The extraction factor: an estimate of single kidney function in children during routine radionuclide renography with 99mtechnetium diethylenetriaminepentaacetic acid

Primary non-refluxing megaureters

Megaureters may be primary or secondary, and the dilatation may be due to obstruction or reflux, or both or neither. The cause of primary obstructed megaureter is the aperistaltic and narrowed pre-vesical portion of the ureter. The inner sheath of the terminal ureter generally shows a reduced amount of longitudinal smooth muscle bundles and an increased amount of collagen. Primary non-refluxing megaureters represent 23% of all prenatal diagnoses of hydronephrosis. They are more common in males and on the left side, and in 25% are bilateral. In older children they may become symptomatic. The diagnostic work up should include an ultrasound, a micturating cystourethrogram and an isotopic renogram. Most primary megaureters regress spontaneously or remain stable without compromising renal function, but 10-25% require surgery because of a progressive reduction in renal function or increasing dilatation, or because they become symptomatic. The basic principles of surgical repair include: resection of the obstructing segment, reduction in size of the dilated ureter, and re-implantation into the bladder using an anti-reflux technique.

Neonatal hydronephrosis

With fetal abnormalities diagnosed during maternal ultrasound becoming more commonplace, the management of neonatal hydronephrosis has become one of the most interesting and controversial subjects in pediatric urology. Although it is recognized that obstruction must be treated, it is also clear that hydronephrosis may well exist without significant obstruction. Numerous experimental and clinical studies of the urinary tract have failed to lead to a clear consensus. Our approach consists of careful observation of patients with moderate hydronephrosis in well functioning kidneys. In patients with reduced function or a renal pelvic diameter of greater than 3 cm and dilated calyces, we lean more towards surgical intervention. Overall, an individualized approach is necessary.

Neonatal management. Role for early intervention

Although performing pyeloplasty on an infant with a relatively healthy kidney prior to the onset of renal damage is not as well-accepted as "aggressive observation," the authors argue that early intervention is the more "conservative" or safe method of treatment for infants with ureteropelvic junction (UPJ) obstruction. Using experimental and clinical data, the authors demonstrate that prolonged partial UPJ obstruction in the developing kidney causes significant renal morbidity with time.

Urinary tract obstruction in children

PURPOSE

Perinatal identification of children with congenital urinary obstruction has challenged our understanding of the pathophysiology and clinical treatment of many children with hydronephrosis.

MATERIALS AND METHODS

A critical review of recent reports relating to congenital urinary obstruction in children was performed in an attempt to integrate clinical and experimental information.

RESULTS

Several themes emerged from the many reports relating to congenital urinary obstruction that have not been previously emphasized. Congenital obstruction begins and evolves in a developing fetal kidney, indicating the importance of the effect of obstruction on renal growth and development, which is distinct from the postnatal renal response to obstruction. Variation in the ability of the developing kidney to compensate for obstruction may be an important factor in explaining variability in clinical and experimental reports. Clinical data show an unpredictable outcome of congenital hydronephrosis. Nonoperative management of hydronephrosis is supported by empirical evidence yet raises many questions regarding the certainty of outcome and the risks involved. It imposes on the practitioner a significant clinical obligation. The ability to differentiate between clinically significant and insignificant obstruction is the current challenge to be fulfilled by integrated clinical and experimental investigation.

CONCLUSIONS

The unique features of congenital urinary obstruction separate it from better understood acquired postnatal obstruction. Understanding the effects of obstruction on the developing kidney prenatally and postnatally is critical. A definition is proposed for congenital urinary obstruction in children, that is a condition of impaired urinary drainage which, if uncorrected, will limit the ultimate functional potential of a developing kidney.

