- Email: [email protected]
Predictive Value of Decreased Renal Pelvis Anteroposterior Diameter in Prone Position for Prenatally Detected Hydronephrosis
Predictive Value of Decreased Renal Pelvis Anteroposterior Diameter in Prone Position for Prenatally Detected Hydronephrosis Gyanendra Sharma,* Anshu Sharma and Pankaj Maheshwari From the Chitale Clinic Private Limited, Solapur (GS, AS), and Aditya Birla Hospital, Pune (PM), Maharashtra, India
Purpose: It is important to differentiate between those cases of prenatally detected hydronephrosis that are significant and those that are likely to resolve spontaneously. We evaluated the anteroposterior pelvic diameter of the renal pelvis postnatally in the supine and prone positions, and determined whether the difference between these 2 positions helps predict the outcome of prenatally detected hydronephrosis. Materials and Methods: From May 2009 to June 2011, 38 infants with prenatally detected unilateral ureteropelvic junction type hydronephrosis were evaluated. The anteroposterior pelvic diameter was noted in the supine and prone positions. Functional evaluation was done by radionuclide renogram. Those with a split function of less than 40% underwent pyeloplasty. All other patients were followed by serial ultrasound examination. Results: Six infants had an anteroposterior pelvic diameter larger than 40 mm with no change in diameter in the supine vs prone positions. Seven of 16 infants with an anteroposterior pelvic diameter between 30 and 40 mm, and 11 of 15 infants with an anteroposterior pelvic diameter between 15 and 30 mm had a smaller anteroposterior pelvic diameter in the prone position. These infants had normal renal function, improvement in hydronephrosis and did not need pyeloplasty. All the infants with no change in anteroposterior pelvic diameter in either position had poorer renal function, necessitating pyeloplasty. Conclusions: Those cases of prenatally detected ureteropelvic junction type of hydronephrosis in which the anteroposterior pelvic diameter is smaller in the prone position than in the supine position showed improvement in hydronephrosis, while those with no change in anteroposterior pelvic diameter had worsening of hydronephrosis and needed surgical intervention.
Abbreviations and Acronyms APPD ⫽ anteroposterior pelvic diameter UPJ ⫽ ureteropelvic junction Submitted for publication August 24, 2011. * Correspondence: Chitale Clinic Pvt. Ltd., 165 D Railway Lines, Solapur– 413001, Maharashtra, India (telephone: 91 217 2319251 or 91217 2319252; FAX: 91 2172319253; Mobile: 91 9822195058; e-mail: [email protected]).
See Editorial on page 1535.
Key Words: hydronephrosis, prenatal diagnosis, ultrasonography, postnatal care, multicystic renal dysplasia THE detection of renal abnormalities with prenatal ultrasonography was first reported in the 1970s.1 Hydronephrosis is one of the most commonly detected anomalies, affecting 1% to 5% of all pregnancies.2 A newborn with prenatal hydronephrosis should undergo a thorough postnatal evaluation of the upper and lower tracts be-
cause 12% to 88% of these children will have demonstrable pathology depending on the degree of prenatally detected hydronephrosis.3,4 The most common etiology for prenatal hydronephrosis is transient or nonobstructive hydronephrosis.5 Following the detection of hydronephrosis by ultrasonography, grading was performed
0022-5347/12/1875-1839/0 THE JOURNAL OF UROLOGY® © 2012 by AMERICAN UROLOGICAL ASSOCIATION EDUCATION
Vol. 187, 1839-1843, May 2012 Printed in U.S.A. DOI:10.1016/j.juro.2011.12.093
AND
RESEARCH, INC.
www.jurology.com
1839
1840
ANTEROPOSTERIOR DIAMETER OF RENAL PELVIS IN SUPINE AND PRONE POSITIONS
using various parameters. The anteroposterior pelvic diameter and Society for Fetal Urology grading are commonly used to describe the severity of hydronephrosis.6 –9 Ureteropelvic junction obstruction is the most common cause of significant dilatation of the collecting system in the fetal kidney.10 The current problem is that the diagnosis of UPJ is made at the time of prenatal ultrasonography. Thus, parents are often apprehensive that the fetus will need surgical intervention as a newborn.11 Because not all cases of prenatally detected hydronephrosis need surgery, it is of the utmost importance to differentiate between an abnormality that is clinically important from the less important physiological dilatations.3 This distinction can only be achieved by assessing the postnatal outcome of prenatally detected hydronephrosis. Dhillon followed a cohort of children with hydronephrosis due to presumed UPJ obstruction and used the APPD to predict the need for surgery.12 In this study we evaluated the APPD in the transverse plane in the supine and prone positions in newborns and infants with prenatally detected hydronephrosis, and determined whether the difference in APPD between these 2 positions helped predict the outcome of hydronephrosis.
