Sonographic Evaluation of Hydronephrosis in the Pediatric Population

Transcription

1 ORIGINAL RESEARCH Sonographic Evaluation of Hydronephrosis in the Pediatric Population Is Well-Tempered Sonography Necessary? Marc R. Walker, MD, Sarkis Babikian, MD, Alexander J. Ernest, MD, Troy S. Koch, MD, Michael B. Lustik, MS, Veronica J. Rooks, MD, Leah P. McMann, MD Received March 17, 2014, from the Urology Service, Department of Surgery (M.R.W., A.J.E., L.P.M.), Pediatric Radiology Service, Department of Radiology (S.B., T.S.K., V.J.R.), and Department of Clinical Investigation (M.B.L.), Tripler Army Medical Center, Honolulu, Hawaii USA. Revision requested April 6, Revised manuscript accepted for publication July 2, This work was presented as a podium presentation at the 45th Biannual Meeting of the Society for Fetal Urology; October 2010; San Francisco, California. The views expressed in this article are those of the authors and do not reflect the official policy or position of the Department of the Army, Department of Defense, or the US Government. Address correspondence to Marc R. Walker, MD, Urology Service, Department of Surgery, Tripler Army Medical Center, 1 Jarrett White Rd, Honolulu, HI USA. walkmr@gmail.com Abbreviations IV, intravenous; SFU, Society for Fetal Urology doi: /ultra Objectives Standardized protocols exist for diuretic renography. There are no specific guidelines regarding hydration before renal sonography. This study assessed the importance of the hydration status by sonographic measurements of the anteroposterior diameter and its effect on Society for Fetal Urology (SFU) hydronephrosis grading. Methods Children aged 6 weeks to 16 years (mean age, 22 months) with unilateral SFU grade 3 or 4 hydronephrosis requiring diuretic renal scintigraphy were recruited to undergo prehydration and posthydration renal sonography. Hydrated diuretic renal scintigraphy, or well-tempered renography, was then performed. Renal sonograms were reviewed by a blinded pediatric radiologist and pediatric urologist. Two-sided statistical tests assessed whether SFU grades and the anteroposterior diameter changed significantly after hydration. Results Among 67 kidneys, the pediatric urologist (L.P.M.) and pediatric radiologist (V.J.R.) reported no SFU grade change in 45 (67%) and 52 (78%) kidneys after hydration. In kidneys that changed, the posthydration grade was more likely to be higher. This difference was statistically significant (14 of 22 and 13 of 15 differences were higher grades after hydration for L.P.M. and V.J.R., respectively; P =.06; P =.007). Most kidneys that changed with hydration differed by only 1 SFU grade. Differences greater than 1 grade were seen in 5 control kidneys, which increased from SFU grade 0 to 2. The mean anteroposterior diameter increased significantly between prehydration and posthydration sonography for both hydronephrotic kidneys (1.46 versus 1.72 cm; P <.001) and control kidneys (0.22 versus 0.39 cm; P=.019), but did not correlate with increased SFU grades. Conclusions Hydration does have a substantial effect on the anteroposterior diameter, but it does not correlate with a substantial effect on the SFU grade; therefore, welltempered sonography seems unnecessary. Key Words anteroposterior diameter; hydration; pediatric ultrasound; prenatal hydronephrosis; Society for Fetal Urology grade; sonography The widespread use of prenatal sonography has led to the increased identification of infants with asymptomatic renal pelvic dilatation. There are now established reliable and noninvasive prognostic parameters that are predictive of severe uropathies at the initial evaluation or during follow-up. One parameter used to identify obstruction as the etiology for hydronephrosis is the anteroposterior diameter and its increase on serial renal sonographic examinations in the same patient. Previous studies in 2015 by the American Institute of Ultrasound in Medicine J Ultrasound Med 2015; 34:

2 neonates found that an anteroposterior diameter of greater than 6 mm indicates possible obstruction, and a diameter of greater than 15 mm is highly accurate in identifying infants with severe uropathy (sensitivity and specificity, >90%). 1 5 More recently, Dias et al, 1 followed 371 patients who had prenatal renal pelvic dilatation with serial sonographic examinations every 6 months to clarify the prognostic accuracy of current antenatal hydronephrosis assessment using renal pelvic dilatation. The study concluded that using a combination of prenatal and postnatal anteroposterior diameters, with cutoffs of 16 and 18 mm, respectively, improved the specificity to around 91% for predicting which infants would need further investigation and surgical intervention. 