Ultrasound Imaging of the Renal Parenchyma of Premature Neonates for the Assessment of Renal Growth and Glomerulomegaly

Radial Expansion of the Nephrogenic Zone in the Fetal Human Kidney During Advanced Pregnancy: A Microanatomical Look at a Little Noticed Process

Introduction: The experiences with preterm and low birth weight babies indicate a special vulnerability of their kidneys, since different kinds of noxae can evoke the termination of nephron formation. This leads to oligonephropathy, which is associated with serious consequences for health in the later stages of life. While the clinical aspects have been intensely investigated, only few pathological data point to the initial traces left by the noxae. Up to this date, only the reduction in the width of the nephrogenic zone (NZ) and the lack of here occurring basophilic S-shaped bodies were reported. Methods and Materials: The relationship between the arising nephron and its structural neighbors changes throughout the developmental progress. Locally, this determines the vertical width of the NZ reflected by the radial expansion of both the parenchyma and the interstitium. Since information about the origin, the site, and the involved structures is not available, the related microanatomical features were recorded. Results: The data reveal that the renal vesicles, comma-shaped bodies, and S-shaped bodies are unequally distributed in the NZ. Due to their progressive sizes, it has an influence on the local vertical width of the NZ. This parameter is registered as the distance between the inner side of the renal capsule and the proximal pole of the respective stage of the nephron anlage. The vertical width can be further subdivided: the constant height of the district of progenitor cell recruitment and the variable height of the area of nephron shaping. Exclusively here, the radial expansion of the shaping nephron stages can be noticed. It starts at the section border between the head and the conus of the related collecting duct ampulla by positioning the primitive renal vesicle. While the respective proximal pole stays mounted next to the connecting tubule of a previously developed nephron, the distal pole sticks between the head and the conus at the CD ampulla for linking the future connecting tubule. This causes that henceforth the medial aspect of the extending renal vesicle, comma-shaped body, or S-shaped body stages radially expands in close proximity to the elongating conus of the CD ampulla. Conclusion: Between the arising nephron stages and the elongating conus of the CD ampulla, a linked radial expansion occurs. This new finding is essential to identify the extent of targeting of noxae that subsequently leads to a reduction in the width of the NZ.

The relationship between maternal health during pregnancy and infant kidney development: a prospective cohort study

BACKGROUND

The significance of intergenerational impacts on fetal and infant kidney development and function remains to be fully understood. This is particularly relevant for certain populations, for example the Indigenous Australians since their risk of developing chronic kidney disease (CKD) is twice that of non-Indigenous Australians. The aim of this study was to assess the impact of maternal health and kidney size and function on infant kidney development.

METHODS

This study was open to all pregnant women receiving antenatal care at Townsville University Hospital, Australia. It presents data from a larger, ongoing prospective, longitudinal cohort study which commenced August 2019, involving mother-infant dyads. This manuscript reports on term mother-infants' dyads from singleton pregnancies. Ultrasound was used to measure renal parenchymal thickness, a surrogate for nephron number, of the mother and their newborn. Kidney function was assessed using serum cystatin C and creatinine.

RESULTS

Analysis was conducted on 80 mother-infant dyads, 17 Indigenous and 63 non-Indigenous. Multivariate regression modeling showed maternal renal parenchymal thickness (ß = 0.31, p = 0.004), smoking (ß = - 0.70, p = 0.022) and maternal serum cystatin C (ß = - 0.34, p = 0.014) significantly predicted newborn renal parenchymal thickness. No significant differences were found between the maternal and newborn renal parenchymal thickness and function between Indigenous and non-Indigenous participants.

CONCLUSIONS

Our study suggests that maternal kidney size and function has a significant intergenerational effect on kidney development of their infants. Newborn renal parenchymal thickness was positively associated with maternal renal parenchymal thickness and negatively associated with smoking and maternal serum cystatin C.

Intrauterine life to adulthood: a potential risk factor for chronic kidney disease

Multiple risk factors for chronic kidney disease (CKD), one of the major causes of morbidity and mortality in the adult population globally, have been identified, including older age, male gender, family history, smoking, diabetes mellitus, hypertension, ischaemic heart diseases and various medications. Preterm delivery, affecting >10% of the newborns in the USA, is a global concern with increasing incidence in recent decades. Preterm birth has been linked to multiple medical comorbidities such as diabetes mellitus, hypertension and cardiovascular diseases, while its association with CKD has recently been investigated. Prematurity and intrauterine growth restriction (IUGR) have been associated with an increased risk for CKD, specific histopathological examination findings and CKD-associated risk factors such as diabetes mellitus, hypertension and dyslipidaemia. In this narrative review, our aim is to evaluate and summarize the association between the risk for CKD and prematurity, low birthweight and IUGR along with potential underlying pathophysiological mechanisms.

