Lower urinary tract obstruction in the fetus and neonate

This article summarizes the most recent literature regarding congenital lower urinary tract obstruction in the fetus and newborn. Lower urinary tract obstruction is a heterogeneous group of rare diagnoses that have significant potential for in utero mortality and long-term morbidity in survivors. The diagnosis and management of the most common causes are reviewed. In addition, the current state of prenatal intervention for congenital lower urinary tract obstruction is discussed.

Genetic and developmental basis for urinary tract obstruction

Urinary tract obstruction results in obstructive nephropathy and uropathy. It is the most frequent cause of renal failure in infants and children. In the past two decades studies of transgenic models and humans have greatly enhanced our understanding of the genetic factors and developmental processes important in urinary tract obstruction. The emerging picture is that development of the urinary tract requires precise integration of a variety of progenitor cell populations of different embryonic origins. Such integration is controlled by an intricate signaling network that undergoes dynamic changes as the embryo develops. Most congenital forms of urinary tract obstruction result from the disruption of diverse factors and genetic pathways involved in these processes, especially in the morphogenesis of the urinary conduit or the functional aspects of the pyeloureteral peristaltic machinery.

Complete unilateral ureteral obstruction in the fetal lamb. Part I: long-term outcomes of renal hemodynamics and anatomy

PURPOSE

We evaluated the long-term consequences of complete fetal UUO on renal hemodynamics and anatomy.

MATERIALS AND METHODS

A total of 26 fetal lambs underwent surgical UUO at 90 days of gestation and 14 twin matched animals served as controls. Synchronous bilateral ARBF was measured using mean transit time technology. Standard anatomical analysis, including evaluation of RPV, was performed in the kidneys. Measurements were done 10, 20 and 40 days following UUO in groups 1 to 3, respectively and in 1-month-old lambs in group 4.

RESULTS

All obstructed kidneys underwent typical hydronephrotic transformations with a progressive decrease in parenchymal volume compared to that of contralateral and control kidneys. ARBF in obstructed kidneys was significantly decreased compared to their contralateral counterparts in all groups (p <0.01). Comparing ARBF to RPV showed that the decrease in ARBF was proportional to the loss of parenchymal volume in fetal obstructed kidneys but it remained significant in lambs (p <0.05).

CONCLUSIONS

Complete UUO alters ARBF, while vascularization of the remaining renal parenchyma is maintained in fetuses. Profound impairment of the renal arterial supply observed in lambs may be due to physiological changes linked to birth.

Complete Unilateral Ureteral Obstruction in the Fetal Lamb. Part II: Long-Term Outcomes of Renal Tissue Development

PURPOSE

We analyzed the dynamics of the renal tissue response to experimental fetal urinary flow impairment concerning renal morphology, extracellular matrix composition, regulators of connective tissue degradation and PAX2 protein expression.

MATERIALS AND METHODS

A total of 26 fetal lambs underwent surgical unilateral ureteral obstruction at 90 days of gestation and 14 twin matched animals served as controls. Kidneys were harvested 10, 20 and 40 days after the prior procedure in groups 1 to 3, respectively and in 1-month-old lambs (group 4). Morphological analysis was done using light microscopy. Picrosirius red staining was used to evaluate the area occupied by extracellular matrix components. Collagen I, III and IV, alpha-smooth muscle actin, MMP-1, 2 and 9, TIMP-1 and 2 and PAX2 protein were assessed using immunochemistry.

RESULTS

All obstructed kidneys were hydronephrotic without dysplasia. Hypoplasia resulting from a decreased NGG was observed. The inflammatory response to obstruction was poor in fetal obstructed kidneys. From 10 days after obstruction interstitial fibrosis was noted and confirmed by an increase in picrosirius red staining. In obstructed kidneys immunochemistry showed an increase in collagen deposition beginning from the papillae and extending through the whole parenchyma. Aberrant interstitial collagen IV deposition was observed. The increase in alpha-smooth muscle actin staining was mainly localized in the blastema and interstitial cells in obstructed kidneys. MMP and TIMP immunostaining was mainly present in tubules throughout the whole nephrogenic period and persisted in mature kidneys. Beginning from 20 days after obstruction a progressive increase in MMP and TIMP expression was noted. This was associated with ectopic expression in the medullary tubules. PAX2 protein was highly expressed in the nephrogenic zone, decreasing progressively to being markedly decreased in control lamb kidneys. No difference was found in PAX2 expression during the fetal period when comparing unobstructed and obstructed kidneys, it but remained strongly expressed in the dilated collecting ducts of obstructed lambs.