MATERIALS AND METHODS A total of 54 newborns and infants presenting with prenatally detected hydronephrosis suggestive of UPJ obstruction were evaluated from May 2009 to June 2011 in this prospective study. As we do not have an institutional review board, the consent of the management of the hospital was taken. Nine patients were excluded from study because they had vesicoureteral reflux, bilateral hydronephrosis or hydroureter, or other associated anomalies. Seven patients who were lost to followup were also excluded from analysis. All patients were evaluated by ultrasonography at initial presentation and evaluated serially afterward at regular intervals. During the entire study period ultrasonography was performed by the same sonologist (AS) to avoid bias. The ultrasound machine, probe and settings were kept identical during initial and followup scans to reduce error. The hydration status of the infants can be variable and can affect the anteroposterior diameter measurement. Therefore, the mother was asked to feed the baby adequately before coming for ultrasound examination. The infants were examined after they had voided because a full bladder can affect the APPD measurement and impair drainage of urine from the kidneys into the bladder. The APPD was measured at the level of renal hilum initially in the transverse plane with the infant in supine position (with the ultrasound probe placed laterally in the midaxillary line). Then the infant was made prone and the APPD measured at the level of renal hilum in the transverse plane. Patients with an APPD larger than 30 mm in the supine position were followed monthly. Those with an
APPD between 15 and 30 mm were followed bimonthly and those with an APPD smaller than 15 mm were followed every 3 months. During each visit the APPD was measured in the supine and prone positions, and features of worsening hydronephrosis like increase in APPD, calyceal dilatation and parenchymal thinning were noted. Of the 38 patients who completed the study 2 newborns were evaluated on days 5 to 7 after birth. There were 15 infants first evaluated between 4 and 6 weeks after birth, and 21 who were first evaluated between 2 and 3 months after birth. Initial radionuclide scans were done between 4 and 6 weeks. In those 21 infants who were initially seen between 2 and 3 months the radionuclide scan was done at that time. Renogram was repeated in those children who showed worsening of hydronephrosis on followup ultrasounds. Indication for pyeloplasty was reduced function (less than 40%) at the first renogram or later. Patients with increasing hydronephrosis and/or calyceal dilatation and/ or parenchymal thinning on followup ultrasounds were evaluated by a second renogram. Pyeloplasty was performed in patients with reduced function (less than 40%) at the first renogram or on later followup. The end point of the study was performance of pyeloplasty or reduction of renal pelvic size to less than 7 mm. The results were tested using the Wilcoxon signed rank sum test for the difference in APPD between the supine and the prone position. The relationship between lack of change in APPD and the need for pyeloplasty was tested using the chi-square test. Both statistical tests were performed at a 5% level of significance.
RESULTS There were 30 males and 8 females in the study group. Left side UPJ type hydronephrosis was seen in 27 patients and right side hydronephrosis was seen in 11. The numbers of patients with APPD in the supine and prone positions are shown in tables 1 and 2. Six patients had an APPD larger than 40 mm, and none showed any change in diameter in the supine vs prone position. In the group with APPD between 30 and 40 mm, 7 children had an APPD that was smaller in the prone than in the supine position. Of the 15 children with APPD between 15 and 30 mm in the supine position 11 had a smaller
Table 1. No. Need for Pyeloplasty due to Renal Function Less Than 40% on Renogram
APPD Subsets in Supine Position
Total No./ Subset
No. No Change in APPD in Prone Position
Greater than 50 mm 40–50 mm 30–40 mm 15–30 mm Less than 15 mm
2 4 16 15 1
2 4 9 4 0
2 4 9 4 0
38
19
19
Totals
ANTEROPOSTERIOR DIAMETER OF RENAL PELVIS IN SUPINE AND PRONE POSITIONS
Table 2. APPD Subsets in Supine Position
Total No./ Subset
No. With Decrease Greater Than 10% of APPD in Prone Position
Greater than 50 mm 40–50 mm 30–40 mm 15–30 mm Less than 15 mm
2 4 16 15 1
0 0 7 11 1
38
19
Totals
None of the patients who had a decrease in APPD of greater than 10% in the prone position had deterioration of renal function on renogram and therefore, did not need pyeloplasty.