1 Another parameter used to identify clinically important hydronephrosis severity is the Society for Fetal Urology (SFU) hydronephrosis grading system. Founded in 1988, the SFU developed a system to grade hydronephrosis by sonography in an attempt to standardize the interpretation of radiographic tests and the management of infant hydronephrosis by surgery or observation. 6,7 Given that varying the anteroposterior diameter threshold changes the sensitivity and specificity for detecting antenatal hydronephrosis, the SFU hydronephrosis grading system serves as an additional tool for detection of renal disease. 1,2 Society for Fetal Urology grades are scored from 0 through 4 (Figure 1). Grade 0 is no hydronephrosis. Grade 1 involves barely splitting the renal pelvis. Grade 2 involves filling the Figure 1. Society for Fetal Urology grades 0 (A), 1 (B), 2 (C), 3 (D), and 4 (E), as described in the text. A D B E C 656 J Ultrasound Med 2015; 34:

3 intrarenal pelvis or the extrarenal pelvis with dilatation of the major calyces. Grade 3 involves dilatation of minor and major calyces but preservation of the renal parenchyma. Grade 4 is defined as grade 3 with thinning of the renal parenchyma. A recent meta-analysis to determine the outcome of antenatally detected hydronephrosis reported that SFU grade 3 and 4 hydronephrosis resolved or stabilized at a much lower frequency than lesser degrees of hydronephrosis (grades 1 and 2). 8 However, studies have shown that surgical intervention may be needed in some cases of mild hydronephrosis. 9 Children identified as having an increasing anteroposterior diameter on serial renal sonographic examinations or SFU grade 3 or 4 hydronephrosis, in addition to excluding vesicoureteral reflux, subsequently undergo diuretic renal scintigraphy to evaluate for obstructive uropathy. In addition to subjecting the child to radiation, diuretic renal scintigraphy involves intravenous (IV) catheter placement and bladder catheterization. Diuretic renal scintigraphy is performed in the manner of welltempered renography in an effort to minimize the many physiologic factors and technical pitfalls that can introduce variability in the study results. 10 These include bladder catheterization, to counteract the effect of back pressure from a full bladder, and IV hydration with normal saline before scintigraphy. The SFU recognized the potential effect of the hydration status on sonographic evaluations and recommended ad lib fluids orally before and during the study. 6 Oral hydration has been shown to increase renal length in both adults and children. 11,12 However, both studies were performed on normal kidneys in children older than 7 years and adults after oral hydration. Our study evaluated the effect of hydration on abnormal kidneys in infants and children without reflux, with unilateral antenatal hydronephrosis, and with a normal contralateral kidney. Currently, no standardized protocol exists regarding the hydration status at the time renal sonograms are obtained in the evaluation of pediatric hydronephrosis. Furthermore, an increase in the anteroposterior diameter may lead to additional invasive testing, such as diuretic renal scintigraphy, and possibly surgical intervention. We hypothesized that the hydration status at the time sonograms are obtained may influence the measured SFU grade of hydronephrosis and anteroposterior diameter. Koff et al 13 have already shown that the renal pelvis is compliant and enlarges during diuresis in young children with or without hydronephrosis, and this response is exaggerated in children younger than 2 years. They found that diuresis led to an increase in the renal pelvic volume of kidneys that were normal, hydronephrotic kidneys without obstruction, and hydronephrotic, obstructed kidneys. 13 They also found that the degree of the renal pelvic volume increase was greater in the nonobstructed (normal and hydronephrotic) kidneys than in the obstructed kidneys. In their study, Koff et al 13 performed sonographic examinations to determine the renal pelvic volume immediately before and after injection of a diuretic, but they did not evaluate changes in the renal pelvic volume with just hydration alone. Further studies in children and adults evaluating normal kidneys and using hydration alone have also demonstrated a significant increase in renal measurements after hydration. 11,12 Therefore, we hypothesized that the patient s state of hydration is an important factor affecting the outcome of sonography by causing variability in the anteroposterior diameter measurement and assignment of the SFU grade. Diuresis is in part dependent on the availability of fluid within the tissues and vasculature to produce urine and respond to the diuretic stimulus. 