CONCLUSIONS

Complete unilateral ureteral obstruction performed in fetal lambs at 90 days of gestation led to pure hydronephrotic transformation, hypoplasia and a marked increase in connective tissue deposition. Inflammatory infiltrates and PAX2 dysregulation were not seen as having a decisive role in these modifications.

[Obstructive uropathy in childhood]

"Obstructive uropathy" is a generic term which combines different diseases in infants and childhood. Both the upper and lower urinary tract may be affected. Diseases of the urinary tract can cause an intrinsic obstruction. Sometimes tumours may cause a compression and as secondary effect an obstruction (extrinsic). Ultrasound is the key diagnostic tool and shows dilatation of the obstructed urinary tract. But for the functional exploration of babies and toddlers, renal scanning and X-ray examinations are necessary. These examinations lead to an exposure to radiation which necessitates careful indication. Some of the congenital diseases (for example ureteropelvic junction obstruction, megaureter) show a maturation without any intervention. So one has to decide whether to wait and see or to operate. A percutaneous nephrostomy or a DJ-catheter is not often used in the treatment of obstruction in general. These forms of drainage are more often used in the treatment of stones or of extrinsic obstruction. A pyelocutaneostomy or ureterocutaneostomy is a special surgical procedure in pediatric urology for transient drainage of the upper urinary tract (megaureter). The operation of a seriously ill new-born should be done in a centre for pediatric urology and pediatric nephrology. When the upper urinary tract is dilated, patients may need an antibiotic prophylaxis, because the dilatation of the upper urinary tract increases the risk of urinary tract infections (UTI). The indication for antibiotic prophylaxis should by guided by the criteria of the APN-Consensus Paper. Long-term follow-up is necessary and should comprise ultrasound, physical examination, controlling the blood pressure, urine analysis and blood tests. The aims of diagnostics, treatment and long-term follow-up are the preservation of renal function and to protect the children from UTI. This goal must be reached under conditions that are appropriate for children and their parents.

BIOMARKERS OF CONGENITAL OBSTRUCTIVE NEPHROPATHY: PAST, PRESENT AND FUTURE

PURPOSE

Congenital obstructive nephropathy constitutes one of the major causes of renal insufficiency in infants and children. This review addresses the need to define biomarkers that serve as surrogate end points for measuring the severity of obstruction, the evolution of renal maldevelopment and injury, and the response to medical or surgical intervention.

MATERIALS AND METHODS

The literature from the last 10 years was reviewed for biomarkers of congenital obstructive nephropathy. Sources of biomarkers included urine, blood, amniotic fluid, tissue and imaging techniques.

RESULTS

Previous markers of congenital obstructive nephropathy include sonographic renal pelvic diameter, quantitative diuretic renography, and markers of glomerular and tubular function. Attempts to correlate renal histological changes with differential renal function have been disappointing. Immunohistochemical analysis and laser capture microscopy should improve specificity. Most promising is the application of new insights into the cellular response of the developing kidney to urinary tract obstruction. These findings include components of the renin-angiotensin system, transforming growth factor-beta 1, monocyte chemoattractant protein-1 and epidermal growth factor. Microarray studies show unique patterns of gene expression by the neonatal rat kidney subjected to ureteral obstruction, and proteomics should provide even more sensitive biomarkers of obstructive nephropathy.

CONCLUSIONS

We must define the cellular and molecular bases of renal maldevelopment, focusing on the link between functional and developmental pathophysiology. These findings will lead to biomarkers that will optimize our management of congenital obstructive nephropathy.