APPD in the prone position. These children had a greater than 10% decrease in APPD in the prone position. The only child in this study with an APPD smaller than 15 mm also showed a decrease in APPD in the prone position. The need for surgical intervention based on the differential function in the renogram of these children was studied. All children who had a decrease in APPD in the prone vs supine position had well preserved renal function. In addition, on serial followup ultrasounds they showed improvement with a progressive decrease in hydronephrosis. Of the 19 patients with no change in APPD in the supine and prone position there were 14 whose initial radionuclide study showed that the hydronephrotic kidney had a differential function of less than 40%. These cases were treated with pyeloplasty. There were 5 patients who showed no change in APPD in both positions. They had well preserved renal function during the initial renogram at 6 weeks (function of hydronephrotic kidney greater than 40%) and they were kept under observation. During the ultrasound examination done during followup there was an increase in the APPD with no change in the supine and prone positions, and worsening of hydronephrosis. Repeat renogram 3 to 6 months after the initial renogram in these 5 patients showed the hydronephrotic kidney had poorer function (less than 40%). Therefore, these 5 patients were treated with pyeloplasty.
DISCUSSION Prenatal detection of hydronephrosis has led us to a scenario in which the patient is presenting to the urologist before the baby is even born with a presumptive diagnosis rather than a symptom.13 In most cases the etiology of prenatal hydronephrosis is transient or physiological, has no clinical significance and is likely to resolve at the end of pregnancy or within the first year of life.14,15 In other cases prenatal hydronephrosis is associated with clinically important urological conditions. The dilemma then
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arises of how to differentiate clinically significant hydronephrosis from that which may resolve spontaneously. A common cause of newborn hydronephrosis is UPJ obstruction. Management of UPJ obstruction has triggered considerable debate, with some centers advocating early intervention while others recommend a more conservative approach.16 Ultrasonography and radionuclide renography are widely used to identify those patients who require pyeloplasty.9 The Great Ormond Street group has used anteroposterior pelvic diameter for assessment. They recommended simple followup for pelvic dilatations smaller than 12 mm and surgery for those larger than 50 mm. They also found that of those cases with an APPD larger than 40 mm, 80% needed surgery, while 55% of those with an APPD larger than 30 mm needed pyeloplasty.12,17 Onen reported that neither Society for Fetal Urology grading nor anteroposterior pelvic diameter could determine the severity of hydronephrosis, and he proposed an alternative grading system.7 Other investigators have used renal parenchymal area, calyx-to-parenchymal ratio and pelvis cortex ratio as a sonographic marker of UPJ obstruction.9 These various parameters have been evaluated to address the crucial decision in the management of unilateral UPJ obstruction of whether to intervene. Although the radionuclide renogram is a gold standard, the drainage curves from the initial renogram are not predictive of those requiring surgical intervention for UPJ obstruction.18 In our study the anteroposterior diameter of the renal pelvis was determined in the transverse plane in the supine and prone positions. This study started with a chance observation of one of the investigators (AS) that the APPD of one of the newborns was smaller in the prone than in the supine position. Subsequently all the children who presented to our center with a diagnosis of prenatally detected hydronephrosis were studied with APPD measured in the supine and prone position. In our study of 38 patients 30 were male and 27 had hydronephrosis on the left side. The preponderance of prenatal hydronephrosis in males and the dominance on the left side is well documented in the literature, although the side of kidney involvement does not determine the clinical outcome.19 There were 6 patients with an APPD larger than 40 mm and none showed any change in the prone position. The differential renal function on the renogram showed the hydronephrotic kidney had poorer function than the other normal kidney, and all these patients needed pyeloplasty. In the group of 16 children with an APPD between 30 and 40 mm in the supine position on the initial evaluation 7 had a difference of more than 10% in APPD measured in the supine and prone positions, with the diameter in the prone position
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ANTEROPOSTERIOR DIAMETER OF RENAL PELVIS IN SUPINE AND PRONE POSITIONS
smaller by at least 10% compared to the supine position (see figure). In addition, the initial renogram did not show much difference in the function of the renal units. On serial followup ultrasonography there was a decrease in the APPD in the prone and supine positions. The 9 patients in this group with no difference in the APPD in the prone and supine positions on initial ultrasound examination showed poor function of the hydronephrotic kidney on radionuclide renogram (6 immediate and 3 on followup), necessitating pyeloplasty. In the group with an APPD between 15 and 30 mm on initial evaluation 11 children had a smaller APPD in the prone than in the supine position. All showed normal function on renogram. Ultrasound evaluation during followup showed a decrease in the APPD in the supine and prone positions. By 1 year the APPD was 7 mm or smaller in these children. The 5 patients who showed no change in APPD in the supine and prone positions (3 in the 30 to 40 mm and 2 in the 15 to 30 mm group) had well preserved renal function on the renogram done at age 6 weeks. Ultrasound examinations on followup showed an increase in APPD with no change in the supine and prone positions. Repeat renogram demonstrated poor function of the hydronephrotic kidney, necessitating pyeloplasty. Thus, this study puts forth an interesting finding. If the initial postnatal ultrasound examination shows a decrease in the APPD in the prone vs supine position with the difference being greater than 10%, then these kidneys showed spontaneous resolution of or improvement in hydronephrosis and had well preserved renal function. Those patients with no change in APPD in the supine and prone positions had deterioration of renal function and needed surgical intervention (chi-square test p ⬍0.001).
