2001 [cited 2021 Jan 18];12:28-31. Available from: https://www.sjkdt.org/text.asp?2001/12/1/28/33882
| Introduction|| |
Vesicoureteral reflux (VUR) in children is an important condition often associated with urinary tract infection and at times, renal scarring. Familial screening for VUR is justified due to a high percentage of siblings and offsprings of affected individuals, that are found to have reflux without symptoms. 
VUR has now been recognized to be hereditary and familial.  The incidence of VUR in siblings of affected individuals was shown to be significant, reported in 34 to 46% of siblings of whom, 75% were asymptomatic. , The risk of VUR in offsprings of known reflux patients was also found to be high with incidence rates reaching up to 65%. 
The diagnosis of VUR has been made traditionally by micturating cystourethrography (MCU) and radionuclide cystography; the latter test delivers less radiation dose to the patient. Winter first introduced catheter (direct) nuclear cystography (NC) in 1959,  and since then, the technique has become widely adopted, mainly in North America. , Many European centers however, have preferred to avoid catheterization and use the indirect technique. ,
In order to reduce the radiation dose delivered to the patient during VUR screening, and to recommend a reliable screening protocol, we conducted a study to compare the utility, sensitivity and specificity of both the direct and indirect methods.
| Patients and Methods|| |
Forty-five children, 15 boys and 30 girls ranging in age from five months to 10 years, including eight patients who were less than five years of age, were included in this study. All patients were seen at the King Hussein Medical Center, Amman, Jordan between January 1998 and December 1999, for renal assessment as part of the follow-up of VUR, or for evaluation of urinary tract infection (UTI). The medical records of all study patients were reviewed to determine previous X-ray examination results. The radionuclide renal scanning was analyzed to assess relative and absolute glomerular filtration rate (GFR) for each kidney. X-ray MCU had been previously performed in all patients and studied in the department of radiology using a fixed protocol with limited fluoroscopy and 110 mm-camera film. No attempt was made to re-X-ray the children with VUR at the time of the nuclear medicine assessment. Consent for urethral catheterization and direct as well as indirect NC was obtained from parents. The time gap between the direct and indirect techniques ranged from 18 to 48 hours with a mean of 30.4 hours.
| Nuclear Scanning Protocol|| |
Catheterization and voiding direct cystogram were carried out in essentially the same manner as that described by Willi and Treves.  Sterile infant-feeding tubes were used in most children. Voiding was allowed for all co-operative children in the up-right sitting position. They were viewed posteriorly with a restrainer belt across the chest and around the gamma camera. A bolus of 99m technetium (TC) sulfur colloid (37MBq) was then injected into the tubing at the commencement of bladder filling. Analog and digital acquisition was in 15second frames in 64 x 64 (word mode) matrix for 14 frames, followed by a 30second analog image when the bladder was full before catheter removal and voiding. Sixty, 5-second voiding frames were then collected and a 30-second post-void analog image was obtained.
Analysis of the direct cystogram was by inspection of the analog images and computer processed digital images. When reflux occurred to the upper ureter this was scored as positive for VUR. Grading of reflux and assessment of morphology of the bladder and urethra were not attempted.
Indirect cystogram was performed when 80% of the intravenously administered 99m TC DTPA for the renal study was in the bladder, and the child expressed a strong desire to void. The study was then identical to that of the direct cystogram after the "filling phase". Analysis was performed by inspection of the analog images and time-activity curves from regions including each kidney and upper ureter as described by Willi and Treves  for their analysis of direct cystogram.
Equivocal studies were re-analyzed using summed pairs of voiding frames. The indirect cytogram playback loops were read by two observers unaware of the patient's identity and a score for each ureter as positive or negative for VUR was given. The period between X-ray and nuclear medicine assessment varied from 2 to 12 months. The conditions for voiding were similar between the direct and the indirect cystogram techniques.
| Results|| |
Successful direct nuclear cystograms were obtained on all 45 patients, ranging in age from five months to 10 years. Twenty-five patients (32 ureters) showed reflux during voiding and/or filling of the bladder. No difficulties were encountered with the use of infant-feeding tubes; three male patients complained of dysuria after catheterization using balloon catheter. All ureters that showed VUR on direct cystogram had at some time shown VUR on X-ray MCU, or demonstrated scarred kidneys.
Forty-one patients had successful indirect cystogram performed. Four patients aged less than two years were unable to void within 15 minutes of initiating the study. Thus, only 82 ureters were available for comparison. Twenty ureters proved to be positive for VUR on indirect cystogram. Taking the direct cystogram as the standard, the indirect study read abnormal in only 20 of 32 "true-positive" cases (62% sensitivity). Also, the test was negative for VUR in only 41 of the 50 "true-negative" cases with nine false positive results (82% specificity).
| Discussion|| |
With the advent of new imaging techniques for the diagnosis of VUR in children, pediatricians have increasingly tried to limit the use of invasive procedures or those involving radiation, for the evaluation of a condition in which the outcome in the majority was thought to be benign.  However, a 5-year follow-up study has shown that even mild to moderate VUR, could be associated with renal injury.  Thus, early and definitive diagnosis of VUR has become important.
There remains an uncertainty about the most appropriate means of diagnosing VUR while protecting the child from radiation. Ultrasonography, despite its attraction as a non-invasive technique without radiation, still has a questionable place in the screening of VUR.  It has a high false negative rate and is not generally adequate for the detection of VUR in children. , As yet, no single non-invasive imaging technique is available to ascertain the diagnosis of VUR. The MCU still provides the most comprehensive assessment of VUR, allowing grading of the severity of reflux.  Many authors have recommended NC, , as it delivers a lower radiation exposure.  Follow-up studies of VUR have shown similar sensitivity rates for MCU and NC;  rather, another study has shown that NC has higher sensitivity than MCU, and was recommended for evaluation of VUR in adults as well as children.  On comparing "direct" and "indirect" NC, we found that a significantly less number of ureters were correctly shown to have VUR on indirect NC as compared to direct NC. Allowing for this true discordance of results between the two methods, we have come to regard the direct study as giving more information about the exclusion of reflux. The result is more easily appreciated by the clinician and no technical problems were encountered in the direct examination group. Moreover, while using the indirect NC, there were difficulties encountered during voiding at request in the younger patients. This further makes the direct technique the preferred one. Confidence in the results can help reduce the number of MCUs used in the follow-up and screening of children for VUR. The large numbers of children found to have positive indirect studies for VUR, without evidence of VUR by other tests, may well represent an unexpectedly high false positive rate for this technique. The clinical importance of direct NC to diagnose VUR was emphasizes by Nasralla et al,  which is compatible with our finding.
The same could not be said for most of the isolated "positive" indirect studies, which we feel, are most likely false positive results in these patients.
| Conclusion|| |
The ease of assessment and low radiation dose offered by direct NC have made this technique the recommended one for follow-up and screening of children for VUR. The indirect NC can only be valid for a relatively high VUR prevalence group, and may be quite inaccurate for a screening program.
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Department of Pediatrics, King Hussein Medical Center, P.O. Box 140440, Amman 11814