Obstructive ureterocele?an ongoing challenge

Ureterocele is a cystic dilatation of the intravesical ureter that is most commonly observed in females and children, and usually affects the upper moiety of a complete pyeloureteral duplication. According to their position, ureteroceles are divided into intravesical, when the ureterocele is completely contained inside the bladder, and extravesical when part of the cyst extends to the urethra or bladder neck. Most ureteroceles are diagnosed in utero or immediately after birth during an echographic screening of renal malformations. Severe, febrile urinary tract infection is the most common postnatal presentation of ureteroceles, but they may, rarely, prolapse and acutely obstruct the bladder outlet. Once an ureterocele is identified sonographically, a voiding cystourethrogram to detect vesicoureteral reflux (VUR) and a 99m-technetium dimercapto-succinic acid renal scan to evaluate the function of the different portions of the kidney are mandatory. VUR in the lower pole is observed in 50% of cases and in the contralateral kidney in 25%. Simple endoscopic puncture of the ureterocele has recently been advocated as an emergency therapy for infected or obstructing ureteroceles and as an elective therapy for intravesical ureteroceles. The rate of additional surgery after elective endoscopic puncture of an orthotopic ureterocele ranges from 7 to 23%. Treatment of ectopic ureteroceles is more challenging and both endoscopic puncture and upper pole partial nephrectomy frequently require additional surgery at the bladder level. The reoperation rate after endoscopic treatment varies from 48 to 100%. It is 15 to 20% after upper pole partial nephrectomy if VUR was absent before the operation, but is as high as 50-100% when VUR was present. Thus, endoscopic incision is appropriate as an emergency treatment or when dealing with a completely intravesical ureterocele. Upper pole partial nephrectomy is the elective treatment for an ectopic ureterocele without preoperative VUR. In an ectopic ureterocele with VUR, no matter which type of primary therapy has been chosen, a secondary procedure at the bladder level, involving ureterocele removal and reimplantation of the ureter(s), should be anticipated.

Altered primate glomerular development due to in utero urinary tract obstruction

BACKGROUND

In utero urinary tract obstruction is an important cause of newborn and childhood renal failure. Ureteric obstruction during active nephrogenesis results in cystic renal dysplasia; the earlier and longer the obstruction the more severe the histopathological changes of dysplasia. We have reported on a non-human primate model of non-surgical in utero fetal ureteric obstruction that accurately reflects the human equivalent of obstructive renal dysplasia. A striking feature of this model is the effect of obstruction on normal glomerular development and podocyte survival.

METHODS

To study the effect of urinary obstruction on glomerular development, kidneys were studied from fetuses undergoing unilateral ureteric obstruction by ultrasound guided injection of alginate beads as early as 75 days gestation (term gestation = 165 +/- 10 days). These kidneys displayed all the features of human obstructive cystic dysplasia, had reduced weights, and significant deficiencies in terminal ureteric duct branching.

RESULTS

A combination of histochemistry, histomorphometry, and immunocytochemistry was used to demonstrate deficient cortical ureteric duct development and branching, reduced glomerular number, and altered glomerular basement membrane formation with in utero urinary tract obstruction.

CONCLUSIONS

These data suggest that urinary tract obstruction during active nephrogenesis results in a defect in ureteric duct branching morphogenesis, and altered vascularization of the glomerulus with consequent podocyte dropout and decreased glomerular number. These abnormalities reflect human renal dysplasia, which is associated with compromised postnatal renal function and, thus, should be predictive of postnatal outcome.

Deregulation of renal transforming growth factor-beta1 after experimental short-term ureteric obstruction in fetal sheep

Renal malformations are the commonest cause of chronic renal failure in children and they are often associated with urinary tract abnormalities that impair fetal urine flow. Up-regulation of transforming growth factor-beta1 (TGF-beta1) occurs after experimental postnatal urinary tract obstruction and we recently reported increased levels of TGF-beta1 in human renal malformations (Yang SP et al, Am J Pathol 2000, 157:1633-1647). These findings led us to propose that obstruction-induced stretch of developing renal epithelia causes up-regulation of TGF-beta1, which then perturbs renal development. In this study, therefore, we examined expression of components of the TGF-beta1 signaling axis in a previously characterized ovine model of fetal short-term urine flow impairment in which complete unilateral ureteric obstruction was induced at 90 days when a few layers of glomeruli had formed. Up-regulation of TGF-beta1 mRNA and protein was observed in obstructed kidneys, compared to sham-operated control organs, after only 10 days. Increased levels of TGF-beta1 receptors I (TGF-betaR1) and II (TGF-betaR2) were also detected on Western blot, and the cytokine and TGF-betaR1 co-localized in disrupted epithelia on immunohistochemistry. De novo expression of alpha-smooth muscle actin, a structural protein up-regulated during TGF-beta1-induced phenotypic switching between human renal dysplastic epithelial and mesenchymal lineages in vitro, was also observed in these aberrant epithelia. These findings implicate increased TGF-beta1 signaling in the early biological changes generated by fetal urinary tract obstruction.

