Magnetic resonance imaging detected renal volume reduction in refluxing and nonrefluxing kidneys

Imaging studies and biomarkers to detect clinically meaningful vesicoureteral reflux

The work-up of a febrile urinary tract infection is generally performed to detect vesicoureteral reflux (VUR) and its possible complications. The imaging modalities most commonly used for this purpose are renal-bladder ultrasound, voiding cystourethrogram and dimercapto-succinic acid scan. These studies each contribute valuable information, but carry individual benefits and limitations that may impact their efficacy. Biochemical markers are not commonly used in pediatric urology to diagnose or differentiate high-risk disease, but this is the emerging frontier, which will hopefully change our approach to VUR in the future. As it becomes more apparent that there is tremendous clinical variation within grades of VUR, the need to distinguish clinically significant from insignificant disease grows. The unfortunate truth about VUR is that recommendations for treatment may be inconsistent. Nuances in clinical decision-making will always exist, but opinions for medical versus surgical intervention should be more standardized, based on risk of injury to the kidney.

Analysis of Kidney Ultrasound Dimensions by Body Habitus and Position

PURPOSE

Renal dimensions are an important assessment of the genitourinary tract used to evaluate critical aspects of renal growth and development. Understanding the effect of patient position is important to use and interpret these parameters. In this prospective study we determined the effect of patient position and general body habitus on renal length and parenchymal area in children undergoing renal ultrasound.

MATERIALS AND METHODS

Between October 2010 and January 2011 children underwent renal ultrasound while prone and supine. Bilateral renal length and renal parenchymal area were measured. Pearson and Bland-Altman statistical analyses were used to examine correlations, measurement bias and the degree of agreement between methods.

RESULTS

Renal length measurements in both positions were complete for 201 right and 196 left kidneys. Parenchymal area measurements were complete for both kidneys in 177 children. When compared individually, supine and prone measures of renal length and parenchymal area highly correlated on Pearson analysis (greater than 0.96 and greater than 0.89, respectively). When compared by method, Bland-Altman analyses of differences vs means showed greater than 50% variance, representing wide limits of agreement with poor interrelation. Neither persistent systematic bias nor body habitus influenced results.

CONCLUSIONS

While Pearson analysis showed high correlation for supine and prone renal measurements, Bland-Altman analysis of renal length and parenchymal area demonstrated wide limits of agreement, not allowing interchangeable use of prone and supine measurements. As such, renal ultrasound should specify standardized positions and benchmarks. These results provide guidance to standardize renal ultrasound measurements when renal size is used as an indicator of kidney health.

Sonographic Renal Parenchymal Measurements for the Evaluation and Management of Ureteropelvic Junction Obstruction in Children

PURPOSE

To correlate sonographic renal parenchymal measurements among patients with ureteropelvic junction obstruction (UPJO) labeled society of fetal urology (SFU) hydronephrosis grades 1-4 and to examine whether sonographic renal parenchymal measurements could be used to differentiate conservative vs. surgical management.

MATERIALS AND METHODS

Retrospective chart review and sonographic renal parenchymal measurements (renal length, medullary pyramid thickness, and renal parenchymal thickness) were performed in patients with SFU grades 1-4 hydronephrosis secondary to UPJO managed between 2009 and 2014. Exclusion criteria included other concomitant genitourinary pathology or incomplete follow-up. Anterior-posterior renal pelvic diameter (APRPD) and radionuclide renography were also evaluated when available.

RESULTS

One hundred four patients with UPJO underwent 244 renal and bladder ultrasound (1,464 sonographic renal parenchymal measurements in 488 kidneys). Medullary pyramid thickness and renal parenchymal thickness progressively decreased from SFU grades 1-4 (p < 0.05). A similar trend was appreciated when comparing SFU grades 1 and 2 vs. 3 and 4, as well as SFU grades 3 vs. 4 (p < 0.05). SFU grade 3 and 4 patients who underwent pyeloplasty had longer renal length in comparison to those who were managed conservatively (p < 0.02).

CONCLUSION

This is the first study that evaluates these objective, quantifiable sonographic renal parenchymal measurements in children with unilateral UPJO. These sonographic renal parenchymal measurements correlate closely with worsening of hydronephrosis graded by the SFU and APRPD classification systems. Prospective studies are needed to elucidate the role of sonographic renal parenchymal measurements in the management of children with UPJO.

Comparison of magnetic resonance imaging with radionuclide methods of evaluating the kidney

Nuclear medicine and MRI provide information about renal perfusion, function (glomerular filtration rate), and drainage. Some tracers that are used in nuclear medicine (technetium-diethylene triamine pentaacetic acid ([(99m)Tc-DTPA] and (51)chromium-EDTA) and some contrast media (CM) that are used for MRI (gadolinium-DTPA for instance) share the same pharmacokinetic properties, though, detection techniques are different (low-spatial resolution 2-dimensional projection with a good concentration-to-signal linearity for nuclear medicine and high-resolution 3-dimensional localization with nonlinear behavior for MRI). Thus, though based on the same principles, the methods are not the same and they provide somewhat different information. Many MRI perfusion studies have been conducted; some of them were compared with nuclear medicine with no good agreement. Phase contrast can reliably assess global renal blood flow but not perfusion at a tissular level. Arterial spin labeling has not proven to be a reliable tool to measure renal perfusion. Techniques using CM theoretically can assess perfusion at the tissular level, but they have not proven to be precise. To assess renal function, many models have been proposed. Some MRI techniques using CM, both semiquantitative (Patlak) and quantitative, have shown ability to roughly assess relative function. Some quantitative methods (Annet's and Lee's methods) have even showed that they could roughly estimate absolute renal function, with better results than estimated glomerular filtration rate. Quantification of drainage has not been much studied using MRI.