Primary dilated megaureter: long-term followup

Previously, we reported on the changing concepts in the management of 35 neonates with primary obstructive megaureters, 25 of whom were observed without surgery for a mean of 28 months while 10 were surgically treated. We report the long-term outcome of the 25 patients who were managed without surgery. This group consists of 19 male and 6 female neonates with 19 unilateral and 6 bilateral dilated ureters. Of the patients 17 presented with an antenatal diagnosis of hydronephrosis, 2 with infection and 6 with incidental findings. None of the patients had vesicoureteral reflux. Followup serial imaging (2 or more studies per case) consisted of excretory urography in 18 of the 25 cases, diethylenetriaminepentaacetic acid renal scan in 16 and/or sonogram in 10. Mean followup was 7.3 years (range 4.8 to 12.4) for 24 patients and 1 was lost to followup after 1.5 years. Excretory urography showed improvement in urinary tract dilatation in 12 cases and stable dilatation in 6. Renal scans demonstrated expected interval increases in the glomerular filtration rate with age without any deterioration in per cent of renal function in all 16 cases. None of the patients had stones, pain or pyelonephritis. We conclude that it is safe to follow a select group of patients with primary dilated megaureters in the absence of vesicoureteral reflux. We recommend antibiotic prophylaxis and serial urinary tract imaging to confirm renal growth and preservation of renal function.

Ultrafast contrast enhanced magnetic resonance imaging of congenital hydronephrosis in a rat model

Since new ultrafast magnetic resonance imaging (MRI) might offer unique advantages for evaluating renal blood flow, anatomy and urinary excretion, we used this technique to characterize a rat model with congenital partial ureteropelvic junction obstruction. MRI of 9 rats from an inbred colony with unilateral congenital (nonsurgical) hydronephrosis was compared with the contralateral nonhydronephrotic kidney serving as control. Our new imaging technique consisted of a 1-minute ultrafast gradient recalled imaging sequence during the first minute (64 images per imaging time 960 milliseconds) after contrast bolus injection with gadolinium-diethylenetriaminepentaacetic acid for assessment of renal blood flow followed by a 30-minute period with image acquisition every 30 seconds to study contrast distribution and excretion. Signal intensities were analyzed continuously over selected, different regions of interest. Anatomic analysis of MRI noncontrast studies showed precise delineation of the hydronephrotic pelvis and corticomedullary junction. After contrast gadolinium-diethylenetriaminepentaacetic acid injection signal intensity from the region of interest from hydronephrotic kidneys differed from nonhydronephrotic kidneys by showing less cortical decrease, suggesting decreased blood flow, less medullary decrease and delayed contrast excretion. Clear contrast distribution among the cortex, medulla and collecting system allowed selective estimation of different regions of interest and excellent anatomic evaluation. Renal anatomy and renal pelvic pressures were confirmed after scans were completed. Ultrafast contrast enhanced MRI allows simultaneous assessment of renal morphology, blood flow and function. In hydronephrotic partially obstructed kidneys distinct flow and excretion patterns measured with contrast enhanced MRI allow differentiation between the obstructed and nonobstructed kidney on physiological rather than purely anatomic means. This imaging technique may provide a useful method of evaluating congenital hydronephrosis obviating the need for multiple different diagnostic procedures.

Does early pyeloplasty really avert loss of renal function? A retrospective review

We reviewed 75 cases of isolated, unilateral pediatric ureteropelvic junction obstruction and 167 diuretic radionuclide renograms performed during the last 8 years. Differential function of the affected kidney was calculated using scintillation count data at 1 and 3 minutes, and the area under the renogram curve between 1 and 3 minutes. There was no significant difference among the 3 measures of per cent differential function for a given patient. Per cent differential function on the first renogram preoperatively neither declined as age at presentation advanced nor did it vary according to the clinical presentation. Similarly, the changes in postoperative per cent differential function were unaffected by the age at initial presentation, manner of presentation, occurrence of postoperative complications or the surgeon. These data do not support the concept that pyeloplasty for the isolated, unilateral ureteropelvic junction obstruction should be performed early to avert loss of renal function.