Renal pelvic pressure responds with augmented increases to increments in intraabdominal pressure

BACKGROUND/PURPOSE

Flow of a fluid through a collapsible tube is under the influence of various factors including the external compressing pressure. Because the intraabdominal pressure may compress the ureter, an experimental study has been planned to determine and compare the normal intraabdominal and renal pelvic pressures and the alterations in renal pelvic pressure in response to the increments in intraabdominal pressure in the rabbits.

METHODS

Eight adult rabbits were used for the experiment. Under general anesthesia, an urethral catheter, a nasogastric tube, and an intraperitoneal catheter were placed to measure intravesical (IVP), intragastric (IGP), and intraabdominal pressures (IAP), respectively. Intracranial pressure monitorization catheter was placed into the renal pelvis to monitor intrapelvic pressure (IPP). Basal pressure measurements have been recorded. The pressures have been recorded in every 5 minutes, and IAP has been increased gradually about 3 to 4 cm of water pressure in every step for 30-minute periods.

RESULTS

Increases in the intrapelvic pressure values have been significantly higher than the increases in the IAP (P < .001). A significant correlation has been found between IPP and IAP (P = .000, r = 0.866). By using linear regression analysis the relationship has been found to be IPP = 7.303 + 1.985 (IAP). Intragastric pressure values have been higher compared with IAP values (P < .001), whereas intravesical pressures have not differed from IAP (P > .05).

CONCLUSIONS

Elevations in IAP results in augmented increases in the IPP. Poiseuille and Laplace Laws suggest this augmented increase to resemble proximal ureteric obstruction. Increases in IAP may simulate proximal ureteric obstruction and may take part in the pathogenesis of hydronephrosis. J Pediatr Surg 36:901-904.

Early fetal obstructive uropathy produces Potter's syndrome in the lamb

BACKGROUND

If creating an obstructive uropathy early in glomerulogenesis produces MCDK (Multicystic Dysplastic Kidney), then a very early obstruction may produce Potter's Syndrome (PS) with oligohydramnios.

METHODS

Fetal lambs at 50 days' gestation underwent urethral and urachal ligation using fine SILASTIC (Dow Corning, Midland, MI) tubing and were delivered by cesarean section at 145 days' gestation. At the time of death, kidney weight, length, and lung volumes were measured. These samples were examined histologically. Urinary sodium, chloride, potassium, and osmolarity also were measured. These were compared with normal-term fetuses.

RESULTS

One ewe miscarried. Two of 3 of 50-day obstructive uropathy lambs survived. The 2 survivors had dysplastic kidneys. One with large gastroschisis did not have PS but the other had renal, pulmonary, and chest wall hypoplasia. Both male lambs had undescended testes with a large bladder. Kidney weights were 2 g in the PS lamb and 16 g in controls. Lung volume was 84 mL in the PS lamb and 340 mL in controls. The lamb's face was compressed and the fetus was hydropic. Urine sodium, potassium, and osmolarity levels were higher than that of controls.

CONCLUSIONS

This is the first successful model ligating the penile urethra and urachus in a 50-day lamb. The authors' previous 60-day model did not have PS, but an earlier obstructive uropathy caused MCDK with PS.

How they begin and how they end: classic and new theories for the development and deterioration of congenital anomalies of the kidney and urinary tract, CAKUT

CAKUT are problems that often require surgical intervention or, in the worst case, lead to renal failure and the need for dialysis and/or renal transplantation. It is believed that these anomalies share a common genetic cause and to date there has been no good animal model with which to study these abnormalities. Although the abnormal interaction between the ureteral bud and metanephric blastema leads to renal hypodysplasia, vesicoureteral reflux, and ectopic ureters to name a few, the genetic and biochemical modulation of urinary tract development is not understood. Studies using the mouse strain mutant for angiotensin type 2 (AT2) receptors have given new insight into this mystery. The animals show defective apoptosis of undifferentiated mesenchymal cells in the area surrounding the developing kidney and urinary tract. This abnormal apoptosis may well interfere with the normal interaction between the ureteral bud and metanephric blastema resulting in CAKUT. This abnormal interaction would theoretically lead to preexisting intrinsic abnormalities of the kidney, which are programmed and take effect early in embryonic development. In the worst cases, the renal abnormalities would lead to progressive deterioration of renal function. Undoubtedly, there are more genes and biochemical modulators involved in this process other than the RAS and AT2 receptors. Our current animal model gives new and unique possibilities with which to study development of the kidney and urinary tract and ultimately seek ways of preventing an often debilitating disease process.