10 Whether naturally increasing levels of urine production substantially affect the anteroposterior diameter and SFU grade is unknown at this time. Materials and Methods This study was an Institutional Review Board approved observational prospective controlled trial enrolling infants and children from 1 month to 18 years of age who were previously identified as having unilateral SFU grade 3 or 4 hydronephrosis and were scheduled to have a diuretic renal scintigraphic scan between April 2007 and December All patients had a prior voiding cystourethrogram that excluded reflux. Patients with vesicoureteral reflux, those with previous imaging showing only SFU grade 1 or 2 hydronephrosis, and those whose condition did not warrant diuretic renal scintigraphy were excluded from the study. All parents were urged to withhold food and drink from their children starting 2 hours before the procedure to ensure that all patients presented with a similar level of dehydration. An IV line and Foley catheter were placed by a pediatric nurse as per protocol for a well-tempered renogram. 8 Children 7 years and older who could void on command were allowed to omit the bladder catheter. A renal sonographic examination was then performed (hereafter referred to as prehydration sonography). A standard IV bolus (10 ml/kg over 1 hour) of normal saline was completed. Children without a Foley catheter voided at this time. Another renal sonographic examination was then performed (hereafter referred to as posthydration sonography) as soon as the hydration bolus was completed and once the children J Ultrasound Med 2015; 34:

4 without catheters had voided. The patients then went on to have their renograms. Images of the kidneys were obtained along the major axis (long) and orthogonally at the midpoint of the major axis (transverse) by sonographers. Three different ultrasound machines with 5.0- and 8.0-MHz curvilinear probes were used: iu22 (Philips Healthcare, Bothell, WA), LOGIQ E9 (GE Healthcare, Milwaukee, WI), and Acuson S2000 (Siemens Medical Solutions, Mountain View, CA). The sonographer who performed the prehydration examination also performed the posthydration examination on the same patient. The sonographic studies were then randomly batched into groups of 5 to 10, with patient information and the hydration status hidden. A staff pediatric radiologist (V.J.R.) assigned measurements and SFU grades to each kidney. The cortical thickness was measured in the long axis (Figure 2A), and the anteroposterior diameter was measured in the transverse axis (Figure 2B). Additionally, a staff pediatric urologist (L.P.M.) assigned SFU grades to each kidney independent of V.J.R. and was also blinded to patient information and the hydration status (Table 1). A total of 28 patients (22 boys and 6 girls; age range, 6 weeks 16 years; mean age, 22 months) were enrolled, and all patients were able to complete the study. Due to progression of hydronephrosis during the study period, 4 patients underwent a second renographic examination, and 1 underwent 2 subsequent renographic examinations. The remaining 23 patients underwent only a single renographic examination. Thus, there were 33 usable paired sonograms and 1 unpaired kidney (67 kidneys) for statistical analysis. One kidney was excluded because it was a multicystic dysplastic kidney. For purposes of analysis, clinically important hydronephrosis was defined as SFU grade 3 or higher. There were 33 kidneys that had SFU grade 3 or higher hydronephrosis and 34 control kidneys with clinically unimportant (SFU grade 1 or 2) or no hydronephrosis. One child with previously diagnosed unilateral hydronephrosis had complete resolution, and the sonograms of both kidneys were analyzed in the control group. The SFU grade and anteroposterior diameter were compared on the prehydration and posthydration sonograms for each kidney. Society for Fetal Urology grades were assigned by both the pediatric radiologist (V.J.R.) and the pediatric urologist (L.P.M.), providing 2 complete data sets for evaluation and comparison. The anteroposterior diameter was also measured by the pediatric radiologist. Both were blinded to the hydration status for each kidney. Two-sided statistical tests were done to assess whether SFU grades changed significantly after hydration (Wilcoxon signed rank test) and whether the anteroposterior diameter changed after hydration (paired t test; Table 2). Additionally, κ statistics were calculated to assess the inter-rater reliability of the SFU grading. Figure 2. Cortical thickness measurements (arrows) on the long axis in a hydronephrotic kidney (A) and anteroposterior diameter (arrows) measured orthogonally on a transverse sonogram (B). A B 658 J Ultrasound Med 2015; 34:

5 Results Of the 67 kidneys, L.P.M. reported 45 kidneys (67%) with no change in the SFU grade after hydration. Likewise, V.J.R. reported 52 kidneys (78%) that were unchanged with hydration. In other words, most kidneys did not change in their SFU grade with hydration, irrespective of who assigned the grade. When the SFU grade differed between prehydration and posthydration sonography, the posthydration grade was more likely to be higher than the prehydration grade. This difference was statistically significant (14 of 22 and 13 of 15 differences were higher grades after hydration for L.P.M. and V.J.R., respectively; P =.06; P =.007). Most changes differed by 1 SFU grade at most. The only differences of more than 1 grade were for 5 control kidneys reviewed by L.P.M. that went from SFU grade 0 before hydration to grade 2 after hydration. Only 4 kidneys (3 hydronephrotic and 1 normal) increased from grade 2 to grade 3 when evaluated by L.P.M. (Figure 3). There were no kidneys that changed by more than 1 SFU grade after review by V.J.R., but 1 kidney increased from grade 2 to grade 3 (Figure 4). In no instance did a kidney change from grade 2 hydronephrosis to grade 4 hydronephrosiswith hydration when evaluated by either L.P.M. or V.J.R.. Fernbach et al 6 reported a strong clinical correlation of renal obstruction in SFU grade 3 and 4 kidneys, with sensitivity and specificity of 88% and 95%, respectively. Therefore, the data were dichotomized for evaluation based on clinical importance, with SFU grade 0 through 2 (control) kidneys compared to those with grades of 3 and 4 in a cohort of kidneys without vesicoureteral reflux. Results indicated that when evaluated by L.P.M., 85% of grade 3 and 4 hydronephrotic kidneys and 91% of control kidneys stayed within the same SFU grade in the prehydration to posthydration analysis. When evaluated by V.J.R., the consistency was even higher, with 98% and 100% percent of grade 3 and 4 hydronephrotic and control kidneys maintaining their prehydration SFU grade after hydration, respectively. The anteroposterior diameter showed a statistically significant increase between prehydration and posthydration sonography for both the hydronephrotic kidneys (1.46 versus 1.72 cm; P <.001) and the control kidneys (0.22 versus 0.39 cm; P =.019), but the mean differences of 0.26 and 0.17 cm did not translate to increasing SFU grades (Figure 5). At the time this manuscript was written, 5 of the original 28 patients (4 boys and 1 girl) had progressed to requiring surgery. Four underwent an open pyeloplasty for left ureteropelvic junction obstructions and postoperatively had improvements in drainage. Two of the 4 had decreasing renal function. One had preserved function but borderline hypertension and urinary tract infections. One had increasing pain. All 4 pyeloplasty cases were SFU grade 4 both before and after hydration. One boy had a cutaneous right ureterostomy for congenital megaureter. He had grade 2 hydronephrosis (by both V.J.R. and L.P.M.) without a prehydration to posthydration change. Table 1. Overall Prehydration to Posthydration SFU Grades Assigned by the Pediatric Radiologist (V.J.R.) and Pediatric Urologist (L.P.M.; in Parentheses) Posthydration Prehydration SFU 0 SFU 1 SFU 2 SFU 3 SFU 4 Total SFU 0 12 (17) a 8 (1) b 0 (5) 0 (0) 0 (0) 20 (23) SFU 1 2 (4) c 12 (2) a 4 (2) b 0 (0) 0 (0) 18 (8) SFU 2 0 (0) 0 (0) 16 (5) a 1 (4) b 0 (0) 17 (9) SFU 3 0 (0) 0 (0) 0 (4) c 5 (14) a 0 (2) b 5 (20) SFU 4 0 (0) 0 (0) 0 (0) 0 (0) 7 (7) a 7 (7) Total 14 (21) 20 (3) 20 (16) 6 (18) 7 (9) 67 (67) a No change in grade. b Increase in grade. c Decrease in grade. Table 2. Anteroposterior Diameter Measurements for Hydronephrotic and Control Kidneys Prehydration, cm Posthydration, cm Difference, cm Kidneys n Mean SD Min Max Mean SD Min Max Mean SD Min Max P a Hydronephrotic <.001 Control a Difference between prehydration and posthydration means, paired t test. J Ultrasound Med 2015; 34:

6 Discussion Both prenatal and postnatal hydronephrosis are not uncommon findings, with an estimated incidence of 0.5% to 4.5%, and the clinical course is variable. 3,5,8 Clinicians are constantly challenged to interpret renal studies, which can in turn lead to invasive procedures in an effort to provide renal protection. An estimated 14% to 21% of hydronephrosis is related to obstruction or vesicoureteral reflux, whereas a far greater percentage has no identifiable abnormality. 8 Current literature supports intervention in patients with an anteroposterior diameter of greater than 30 mm, an anteroposterior diameter of greater than 20 mm with calyceal dilation, renal function of less than 30%, worsening renal function, worsening hydronephrosis, or symptoms. 5 However, in the immediate neonatal period, studies have found that the true degree of hydronephrosis is unreliable because of dehydration and low glomerular filtration rates. Those neonates with obstructive uropathy reached their true anteroposterior diameter 1 to 8 weeks after birth. 