Managing apparent ureteropelvic junction obstruction in the newborn

A total of 97 newborns with apparent ureteropelvic junction obstruction was evaluated from mid 1984 to 1989. Evaluation and management are described. Of these patients 39 with an affected kidney showing good initial differential function (greater than 35%) by diethylenetriaminepentaacetic acid scan and 2 showing diminished function (less than 35%) were followed nonoperatively. Six patients (15%) eventually required pyeloplasty for diminishing function (4), urinary tract infections (1) or symptoms of colic (1). The 4 patients with diminishing function improved after pyeloplasty to at least the initial level. A total of 12 patients with good initial function (greater than 35%) of the affected kidney underwent early pyeloplasty (within 6 weeks of diagnosis). They were compared to the similar group of patients managed nonoperatively and followed by sequential renal scans. Eventual changes in percentage differential function in the nonoperative and early surgery groups were +2.8% and +4.1%, respectively. Changes in extraction factor were +0.8% (nonoperative group) and +0.9% (surgery group). No statistically significant difference was found. In the kidney with apparent ureteropelvic junction obstruction and good function, an initial nonoperative approach with sequential renal scan followup and pyeloplasty as needed appears to be reasonable and has resulted in no permanent loss of function.

Monitoring renal function in children with urological abnormalities

In clinical practice glomerular filtration rate routinely is estimated by measuring serum creatinine and using the Schwartz formula for calculating an estimate of creatinine clearance or using the Gates formula for calculating the clearance of diethylenetriaminepentaacetic acid based on the uptake during radionuclide imaging. We compared these methods to the plasma clearance of iothalamate during extended constant infusion. All 3 tests were performed in 14 boys and 5 girls 9 months to 16 years old with urological abnormalities and moderate renal insufficiency. Using iothalamate as the reference, calculated creatinine clearance overestimated glomerular filtration rate by more than 20% in 12 of the 19 patients (63%). Diethylenetriaminepentaacetic acid uptake grossly overestimated glomerular filtration rate; in only 3 instances was the estimate within 20%. The accuracy of both formulas was better in older patients and in those with more normal renal function. We conclude that the Gates formula for measuring glomerular filtration rate is grossly inaccurate in children with diminished renal function and the Schwartz formula, although better, has a poor level of predictability.

Pyeloplasty in the young infant

The urgency, safety and benefits of performing pyeloplasty during the first weeks of life currently are being questioned. We reviewed our experience with 114 pyeloplasties in 103 infants and young children performed between 1983 and 1987. The 34 patients who underwent an operation before they were 3 months old were compared to 69 operated upon after 3 months. The surgical results in the 2 groups were equally good, with 90 per cent of the cases having an improved or stable postoperative excretory urogram or renal scan. Complications were few and were more common in the older age group, in which 7 children required a secondary procedure, including 2 for recurrent obstruction at the ureteropelvic junction. No patient in the younger age group required a secondary procedure for treatment of a complication or recurrent obstruction. Our findings indicate that the success of pyeloplasty performed during the first weeks of life is equal to that performed at a later patient age and were not more likely to be followed by a complication.

Changing concepts in management of primary obstructive megaureter

The management of neonatal urinary tract dilatations represents one of the most challenging dilemmas in pediatric urology today. We have been confronted with 44 renal units in 35 neonates diagnosed as having primary obstructive megaureter during the last 6 years. Of these units 23 in 17 infants were diagnosed antenatally and 20 (87 per cent) have been managed without surgical intervention. Notably, 16 renal units were graded as moderate to severe megaureters by an excretory urogram. The decision to manage conservatively was based on the initial extraction of the 99mdiethylenetriaminepentaacetic acid renal scan (the extraction factor). This estimate of absolute renal function has been used to differentiate dilatations with obstructive implications for the renal parenchyma from those without. Significantly, expectant treatment has resulted in improvement of dilatation on sequential excretory urograms in 15 megaureters and none has shown a deterioration of function by renal scan. Similar diagnostic criterion also has resulted in conservative management for 12 of 21 additional neonatal megaureters seen during this period with symptoms or they were discovered serendipitously. Only 2 of these 12 megaureters required surgical correction. The neonatal primary megaureter appears in many cases to represent a different entity than those that commonly presented before the advent of antenatal and perinatal diagnosis.