Kidney growth following preterm birth: evaluation with renal parenchyma ultrasonography

BACKGROUND

Preterm birth impairs nephrogenesis, leading to a reduced nephron endowment which is inextricably linked to hypertension and chronic kidney disease in adults. The aim of this study was to compare nephron endowment between preterm infants to that of intrauterine fetuses at the same gestational age (GA) using a novel indirect ultrasound measurement of the renal parenchymal thickness. We hypothesized that extrauterine and intrauterine renal parenchymal thickness would differ based on altered renal growth environments.

METHODS

In this observational study, appropriately grown preterm infants (birth weight of between the 5th and 95th percentile) born <32 weeks, admitted to the neonatal department were eligible to participate. Renal parenchymal thickness of the infants was measured at 32- and 37-weeks postmenstrual age (PMA). These measurements were compared to the intrauterine renal parenchymal thickness of appropriately grown fetuses (control).

RESULTS

At 32-weeks PMA, the preterm infants had a significantly thinner renal parenchyma compared to fetuses at 32-weeks GA suggesting they had less nephrons, however by 37-weeks there was no significant difference in renal parenchymal thickness.

CONCLUSIONS

We propose that the differences in the extrauterine growth of the renal parenchyma in preterm infants may be due to a reduced number of nephrons and compensatory hyperfiltration.

IMPACT

This article provides insight into the effects of prematurity on nephrogenesis by comparing extrauterine renal parenchymal growth of born preterm infants to the ideal intrauterine fetal growth. Renal parenchyma thickness measurement using ultrasonography is a novel non-invasive measurement of renal development for the determination of nephron endowment. Differences in the renal parenchymal thickness of the preterm infants may be due to a deficit in nephron number and compensatory hyperfiltration.

Quantitative Evaluation of Renal Cortex Perfusion Using Contrast-Enhanced Ultrasound Imaging Parameters in Ischemia-Reperfusion Injury in Rabbits

The aim of this study was to evaluate blood perfusion of the renal cortex during ischemia-reperfusion (I/R) injury using quantitative contrast-enhanced ultrasound (CEUS) parameters. In this experiment, 24 rabbits were randomly divided into four groups (N = 6): sham-operated group, 24-h post-operation for I/R injury group (24-h I/R), 3-d post-operation for I/R injury group (3-d I/R) and 5 d post-operation for I/R injury group (5 d I/R). All quantitative CEUS parameters were monitored and included the gradient from the start frame to the peak frame (Grad), area under the curve (Area), time-to-peak (TTP), difference between B(intercept intensity at t=0) and A(the intensity attenuation t= 0) and arrival time (AT). Subsequently, we analyzed the changes in these parameters, as well as the correlation between changes in CEUS parameters and pathological parameters. AT and TTP values peaked 3 d after I/R surgery, which correlated with the most significant pathological changes at the same time point. These parameters (such as AT, TTP and Grad) may be useful in dynamically monitoring the severity of tissue damage at the early stage of I/R injury.

Prematurity, perinatal inflammatory stress, and the predisposition to develop chronic kidney disease beyond oligonephropathy

Prematurity and perinatal stress, such as intrauterine growth restriction (IUGR) and chorioamnionitis, are pathological processes creating an impaired intrauterine environment. These intrauterine factors are associated with the development of proteinuria, hypertension, and chronic kidney disease (CKD) later in life. Initially, this was thought to be secondary to oligonephropathy, subsequent glomerular hypertrophy, and hyperfiltration, leading to glomerulosclerosis, a further decrease in nephron number, and finally CKD. Nowadays, there is increasing evidence that prematurity and perinatal stress affect not only nephron endowment but also the maturation of podocytes and vasculogenesis. IUGR is associated with podocyte damage and an aggravated course of nephrotic syndrome. Moreover, preterm birth and IUGR are known to cause upregulation of the postnatal renin-angiotensin system, resulting in hypertension. Chorioamnionitis causes damage to the glomeruli, thereby predisposing to the development of glomerulosclerosis. This review aims to summarize current knowledge on the influence of prematurity, IUGR, and chorioamnionitis on the development of different glomerular structures. After summarizing human and experimental data on low nephron number in general, a specific focus on the current understanding of podocyte and glomerular capillary formation in relation to prematurity and different causes of perinatal stress is presented.

Can measurement of the foetal renal parenchymal thickness with ultrasound be used as an indirect measure of nephron number?