The rationale for the smaller APPD in the prone position in cases which showed improvement and eventual resolution of hydronephrosis is easy to understand from the prone films taken during excretory urography. Prone positioning enhances the drainage of the renal pelvis and the collecting system empties rapidly in the ureters. Thus, the prone film of excretory urography is excellent for ureteral filling. In the prone position the lower pole of the kidney and the proximal end of the ureter are placed more anteriorly than the upper pole of the kidney. The pelvis also falls anterior to the psoas muscle. The pelvis and upper ureter fill more rapidly in prone position.20 –22 Thus, the nonobstructive dilated pelvis would drain better in the prone position and would have an APPD smaller than that in the supine position. Obstructed systems would not drain better in the prone position and, thus, the APPD in the supine and prone positions in these systems would be similar. A shortcoming of this study is the relatively small number of patients. However, the findings are important because the postnatal ultrasound can predict the possibility of resolution of prenatally detected hydronephrosis as well as identify that subset of patients for whom there is less chance of improvement of hydronephrosis. Identifying the latter subset of patients is imperative because waiting for a longer period by keeping them under observation can prove harmful to the renal parenchyma. Ransley et al have shown that kidneys with relative renal function as high as 40% can deteriorate during periods of observation.17 Following surgical relief of obstruction the relative renal function does not always return to the pre-deterioration levels. Postnatal sonographic measurement of APPD in the supine and prone positions can differentiate those newborns who will have improvement of hydronephrosis from those who are less likely to show such improvement. This can serve as a guide to determine the need for intervention before irreversible damage sets in.
CONCLUSIONS
Figure.
The dilemma in the management of prenatally detected hydronephrosis is to differentiate clinically significant hydronephrosis from that which may resolve spontaneously. Despite varying opinions regarding the management of prenatal hydronephrosis, the trend is toward a conservative approach.5 Of course, this should not be at the cost of increased risk of renal damage. In this study we propose simple bedside ultrasonography as a useful, noninvasive modality to identify kidneys at risk for damage and/or deterioration with time. Those cases with prenatally detected UPJ type of hydronephrosis and
ANTEROPOSTERIOR DIAMETER OF RENAL PELVIS IN SUPINE AND PRONE POSITIONS
an APPD smaller in the prone than in the supine position on postnatal evaluation show improvement in hydronephrosis on followup, whereas those cases in which there is no change in APPD in the supine and prone positions are at increased risk for damage. Thus, ultrasonography done in the prone and supine positions can help to differentiate nonob-
1843
structive dilatation from clinically significant obstructive dilatation. These findings in a small number of patients, if substantiated further by a larger multicenter study encompassing a larger patient pool, would definitely confirm that the first postnatal evaluation by ultrasonography is of immense predictive value in the treatment of these patients.
REFERENCES 1. Garrett WJ, Grunwald G and Robinson DE: Prenatal diagnosis of fetal polycystic kidney by ultrasound. Aust N Z J Obstet Gynaecol 1970; 10: 7.
8. Rodriguez LV, Lock J, Kennedy WA et al: Evaluation of sonographic renal parenchymal area in the management of hydronephrosis. J Urol 2001; 165: 548.
2. 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: 212.
9. Babu R and Sai V: Pelvis/cortex ratio: a sonographic marker of pelvi ureteric junction obstruction in children. Indian J Urol 2010; 26: 494.
3. Lee RS, Cendron M, Kinnamon DD et al: Antenatal hydronephrosis as a predictor of postnatal outcome: a meta-analysis. Pediatrics 2006; 118: 586. 4. Kitchens DM and Herndon CD: Antenatal hydronephrosis. Curr Urol Rep 2009; 10: 126. 5. Passerotti CC, Kalish LA, Chow J et al: The predictive value of the first postnatal ultrasound in children with antenatal hydronephrosis. J Pediatr Urol 2011; 7: 128. 6. Onen A, Jayanthi VR and Koff SA: Long-term followup of prenatally detected severe bilateral newborn hydronephrosis initially managed nonoperatively. J Urol 2002; 168: 1118. 7. Onen A: An alternative grading system to refine the criteria for severity of hydronephrosis and optimal treatment guidelines in neonates with primary UPJ-type hydronephrosis. J Pediatr Urol 2007; 3: 200.