Short-term urinary flow impairment deregulates PAX2 and PCNA expression and cell survival in fetal sheep kidneys

Renal malformations account for most children with chronic renal failure and are often associated with urinary tract anatomical obstruction. We examined cellular and molecular events after experimental urinary flow impairment in fetal sheep. Ovine gestation lasts 144 to 150 days with the metanephros appearing at 27 to 30 days. We generated complete unilateral ureteric anatomical obstruction at 90 days when a few layers of glomeruli had formed. After 10 days, we recorded ureteric and pelvic dilatation with renal parenchymal weight greater than contralateral organs or those from unoperated fetuses. The nephrogenic cortex was replaced by disorganized cells separated by edema and prominent vascular spaces. Cortical histology was dominated by cysts associated with malformed glomerular tufts. Cystic epithelia expressed PAX2, a growth-stimulating transcription factor down-regulated during normal maturation, and proliferating cell nuclear antigen, a surrogate marker of cycling cells. Detection of apoptosis using propidium iodide and in situ end labeling showed a significant increase of the point prevalence of death in the obstructed cortex. Hence, PAX2 and proliferating cell nuclear antigen expression as well as death were deregulated, as we previously reported in human kidney malformations. Medullary collecting ducts and loops of Henle were also disrupted, correlating with impaired urinary dilution and sodium reabsorption. Therefore, complex aberrations of morphogenesis, gene expression, cell turnover, and urine composition occur relatively early after experimental impairment of fetal urinary flow.

Rearrangement of the human CDC5L gene by a t(6;19)(p21;q13.1) in a patient with multicystic renal dysplasia

Genetic studies have implicated the short arm of chromosome 6 in congenital hydronephrosis. In previous studies, we described a fetus carrying a t(6;19)(p21;q13.1) as the sole cytogenetic anomaly and suffering from bilateral multicystic renal dysplasia caused by a bilateral complete pelviureteric junction obstruction, resulting in a massive hydronephrosis. Characterization of the chromosome 19 breakpoint region revealed that the transcription factor-encoding USF2 gene is affected. In this report, we show that the CDC5L gene on chromosome 6p is rearranged in the cells of the fetus. CDC5L encodes a protein that is related to the product of the Schizosaccharomyces pombe Cdc5 gene, which exerts its effects at the G2/M transition during cell cycle progression. We have established the genomic organization of the CDC5L gene and found that it consists of at least 16 exons spanning approximately 50 kb of chromosome segment 6p21. Northern blot analysis indicated that the gene is ubiquitously expressed as a single mRNA of about 3.4 kb in both fetal and adult tissues. The translation product of the CDC5L gene has an electrophoretic mobility of about 100 kDa and is predicted to be a nuclear protein, since it contains a Myb-related DNA binding domain and potential nuclear localization signals in its aminoterminal region. Immunocytochemical analysis confirmed the nuclear localization of the CDC5L protein. CDC5L was also predicted to contain a hydrophilic, proline-rich region in its central part, which might function as a transcriptional activating domain. The chromosome 6 breakpoint was found in the intron between exons 9 and 10, indicating that, as a direct result of the 6;19 translocation, the Myb-related DNA binding domains and the nuclear localization signals are separated from the putative transactivating domain. Northern blot and RT-PCR experiments revealed that the other CDC5L allele is unaffected, and in Western blot experiments, expression of the 100-kDa protein was detected in fibroblasts of the fetus. Expression of a truncated or hybrid CDC5L transcript resulting from the CDC5L rearrangement could not be demonstrated.

Isolation of cosmids corresponding to the chromosome breakpoints of a de novo autosomal translocation, t(6;19)(p21;q13.1), in a patient with multicystic renal dysplasia