Chronic kidney disease continues to be under recognised and is associated with a significant global health burden and costs. An adverse intrauterine environment may result in a depleted nephron number and an increased risk of chronic kidney disease. Antenatal ultrasound was used to measure the foetal renal parenchymal thickness (RPT), as a novel method to estimate nephron number. Foetal renal artery blood flow was also assessed. This prospective, longitudinal study evaluated the foetal kidneys of 102 appropriately grown and 30 foetal growth-restricted foetuses between 20 and 37 weeks gestational age (GA) to provide vital knowledge on the influences foetal growth restriction has on the developing kidneys. The foetal RPT and renal artery blood flow were measured at least every 4 weeks using ultrasound. The RPT was found to be significantly thinner in growth-restricted foetuses compared to appropriately grown foetuses [likelihood ratio (LR) = 21.06, P ≤ 0.0001] and the difference increases with GA. In foetuses with the same head circumference, a growth-restricted foetus was more likely to have a thinner parenchyma than an appropriately grown foetus (LR = 8.9, P = 0.0028), supporting the principle that growth-restricted foetuses preferentially shunt blood towards the brain. No significant difference was seen in the renal arteries between appropriately grown and growth-restricted foetuses. Measurement of the RPT appears to be a more sensitive measure than current methods. It has the potential to identify infants with a possible reduced nephron endowment allowing for monitoring and interventions to be focused on individuals at a higher risk of developing future hypertension and chronic kidney disease.

Case report: increased single-nephron estimated glomerular filtration rate in an adult patient with low birth weight

BACKGROUND

Low birth weight (LBW) is associated with end-stage kidney disease and hypertension and is considered to be a surrogate marker of low nephron number. Low nephron number is hypothesized to contribute to glomerular hyperfiltration that may cause kidney injury; however, this is not yet proven. Until now, the hyperfiltration in LBW patients has not been shown directly yet.

CASE PRESENTATION

A 23-years-old female was referred with the persistent proteinuria and decreased renal function (estimated glomerular filtration rate by cystatin C (eGFRcys); 41.86 ml/min). She was a premature baby with low birth weight (704 g, 24 gestational weeks). Renal biopsy demonstrated focal segmental glomerulosclerosis (FSGS) of the perihilar variant with expanded glomerular diameter. We calculated the single-nephron estimated glomerular filtration rate (SN-eGFR) that was higher than that of the same age group in the healthy living kidney donors and speculated that glomerular hyperfiltration is a pathophysiological cause of FSGS.

CONCLUSION

This is the first case of SN-eGFR measurement in a patient with LBW. The increased SN-eGFR in this case provides an important insight into the pathophysiological mechanisms of LBW for its progression to kidney disease.

Altered in utero kidney development in newborns with congenital heart disease

BACKGROUND

It is known that the heart is not the only organ affected in congenital heart disease (CHD); there is growth restriction of both the brain and the whole body. The protective mechanism of "the brain-sparing phenomenon" re-directs blood flow toward the growing brain in fetuses with CHD. We hypothesized that these changes would result in impaired fetal kidney growth.

METHODS

The preoperative ultrasound measurements of kidney length were obtained retrospectively from 452 neonates requiring surgery for CHD. Percentiles were generated based on regression analysis of normative kidney length from three datasets according to both corrected gestational age and to birthweight.

RESULTS

As a cohort, neonates with CHD have significantly enlarged kidneys, with a mean percentile ranging from 54.1-72.7 (p < 0.001), depending on the three normal population datasets used for comparison. The kidneys of neonates with left heart obstruction were consistently demonstrated to be greater than normal, unlike those with cyanotic heart disease which were shown to have either normal or enlarged kidneys, depending on the reference population used.

CONCLUSIONS

The kidneys of newborns with CHD are not reduced in size, and on average are larger than normal. The nature of this size discrepancy and its subsequent clinical significance is unknown.

Prematurity and future kidney health: the growing risk of chronic kidney disease

PURPOSE OF REVIEW

The purpose of this review is to describe the role prematurity plays in the development of chronic kidney disease (CKD) and to discuss potential reasons for this association including decreased nephron mass, as well as postnatal insults such as neonatal acute kidney injury (nAKI).

RECENT FINDINGS

New observational studies in humans and experimental studies in animal models have strengthened the association between prematurity, low birth weight and CKD. Growing evidence suggests increased susceptibility to CKD is caused by decreased nephron mass at birth. Beginning with a low nephron count may cause only subtle abnormalities during childhood, however may result in CKD, hypertension and albuminuria in adolescence or adulthood. Recent studies in premature infants reveal a high incidence of nAKI, which may also contribute to ongoing CKD risk.

SUMMARY

Children born at low birth weights (both due to prematurity and/or intrauterine growth restriction) show increased risk of kidney dysfunction during adulthood. A better understanding of the modulators of nephron mass in premature infants as well as the effects of the extrauterine environment is essential. Additionally, improved awareness of at-risk infants is important as is early evaluation and detection of kidney dysfunction, allowing interventions to slow the progression to CKD.