10. Carr M and El-Ghoneimi A: Anomalies and surgery of the ureteropelvic junction in children. In: Campbell-Walsh Urology, 9th ed. Edited by AJ Wein, LR Kavoussi, AC Novick et al. Philadelphia: Saunders Elsevier 2007; pp 3359 –3380. 11. Harding LJ, Malone PS and Wellesley DG: Antenatal minimal hydronephrosis: is its follow-up an unnecessary cause of concern? Prenat Diagn 1999; 19: 701. 12. Dhillon HK: Prenatally diagnosed hydronephrosis: the Great Ormond Street experience. Br J Urol 1998; 81: 39. 13. Ismaili K, Hall M, Piepsz A et al: Insights into the pathogenesis and natural history of fetuses with renal pelvis dilatation. Eur Urol 2005; 48: 207. 14. Woodward M and Frank D: Postnatal management of antenatal hydronephrosis. BJU Int 2002; 89: 149. 15. Sairam S, Al-Habib A, Sasson S et al: Natural history of fetal hydronephrosis diagnosed on mid-
trimester ultrasound. Ultrasound Obstet Gynecol 2001; 17: 191. 16. Koff SA: Postnatal management of antenatal hydronephrosis using an observational approach. Urology 2000; 55: 609. 17. Ransley PG, Dhillon HK, Gordon I et al: The postnatal management of hydronephrosis diagnosed by prenatal ultrasound. J Urol 1990; 144: 584. 18. Hafez AT, McLorie G, Bagli D et al: Analysis of trends on serial ultrasound for high grade neonatal hydronephrosis. J Urol 2002; 168: 1518. 19. Cheng AM, Phan V, Geary DF et al: Outcome of isolated antenatal hydronephrosis. Arch Pediatr Adolesc Med 2004; 158: 38. 20. Friedenberg RM and Harris RD: Excretory urography in the adult. In: Clinical Urography, 2nd ed. Edited by HM Pollack. Philadelphia: WB Saunders 2000; pp 147–257. 21. Carrico CW and Zerin JM: Sonographic measurement of renal length in children: does the position of the patient matter? Pediatr Radiol 1996; 26: 553. 22. Berdon WE, Baker DH and Leonidas J: Advantages of prone positioning in gastrointestinal and genitourinary roentgenologic studies in infants and children. Am J Roentgenol Radium Ther Nucl Med 1968; 103: 444.
Purpose: It is important to differentiate between those cases of prenatally detected hydronephrosis that are significant and those that are likely to resolve spontaneously. We evaluated the anteroposterior pelvic diameter of the renal pelvis postnatally in the supine and prone positions, and determined whether the difference between these 2 positions helps predict the outcome of prenatally detected hydronephrosis. Materials and Methods: From May 2009 to June 2011, 38 infants with prenatally detected unilateral ureteropelvic junction type hydronephrosis were evaluated. The anteroposterior pelvic diameter was noted in the supine and prone positions. Functional evaluation was done by radionuclide renogram. Those with a split function of less than 40% underwent pyeloplasty. All other patients were followed by serial ultrasound examination. Results: Six infants had an anteroposterior pelvic diameter larger than 40 mm with no change in diameter in the supine vs prone positions. Seven of 16 infants with an anteroposterior pelvic diameter between 30 and 40 mm, and 11 of 15 infants with an anteroposterior pelvic diameter between 15 and 30 mm had a smaller anteroposterior pelvic diameter in the prone position. These infants had normal renal function, improvement in hydronephrosis and did not need pyeloplasty. All the infants with no change in anteroposterior pelvic diameter in either position had poorer renal function, necessitating pyeloplasty. Conclusions: Those cases of prenatally detected ureteropelvic junction type of hydronephrosis in which the anteroposterior pelvic diameter is smaller in the prone position than in the supine position showed improvement in hydronephrosis, while those with no change in anteroposterior pelvic diameter had worsening of hydronephrosis and needed surgical intervention.
Abbreviations and Acronyms APPD ⫽ anteroposterior pelvic diameter UPJ ⫽ ureteropelvic junction Submitted for publication August 24, 2011. * Correspondence: Chitale Clinic Pvt. Ltd., 165 D Railway Lines, Solapur– 413001, Maharashtra, India (telephone: 91 217 2319251 or 91217 2319252; FAX: 91 2172319253; Mobile: 91 9822195058; e-mail: [email protected]).
See Editorial on page 1535.