Hydronephrosis caused by pelvi-ureteric junction obstruction (PUJO) is a frequent urological malformation assumed to result from a deficient development of the ureteric bud. The exact etiology of pelvi-ureteric junction stenosis is unknown, but there is convincing evidence for a genetic cause, with linkage analysis predicting a hereditary hydronephrosis locus on chromosome 6p. We encountered a patient with a de novo autosomal t(6;19)(p21;q13.1) and attendant bilateral multicystic renal dysplasia (MRD), bilateral PUJO resulting in massive hydronephrosis, and an associated von Mayer-Rokitansky-Kuster disorder. On the basis of the presumption that in this patient the putative hydronephrosis gene might be disrupted by the translocation, we sought to isolate DNA from the breakpoint regions as the initial step in a strategy to identify genes affected by the t(6; 19). Using sequential rounds of fluorescence in situ hybridization (FISH) with cosmids selected from a detailed integrated map of the long arm of chromosome 19, we have identified a cosmid clone that spans the breakpoint. The position of the breakpoint was further localized by Southern blot analysis. Using a vectorette PCR approach, rearranged DNA fragments were isolated and, by comparative nucleotide sequence analysis, these were shown to contain ectopic sequences. A cosmid clone containing these ectopic sequences was isolated and shown by CASH (chromosome assignment using somatic cell hybrids) and FISH (fluorescence in situ hybridization) analysis to map to the short arm of chromosome 6 and to span the breakpoint found in the MRD patient. The isolated cosmid clones are useful reagents for analysis of other MRD patients and for the search for genes at or flanking the breakpoints.

Expression of cell growth regulated genes in the fetal kidney: relevance to in utero obstruction

Previous studies of fetal urinary tract obstruction (bladder outlet obstruction and ureteral obstruction) in lambs have shown that obstructions created relatively early in gestation (4/10 to 6/10 term) can significantly affect growth of the developing kidney. This suggests that urinary tract obstruction in utero can alter normal mechanisms of kidney growth. However, a mechanism for these effects has not yet been proposed. In this study we have used mRNA expression analysis to characterize the temporal sequence of expression of several growth-regulated genes during normal ovine kidney development. The purpose of this study was to test the hypothesis that early obstructions, such as those believed to arise in congenital obstructive uropathy in humans, might have a disproportionate effect on hyperplastic growth if the cellular growth fraction (percent of cells in the organ undergoing DNA synthesis) was greater in the second trimester than in the last. Northern blot analysis of the cell cycle-dependent genes histone H3, c-myc and ornithine decarboxylase (ODC) indicated a progressive, gradual decline in cellular proliferation in the kidney from approximately 60 to 135 days (4/10 term to term) gestation, as evidenced by decreases in the respective mRNA levels. The greatest levels of cell proliferation occurred near the midpoint of gestation. This indirect measurement of decline in cellular growth fraction was reflected in direct measurements of change in relative kidney weight. To test whether this decline in mRNA levels occurs widely among genes expressed in the fetal kidney during this period, relative expression levels of more than 300 anonymous mRNA transcripts were evaluated by differential display analysis. This method showed that genes whose expression patterns resembled the growth-regulated genes constituted less than 5% of the expressed mRNAs identified. These data indicate that intrauterine urinary tract obstructions that arise at or near the midpoint of gestation coincide with the highest rates of cell proliferation occurring in the second and third trimesters and, therefore, might adversely affect mechanisms of cell proliferation.

Fetal compensatory renal growth due to unilateral ureteral obstruction

To determine whether fetal compensatory renal growth occurs in response to early gestational unilateral renal obstruction and to help elucidate the characteristics of this response, a fetal lamb model was developed in which unilateral ureteral obstruction was created at 60 days of gestation (term 135 to 140 days) and the effects of the obstruction were studied at varying periods thereafter. Kidneys were retrieved at 2 weeks (75 days in 3 cases), 5 weeks (95 days in 4) and 10 weeks (135 days in 9) after obstruction, weighed and preserved for histology and biochemical studies. Deoxyribonucleic acid (DNA), ribonucleic acid and protein were quantitated using standard assays. Morphometric studies to estimate glomerular number were performed using standard stereological methods. Contralateral kidney weight was increased compared to normals in 55 cases at all ages. The relative difference increased from 75 to 95 days. The fractional increase at 135 days (49.5%, p < 0.001 versus normal) was not different from 95 days (46.4%, p = 0.87), indicating that growth rate acceleration occurred predominantly before 95 days. Total renal DNA was increased above normal at each time point, with an ultimate increment proportionate to weight. Protein concentration was unchanged, suggesting that weight increase was not due to changes in renal water. Protein/DNA ratios were unchanged, indicating a predominantly hyperplastic process. Ribonucleic acid/DNA ratios decreased, possibly indicating a high rate of proliferation. Total glomerular number at term did not increase with in utero compensatory renal growth. Unilateral ureteral obstruction created early in gestation produced compensatory renal growth of the intact kidney in the fetal lamb. This process demonstrates an early but transient growth rate acceleration, hyperplasia and no increase in total glomerular or nephron number. The occurrence of compensatory renal growth in the fetal kidney with minimal functional renal demand would suggest that its mechanisms may be independent of functional demand. This model is unique and well suited to study compensatory renal growth.