Automatic measurement of renal volume in children using 99mTc dimercaptosuccinic acid SPECT: normal ranges with body weight

OBJECTIVE

The purpose of this study was to automate volume measurement of pediatric kidneys using Technetium-99m-dimercaptosuccinic acid (99mTc DMSA) SPECT. Assessment of renal size is essential in making an accurate clinical diagnosis and in evaluating normal and abnormal renal growth. Existing techniques for measuring renal length and volume are often observer-dependent and are limited by interobserver variability.

MATERIALS AND METHODS

An automated method using 99mTc DMSA SPECT was developed to measure renal length, volume, and 2D/3D split renal functions. An adaptive threshold was used for segmentation of renal images. To improve measurement accuracy of renal volumes, a boundary-weighted integration and a linear correction from phantom experiments were applied. Using the new automated software, we evaluated 620 normal kidneys in 310 patients aged 1 to 21 years.

RESULTS

In all, 99.4% of renal volume measurement was inter-/intraobserver reproducible without manual intervention. Correlations between renal size (volume and length) and growth parameters (age and body weight) were evaluated by nonlinear regression modeling. Body weight was found to be the best predictor of kidney volume and length (P < 0.0001). Normal ranges were established according to body weight.

CONCLUSIONS

Automatic renal volume measurement with 99mTc DMSA SPECT demonstrates high observer reproducibility, and it is useful for achieving accurate assessment of renal growth using sequential measurements. The renal growth models generated by this study will aid physicians in evaluating and monitoring renal growth.

Measurement of renal dimensions in vivo: A critical appraisal

Kidney volume is regarded as the most precise indicator of kidney size. However, volume assessment is not widely used clinically because its measurement is difficult due to the complex kidney shape. Apart from the conventional methods of measurement of renal dimensions from X-rays, ultrasound scan, computed tomography scan and magnetic resonance imaging have evolved as the three best modalities for this purpose currently. Assessment of kidney size should also be made individually since many factors like body mass index, height, gender, age, position of kidneys, sex, stenoses and number of renal arteries influence the measurements. In this paper, we have critically analysed the advantages and disadvantages of the various methods of renal morphometry, by reviewing the literature spanning over the period of 1976 - 2009.

Radiographic evaluation of children with febrile urinary tract infection: bottom-up, top-down, or none of the above?

The proper algorithm for the radiographic evaluation of children with febrile urinary tract infection (FUTI) is hotly debated. Three studies are commonly administered: renal-bladder ultrasound (RUS), voiding cystourethrogram (VCUG), and dimercapto-succinic acid (DMSA) scan. However, the order in which these tests are obtained depends on the methodology followed: bottom-up or top-down. Each strategy carries advantages and disadvantages, and some groups now advocate even less of a workup (none of the above) due to the current controversies about treatment when abnormalities are diagnosed. New technology is available and still under investigation, but it may help to clarify the interplay between vesicoureteral reflux, renal scarring, and dysfunctional elimination in the future.

Quantitative ultrasound renal parenchymal area correlates with renal volume and identifies reflux nephropathy

PURPOSE

Studies show that renal volume on magnetic resonance imaging correlates with differential function and is decreased in children with vesicoureteral reflux diagnosed after urinary tract infection. We examined the correlation between ultrasound renal parenchymal area and magnetic resonance imaging volume to determine whether quantitative ultrasound renal parenchymal area might be a reliable, less costly and less invasive substitute for renal magnetic resonance imaging volume.

MATERIALS AND METHODS

To determine the correlation of ultrasound renal parenchymal area with magnetic resonance imaging, we identified 82 children with primary vesicoureteral reflux who underwent renal magnetic resonance imaging and ultrasound. Magnetic resonance imaging volume was compared with ultrasound renal parenchymal area, renal length and calculated ellipsoid volume. To determine the correlation of ultrasound renal parenchymal area with reflux grade, ultrasound renal parenchymal area was examined in 96 children with reflux and urinary tract infection, and in 52 with reflux without urinary tract infection. Linear regression and multivariate analysis were performed to find the relationship between ultrasound renal parenchymal area and reflux grade.

RESULTS

The correlation of ultrasound renal parenchymal area with magnetic resonance imaging volume was superior to that of renal length and calculated ellipsoid volume (r(2) = 0.90 vs 0.83 and 0.84, respectively). Hydronephrosis did not affect the correlation. On multiple regression analysis in children with reflux and urinary tract infection higher reflux grade correlated with decreased ultrasound renal parenchymal area (p = 0.0016). In children with reflux without urinary tract infection reflux grade did not correlate with decreased ultrasound renal parenchymal area (p = 0.47).

CONCLUSIONS

Ultrasound renal parenchymal area correlates closely with magnetic resonance imaging derived 3-dimensional renal volume and is capable of detecting progressive renal area loss in patients with reflux and urinary tract infection. More studies are necessary to verify whether data from more invasive tests, such as renal magnetic resonance imaging and dimercapto-succinic acid scan, may be attained from ultrasound renal parenchymal area alone.