Key Words: hydronephrosis, prenatal diagnosis, ultrasonography, postnatal care, multicystic renal dysplasia THE detection of renal abnormalities with prenatal ultrasonography was first reported in the 1970s.1 Hydronephrosis is one of the most commonly detected anomalies, affecting 1% to 5% of all pregnancies.2 A newborn with prenatal hydronephrosis should undergo a thorough postnatal evaluation of the upper and lower tracts be-
cause 12% to 88% of these children will have demonstrable pathology depending on the degree of prenatally detected hydronephrosis.3,4 The most common etiology for prenatal hydronephrosis is transient or nonobstructive hydronephrosis.5 Following the detection of hydronephrosis by ultrasonography, grading was performed
0022-5347/12/1875-1839/0 THE JOURNAL OF UROLOGY® © 2012 by AMERICAN UROLOGICAL ASSOCIATION EDUCATION
Vol. 187, 1839-1843, May 2012 Printed in U.S.A. DOI:10.1016/j.juro.2011.12.093
AND
RESEARCH, INC.
www.jurology.com
1839
1840
ANTEROPOSTERIOR DIAMETER OF RENAL PELVIS IN SUPINE AND PRONE POSITIONS
using various parameters. The anteroposterior pelvic diameter and Society for Fetal Urology grading are commonly used to describe the severity of hydronephrosis.6 –9 Ureteropelvic junction obstruction is the most common cause of significant dilatation of the collecting system in the fetal kidney.10 The current problem is that the diagnosis of UPJ is made at the time of prenatal ultrasonography. Thus, parents are often apprehensive that the fetus will need surgical intervention as a newborn.11 Because not all cases of prenatally detected hydronephrosis need surgery, it is of the utmost importance to differentiate between an abnormality that is clinically important from the less important physiological dilatations.3 This distinction can only be achieved by assessing the postnatal outcome of prenatally detected hydronephrosis. Dhillon followed a cohort of children with hydronephrosis due to presumed UPJ obstruction and used the APPD to predict the need for surgery.12 In this study we evaluated the APPD in the transverse plane in the supine and prone positions in newborns and infants with prenatally detected hydronephrosis, and determined whether the difference in APPD between these 2 positions helped predict the outcome of hydronephrosis.
MATERIALS AND METHODS A total of 54 newborns and infants presenting with prenatally detected hydronephrosis suggestive of UPJ obstruction were evaluated from May 2009 to June 2011 in this prospective study. As we do not have an institutional review board, the consent of the management of the hospital was taken. Nine patients were excluded from study because they had vesicoureteral reflux, bilateral hydronephrosis or hydroureter, or other associated anomalies. Seven patients who were lost to followup were also excluded from analysis. All patients were evaluated by ultrasonography at initial presentation and evaluated serially afterward at regular intervals. During the entire study period ultrasonography was performed by the same sonologist (AS) to avoid bias. The ultrasound machine, probe and settings were kept identical during initial and followup scans to reduce error. The hydration status of the infants can be variable and can affect the anteroposterior diameter measurement. Therefore, the mother was asked to feed the baby adequately before coming for ultrasound examination. The infants were examined after they had voided because a full bladder can affect the APPD measurement and impair drainage of urine from the kidneys into the bladder. The APPD was measured at the level of renal hilum initially in the transverse plane with the infant in supine position (with the ultrasound probe placed laterally in the midaxillary line). Then the infant was made prone and the APPD measured at the level of renal hilum in the transverse plane. Patients with an APPD larger than 30 mm in the supine position were followed monthly. Those with an
APPD between 15 and 30 mm were followed bimonthly and those with an APPD smaller than 15 mm were followed every 3 months. During each visit the APPD was measured in the supine and prone positions, and features of worsening hydronephrosis like increase in APPD, calyceal dilatation and parenchymal thinning were noted. Of the 38 patients who completed the study 2 newborns were evaluated on days 5 to 7 after birth. There were 15 infants first evaluated between 4 and 6 weeks after birth, and 21 who were first evaluated between 2 and 3 months after birth. Initial radionuclide scans were done between 4 and 6 weeks. In those 21 infants who were initially seen between 2 and 3 months the radionuclide scan was done at that time. Renogram was repeated in those children who showed worsening of hydronephrosis on followup ultrasounds. Indication for pyeloplasty was reduced function (less than 40%) at the first renogram or later. Patients with increasing hydronephrosis and/or calyceal dilatation and/ or parenchymal thinning on followup ultrasounds were evaluated by a second renogram. Pyeloplasty was performed in patients with reduced function (less than 40%) at the first renogram or on later followup. The end point of the study was performance of pyeloplasty or reduction of renal pelvic size to less than 7 mm. The results were tested using the Wilcoxon signed rank sum test for the difference in APPD between the supine and the prone position. The relationship between lack of change in APPD and the need for pyeloplasty was tested using the chi-square test. Both statistical tests were performed at a 5% level of significance.