Endoscopic incision of persistent ureteral infoldings

We report 2 cases of persistent ureteral infolding in a four-month-old infant and an eight-year-old boy, both presenting with hydronephrosis. Initial diagnostic evaluation showed multiple pleats in the upper ureter. Endoscopic incision of the pleats relieved hydronephrosis. The concept of persistent ureteral infolding seems to apply to these cases.

The response of the fetal kidney to obstruction

In a fetal ovine model the renal effects of different anatomic levels of fetal urinary obstruction were studied. Parameters of prenatal renal growth and differentiation were characterized and correlated with the patterns of renal response to in utero obstruction. Complete ureteral or urethral obstruction was produced in the sheep fetus at 55 to 60 days of gestation. Animals were delivered and sacrificed at near term (140 days), and the kidneys were removed and prepared for analysis. Parameters examined included weight, histology, glomerular number and total surface area, as well as urinary sodium, creatinine, osmolarity and N-acetyl glucosaminidase. Three patterns of response were identified, producing hydronephrotic, cystic or dysgenetic kidneys. Hydronephrotic kidneys were usually the result of bladder outlet obstruction or ureteral obstruction with spontaneous urinary decompression. These kidneys were large (20.7 gm. versus normal 10.8 gm., p less than 0.0001), with thinning of cortical parenchyma that was structurally intact. Glomerular number and surface area were normal. Cystic kidneys were large (14.2 gm., p less than 0.05) with grossly visible cysts and an effaced medulla. Cortical structure was distorted by cysts but basic elements were intact. Glomerular number and surface area were not reduced. Dysgenetic kidneys were small (3.9 gm., p less than 0.0001) with markedly abnormal cortical structure and little recognizable medulla. Histological elements similar to fetal structures were present, including cuboidal/columnar tubular epithelium and peritubular mesenchymal collars. Glomerular number and surface area were significantly less than normal (p less than 0.001). The kidneys contralateral to unilaterally obstructed kidneys were significantly larger than normal (16.2 gm., p less than 0.0001), with normal histology, glomerular number and surface area, indicating in utero contralateral renal hypertrophy. Urinary sodium was variably affected in the hydronephrotic kidneys and was identical to plasma in the dysgenetic kidneys. These results indicate the technical feasibility of in utero models of urinary obstruction. Renal growth and patterns of differentiation were markedly affected by in utero obstruction. They should be a major focus in the investigation of congenital obstructive uropathy, since normal processes of renal growth and differentiation form the basis for postnatal function.

Suspected pyelo-ureteral junction obstruction in the fetus: when to do what? II. Experimental viewpoints

Nowadays the postnatal management of antenatally detected hydronephrosis is much debated. Some authors claim that these cases ought to be operated very early, since there is rapid renal destruction and full recovery may only be achieved during this period. Others claim the opposite and recommend a nonoperative follow-up, provided that renal function is normal, as it is in the majority of cases. If experimental studies are to be used to settle this question, the created obstructions must correspond to human obstructions. That is, be partial and permanent, produced in fetal or newborn animals, preferably be moderate in degree, the diameter should grow in pace with the growing ureter, and be followed for a long period. Only three experimental series fulfil, to some extent, these requirements. In two of them a severe obstruction was produced, which within 5-8 weeks led to reductions by 80-95% in renal blood flow, glomerular filtration and potassium and phosphate excretions, which were in part compensated for and established early. In one study, a moderate obstruction was created which within 9 weeks led to reductions of 10-30% in renal blood flow, glomerular filtration, and potassium excretions, which were in part compensated for. The changes appeared very soon but were not progressive. Release of the obstruction had to be performed very early in order to avoid the lesions. The causes of the renal defects and of the absence of progression are discussed. It is concluded that the majority of human pyeloureteral obstructions are best imitated by a moderate type obstruction. The results do not support any rationale for early correction.(ABSTRACT TRUNCATED AT 250 WORDS)