4 However, even patients with severe hydronephrosis and high SFU grades may stabilize or improve, so serial sonographic evaluations are required to guide treatment decisions. The interpretation and course of antenatal hydro - nephrosis are complicated and more variable than in many other pediatric renal abnormalities. Causes of antenatal hydronephrosis include obstructive and nonobstructive etiologies as well as vesicoureteral reflux. 4 These patients are routinely followed with measurements of the anteroposterior diameter and SFU grades on renal sonography, although there is no standardized protocol. 2 On the basis of radiographic findings, postnatal patients may warrant surgical intervention. Therefore, it is paramount, for prognosis and treatment discussions, that the radiographic imaging is both accurate and consistent. 7 It is also important to note that even the SFU has acknowledged that its rating mechanism has good intra-rater reliability but only modest inter-rater reliability. 2 Radiographic consistency in the evaluation of a dynamic structure such as the renal pelvis is difficult to ensure. Historically, similar questions have been raised about ensuring diagnostic accuracy of other imaging studies. One example is the evaluation of renal obstruction by diuretic renal scintigraphy, which is an imaging modality whereby an IV isotope is injected and renal uptake, excretion, and elimination from the collecting system are followed after the injection of a diuretic. This study is an excellent evaluation of the function and drainage of the collecting system. However, evaluations using diuretic renal scintigraphy are subject to many confounders, which include renal maturity, renal pelvic volume, retrograde vesical pressures, pelvic compliance, and distensibility. 13 In an attempt to minimize the physiologic confounders to improve consistency and accuracy, the well-tempered renogram was developed. 10 These same physiologic confounders have the potential to affect the evaluation of pediatric patients who are followed with surveillance sonography for hydronephrosis. Considering the dynamic, distensible Figure 3. Prehydration to posthydration changes of the SFU grade in 67 kidneys evaluated by the pediatric urologist (L.P.M.). Figure 4. Prehydration to posthydration changes of the SFU grade in 67 kidneys evaluated by the pediatric radiologist (V.J.R.). Figure 5. Mean anteroposterior diameter (APD) in hydronephrotic and control kidneys before and after a fluid bolus. 660 J Ultrasound Med 2015; 34:

7 nature of the collecting system and the direct relationship between hydration and urine production, one physiologic confounder is the hydration status. With other confounders minimized, this study indicates that the anatomic variation in the anteroposterior diameter due to the hydration status alone averages less than 2.5 mm on renal sonography. The increase in the anteroposterior diameter confirms that the saline bolus was enough to increase urine production. However, the change in the anteroposterior diameter failed to increase SFU grades from grades 0 through 2 to grades 3 and 4. The minor grade changes within the cohort with SFU grades 0 through 2 would likely not result in a need for surgical intervention. This study also allowed for a comparison of the interrater reliability between a fellowship-trained pediatric radiologist and fellowship-trained pediatric urologist. Both remained consistent in their own scoring, which is consistent with the acknowledgments made by the SFU regarding intra-rater reliability. 2 Overall, the pediatric urologist generally assigned slightly higher SFU scores. Most of the variation came in the lower grades (0 2) and the κ values still indicated fair to moderate agreement between the raters (κ = for the hydronephrotic and control kidneys before and after hydration). This variability was not unexpected, as SFU scoring is a moderately subjective radiographic interpretation of renal pelvis dilatation. The radiologist was also tasked with providing renal measurements (anteroposterior diameter) as well as parenchymal thickness measurements and had more objective data as a basis for SFU scoring. These additional data were unavailable to the blinded pediatric urologist. During the study, patients needing additional diuretic renal scintigraphy for progression of hydronephrosis were allowed to participate more than once as individual study participants. During the final analysis, 11 studies were linked to 5 patients. The time between studies in individual patients ranged from 3 to 18 months. These patients provided additional data points, and since the prehydration and posthydration kidneys served as their own controls, the varying degrees of chronologic separation did not affect the overall analysis. Re-enrollment also provided internal confirmation that the protocol remained consistent according to parental