RESULTS There were 30 males and 8 females in the study group. Left side UPJ type hydronephrosis was seen in 27 patients and right side hydronephrosis was seen in 11. The numbers of patients with APPD in the supine and prone positions are shown in tables 1 and 2. Six patients had an APPD larger than 40 mm, and none showed any change in diameter in the supine vs prone position. In the group with APPD between 30 and 40 mm, 7 children had an APPD that was smaller in the prone than in the supine position. Of the 15 children with APPD between 15 and 30 mm in the supine position 11 had a smaller
Table 1. No. Need for Pyeloplasty due to Renal Function Less Than 40% on Renogram
APPD Subsets in Supine Position
Total No./ Subset
No. No Change in APPD in Prone Position
Greater than 50 mm 40–50 mm 30–40 mm 15–30 mm Less than 15 mm
2 4 16 15 1
2 4 9 4 0
2 4 9 4 0
38
19
19
Totals
ANTEROPOSTERIOR DIAMETER OF RENAL PELVIS IN SUPINE AND PRONE POSITIONS
Table 2. APPD Subsets in Supine Position
Total No./ Subset
No. With Decrease Greater Than 10% of APPD in Prone Position
Greater than 50 mm 40–50 mm 30–40 mm 15–30 mm Less than 15 mm
2 4 16 15 1
0 0 7 11 1
38
19
Totals
None of the patients who had a decrease in APPD of greater than 10% in the prone position had deterioration of renal function on renogram and therefore, did not need pyeloplasty.
APPD in the prone position. These children had a greater than 10% decrease in APPD in the prone position. The only child in this study with an APPD smaller than 15 mm also showed a decrease in APPD in the prone position. The need for surgical intervention based on the differential function in the renogram of these children was studied. All children who had a decrease in APPD in the prone vs supine position had well preserved renal function. In addition, on serial followup ultrasounds they showed improvement with a progressive decrease in hydronephrosis. Of the 19 patients with no change in APPD in the supine and prone position there were 14 whose initial radionuclide study showed that the hydronephrotic kidney had a differential function of less than 40%. These cases were treated with pyeloplasty. There were 5 patients who showed no change in APPD in both positions. They had well preserved renal function during the initial renogram at 6 weeks (function of hydronephrotic kidney greater than 40%) and they were kept under observation. During the ultrasound examination done during followup there was an increase in the APPD with no change in the supine and prone positions, and worsening of hydronephrosis. Repeat renogram 3 to 6 months after the initial renogram in these 5 patients showed the hydronephrotic kidney had poorer function (less than 40%). Therefore, these 5 patients were treated with pyeloplasty.
DISCUSSION Prenatal detection of hydronephrosis has led us to a scenario in which the patient is presenting to the urologist before the baby is even born with a presumptive diagnosis rather than a symptom.13 In most cases the etiology of prenatal hydronephrosis is transient or physiological, has no clinical significance and is likely to resolve at the end of pregnancy or within the first year of life.14,15 In other cases prenatal hydronephrosis is associated with clinically important urological conditions. The dilemma then
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arises of how to differentiate clinically significant hydronephrosis from that which may resolve spontaneously. A common cause of newborn hydronephrosis is UPJ obstruction. Management of UPJ obstruction has triggered considerable debate, with some centers advocating early intervention while others recommend a more conservative approach.16 Ultrasonography and radionuclide renography are widely used to identify those patients who require pyeloplasty.9 The Great Ormond Street group has used anteroposterior pelvic diameter for assessment. They recommended simple followup for pelvic dilatations smaller than 12 mm and surgery for those larger than 50 mm. They also found that of those cases with an APPD larger than 40 mm, 80% needed surgery, while 55% of those with an APPD larger than 30 mm needed pyeloplasty.12,17 Onen reported that neither Society for Fetal Urology grading nor anteroposterior pelvic diameter could determine the severity of hydronephrosis, and he proposed an alternative grading system.7 Other investigators have used renal parenchymal area, calyx-to-parenchymal ratio and pelvis cortex ratio as a sonographic marker of UPJ obstruction.9 These various parameters have been evaluated to address the crucial decision in the management of unilateral UPJ obstruction of whether to intervene. Although the radionuclide renogram is a gold standard, the drainage curves from the initial renogram are not predictive of those requiring surgical intervention for UPJ obstruction.18 In our study the anteroposterior diameter of the renal pelvis was determined in the transverse plane in the supine and prone positions. This study started with a chance observation of one of the investigators (AS) that the APPD of one of the newborns was smaller in the prone than in the supine position. Subsequently all the children who presented to our center with a diagnosis of prenatally detected hydronephrosis were studied with APPD measured in the supine and prone position. In our study of 38 patients 30 were male and 27 had hydronephrosis on the left side. The preponderance of prenatal hydronephrosis in males and the dominance on the left side is well documented in the literature, although the side of kidney involvement does not determine the clinical outcome.19 There were 6 patients with an APPD larger than 40 mm and none showed any change in the prone position. The differential renal function on the renogram showed the hydronephrotic kidney had poorer function than the other normal kidney, and all these patients needed pyeloplasty. In the group of 16 children with an APPD between 30 and 40 mm in the supine position on the initial evaluation 7 had a difference of more than 10% in APPD measured in the supine and prone positions, with the diameter in the prone position
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ANTEROPOSTERIOR DIAMETER OF RENAL PELVIS IN SUPINE AND PRONE POSITIONS
smaller by at least 10% compared to the supine position (see figure). In addition, the initial renogram did not show much difference in the function of the renal units. On serial followup ultrasonography there was a decrease in the APPD in the prone and supine positions. The 9 patients in this group with no difference in the APPD in the prone and supine positions on initial ultrasound examination showed poor function of the hydronephrotic kidney on radionuclide renogram (6 immediate and 3 on followup), necessitating pyeloplasty. In the group with an APPD between 15 and 30 mm on initial evaluation 11 children had a smaller APPD in the prone than in the supine position. All showed normal function on renogram. Ultrasound evaluation during followup showed a decrease in the APPD in the supine and prone positions. By 1 year the APPD was 7 mm or smaller in these children. The 5 patients who showed no change in APPD in the supine and prone positions (3 in the 30 to 40 mm and 2 in the 15 to 30 mm group) had well preserved renal function on the renogram done at age 6 weeks. Ultrasound examinations on followup showed an increase in APPD with no change in the supine and prone positions. Repeat renogram demonstrated poor function of the hydronephrotic kidney, necessitating pyeloplasty. Thus, this study puts forth an interesting finding. If the initial postnatal ultrasound examination shows a decrease in the APPD in the prone vs supine position with the difference being greater than 10%, then these kidneys showed spontaneous resolution of or improvement in hydronephrosis and had well preserved renal function. Those patients with no change in APPD in the supine and prone positions had deterioration of renal function and needed surgical intervention (chi-square test p ⬍0.001).
The rationale for the smaller APPD in the prone position in cases which showed improvement and eventual resolution of hydronephrosis is easy to understand from the prone films taken during excretory urography. Prone positioning enhances the drainage of the renal pelvis and the collecting system empties rapidly in the ureters. Thus, the prone film of excretory urography is excellent for ureteral filling. In the prone position the lower pole of the kidney and the proximal end of the ureter are placed more anteriorly than the upper pole of the kidney. The pelvis also falls anterior to the psoas muscle. The pelvis and upper ureter fill more rapidly in prone position.20 –22 Thus, the nonobstructive dilated pelvis would drain better in the prone position and would have an APPD smaller than that in the supine position. Obstructed systems would not drain better in the prone position and, thus, the APPD in the supine and prone positions in these systems would be similar. A shortcoming of this study is the relatively small number of patients. However, the findings are important because the postnatal ultrasound can predict the possibility of resolution of prenatally detected hydronephrosis as well as identify that subset of patients for whom there is less chance of improvement of hydronephrosis. Identifying the latter subset of patients is imperative because waiting for a longer period by keeping them under observation can prove harmful to the renal parenchyma. Ransley et al have shown that kidneys with relative renal function as high as 40% can deteriorate during periods of observation.17 Following surgical relief of obstruction the relative renal function does not always return to the pre-deterioration levels. Postnatal sonographic measurement of APPD in the supine and prone positions can differentiate those newborns who will have improvement of hydronephrosis from those who are less likely to show such improvement. This can serve as a guide to determine the need for intervention before irreversible damage sets in.
CONCLUSIONS
Figure.
The dilemma in the management of prenatally detected hydronephrosis is to differentiate clinically significant hydronephrosis from that which may resolve spontaneously. Despite varying opinions regarding the management of prenatal hydronephrosis, the trend is toward a conservative approach.5 Of course, this should not be at the cost of increased risk of renal damage. In this study we propose simple bedside ultrasonography as a useful, noninvasive modality to identify kidneys at risk for damage and/or deterioration with time. Those cases with prenatally detected UPJ type of hydronephrosis and
ANTEROPOSTERIOR DIAMETER OF RENAL PELVIS IN SUPINE AND PRONE POSITIONS
an APPD smaller in the prone than in the supine position on postnatal evaluation show improvement in hydronephrosis on followup, whereas those cases in which there is no change in APPD in the supine and prone positions are at increased risk for damage. Thus, ultrasonography done in the prone and supine positions can help to differentiate nonob-
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structive dilatation from clinically significant obstructive dilatation. These findings in a small number of patients, if substantiated further by a larger multicenter study encompassing a larger patient pool, would definitely confirm that the first postnatal evaluation by ultrasonography is of immense predictive value in the treatment of these patients.
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