Embryogenesis of ureteral anomalies: a unifying theory

Extensive gross, microscopic and clinical studies of various ureteral anomalies have enabled investigators to set forth theories regarding the aetiologies of these anomalies consistent with observed fact. Synthesis of these observations allows for a simplified classification of mega-ureter (primary obstructed, reflux and non-obstructed, non-reflux mega-ureters), ureterocele, duplex ureters and ectopic ureters based upon some combination of mesenchymal differentiation anomalies and location anomalies. A defect early in mesenchymal differentiation would be expected to result in panureteral disease. A defect later in development would result in a focal abnormality anywhere along the course of the ureter. Influence upon ureteral bud mesenchyme by local expansion factors in the bladder base may result in various types of ureterocele. Position of the ureteral orifice on the trigone or in Wolffian duct derivatives would occur in accordance with the Weigert-Meyer principle and would correlate with upper tract dysplasias. Thus, an attempt has been made to systematize and trace the origins of mega-ureter, ureterocele, duplex ureters and ectopic ureters to defects of differentiation of the basic mesoblastic cell in aberrant locations of the ureteral bud.

Correction of congenital hydronephrosis in utero III. Early mid-trimester ureteral obstruction produces renal dysplasia

Is the renal dysplasia (RD) commonly seen in babies with urinary tract obstruction a developmental consequence of the obstruction or is it an associated embryologic malformation? We produced complete unilateral ureteral obstruction in six 58- to 66-day old lamb fetuses by clipping a silastic ring on the ureter. Three fetuses survived to term. All obstructed kidneys were not only grossly hydronephrotic but dysplastic by histologic criteria; ie, parenchymal disorganization, primitive epithelial structures, and marked fibrosis. The contralateral unobstructed control kidneys were normal. The changes were similar to those seen in the human neonate with obstruction and RD, suggesting that in this model RD was caused by obstruction to the flow of urine early in fetal development.

The pathogenesis of renal dysplasia. III. Complete and incomplete urinary obstruction

We graded obstructed kidneys of infants on the hypodysplasia scale to assess the influence of complete and partial obstruction on the pathogenesis of hypodysplasia. Kidneys with complete obstruction exhibited severe grades; those with partial ureteral obstruction had near normal grades. Those kidneys subjected to partial urethral obstruction ranged from mild to severe grades which correlated with degrees of lateral ectopy of the urethral office. Renal parenchymal development was impaired by complete obstruction but was tolerant to incomplete obstruction. Abnormal orifice positions associated with urethral obstructions were considered to be manifestations of ectopic ureteric buds and the hypodysplasia to be evidence of abnormal induction of abnormal renal blastema.

Valves of the ureter as a cause of primary obstruction of the ureter: anatomic, embryologic and clinical aspects

The causes of obstruction of the ureter at the ureteropelvic and ureterovesical junctions are still controversial. In this study portions of obstructed ureters were excised at operation or autopsy and the suspected sites of obstruction were examined anatomically, radiographically and histologically. A valvular mechanism caused obstruction in 15 of 27 specimens. The valve lay at the junction of the dilated and undilated segments of the ureter. The internal anatomy of this site was hidden from external view by the fascia overlying the ureter and was demonstrated by contrast ureterograms. The axes of the lumina of the dilated and undilated segments were eccentric and the walls of the ureter overlapped at the site of obstruction to form a common wall, which created a valve effect. The valve flaps were visualized radiographically as a filling defect. The valve obstructed antegrade but not retrograde flow. Anatomic dissection or serial sections of blocks of the valve zone demonstrated that either a single or a double flap caused obstruction. The valve was coapted against the opposite wall of the distal segment by the pressure generated in the dilated ureter during antegrade flow. The muscle of the unobstructed segment of ureter distal to the valve appeared normal histologically, whereas the muscle of the obstructed proximal segment was hypertrophic.

Embryologic basis for lower ureteral anomalies: a hypothesis

A hypothesis for the embryogenesis of lower ureteral anomalies invokes variations in location and number of ureteral buds on the mesonephric duct. Such vagaries determine the length of the common nephric duct and the time of meeting of the ureteral bud (or buds) with the urogenital sinus. These factors in turn affect the density of the mesenchymal tissue and its mass in relation to the adjoining structures and, ultimately, the musculature of the trigone as well as the level of the ureteral hiatus and the musculature of the bladder base. Primary reflux, ureteral ectopy, ureteral duplication, ureterocele, functional ureteral obstruction, and congenital strictures are viewed and possibly explained in the light of the embryonal variations mentioned.