feedback. We acknowledge that our study had limitations. Minor confounders were identified, which were difficult to eliminate. One such confounder was the variability in sonographer imaging practices. Although the same sonographer was assigned to perform the prehydration and posthydration imaging for each patient, in 3 patients, the sonographer changed between prehydration and posthydration examinations. The sonographers were also encouraged to take only enough images sufficient to make the required calculations on posthydration imaging. However, there was still some variation in the total number of images per study. There were no studies that required additional imaging to assign SFU grades or measure the anteroposterior diameter. Another confounder identified before the study began was the overall hydration status of the children before presentation. Parents were instructed not to allow the child to eat or drink for at least 2 hours before the study, but based on the timing of the studies, some patients had not taken anything by mouth since the night before, and others would have eaten and drunk until the 2-hour cutoff. It is reasonable to speculate that the effect of a hydration bolus may be dampened in a child who has fasted overnight versus a child who had taken food or drink by mouth only 2 hours before. However, previous studies on patients who fasted for as long as 10 hours before surgery have concluded that the intravascular volume in a healthy patient remains constant. 14 Therefore, the varying degrees of fasting would not substantially change the patients responses to the fluid bolus. Despite limitations, this observational prospective controlled trial aimed to minimize confounders based on the principles of a well-tempered renogram. This design allowed isolation of the hydration status as the primary variable and provided substantial evidence against hydration as a confounding factor in renal sonography of hydro - nephrotic kidneys in children. Additional studies with larger patient numbers are needed to validate our findings. In conclusion, physiologic changes to the renal pelvis after a standard IV hydration bolus do have a statistically significant effect on the anteroposterior diameter in children being evaluated for hydronephrosis, but this effect did not translate into an increase from an SFU grade of 0 through 2 to a higher SFU grade of 3 or 4. Therefore, since hydration did not change the SFU grade in most kidneys, performance of a well-tempered sonographic examination seems unnecessary. References 1. Dias CS, Silva JMP, Pereira AK, et al. Diagnostic accuracy of renal pelvic dilatation for detecting surgically managed ureteropelvic junction obstruction. J Urol 2013; 190: Nguyen HT, Herndon CD, Cooper C, et al. The Society for Fetal Urology consensus statement on the evaluation and management of antenatal hydronephrosis. J Pediatr Urol 2010; 6: J Ultrasound Med 2015; 34:

8 3. Bouzada MC, Oliveira EA, Pereira AK, et al. Diagnostic accuracy of postnatal renal pelvic diameter as a predictor of uropathy: a prospective study. Pediatr Radiol 2004; 34: Clautice-Engle T, Anderson NG, Allan RB, Abbott GD. Diagnosis of obstructive hydronephrosis in infants: comparison sonograms performed 6 days and 6 weeks after birth. AJR Am J Roentgenol 1995; 164: Yiee J, Wilcox D. Management of fetal hydronephrosis. Pediatr Nephrol 2008; 23: Fernbach SK, Maizels M, Conway JJ. Ultrasound grading of hydronephrosis: introduction to the system used by the Society for Fetal Urology. Pediatr Radiol 1993; 23: Maizels M, Mitchell B, Kass, E, Fernbach SK, Conway JJ. Outcome of nonspecific hydronephrosis in the infant: a report from the Registry of the Society for Fetal Urology. J Urol 1994; 152: Sidhu G, Beyene J, Rosenblum ND. Outcome of isolated antenatal hydronephrosis: a systematic review and meta-analysis. Pediatr Nephrol 2006; 21: Noe HN, Magill LL. Progression of mild ureteropelvic junction obstruction in infancy. Urology 1987; 30: Conway JJ. Well-tempered diuresis renography: its historical development, physiological and technical pitfalls, and standardized technique protocol. Semin Nucl Med 1992; 22: Kantarci F, Mihmanli I, Adaleti I, et al. The effect of fluid intake on renal length measurements in adults. J Clin Ultrasound 2006; 34: Peerboccus M, Darmy N, Pather S, Devriendt A, Avni F. The impact of hydration on renal measurements and on cortical echogenicity in children. Pediatr Radiol 2013; 43: Koff SA, Binkovitz L, Coley B, Jayanthi VR. Renal pelvis volume during diuresis in children with hydronephrosis: implications for diagnosing obstruction with diuretic renography. J Urol 2005; 174: Jacob M, Chappell D, Conzen P, Finsterer U, Rehm M. Blood volume is normal after pre-operative overnight fasting. Acta Anaesthesiol Scand 2008; 52: J Ultrasound Med 2015; 34: