The impact of fetal renal pelvic diameter on postnatal outcome

Prenat Diagn 2004; 24: 591–595.
Published online in Wiley InterScience ( DOI: 10.1002/pd.899
The impact of fetal renal pelvic diameter
on postnatal outcome
Ulrike John1*, Christiane K¨ahler2, Sven Schulz1, Hans Joachim Mentzel3, Susanna Vogt3 and
Joachim Misselwitz1
1Division of Pediatric Nephrology, University Children’s Hospital, Jena, Germany
2Department of Obstetrics and Gynaecology, Jena, Germany 3Institute of Diagnostic and Interventional Radiology Friedrich Schiller University, Jena, Germany Objectives To determine thresholds for the fetal renal pelvic anterior–posterior diameter (APD) predicting
postnatal clinically relevant pelvicaliceal dilatation.
Methods One hundred and forty-eight infants whose prenatal sonography had identified an isolated uni- or
bilateral fetal APD of ≥4 mm before 33 and/or ≥7 mm after 33 weeks’ gestational age were investigated postnatally. On the basis of postnatal ultrasound examination, these infants were grouped according to the Society for Fetal Urology Grading System: no pelvic dilatation (n = 38); only pelvic dilatation (n = 59); pelvicaliceal dilatation (n = 33); pelvicaliceal and ureter dilatation (n = 18).
Results Fetal pyelectasis of 7 mm was 89.3% sensitive and 78.9% specific <33 weeks, and ≥33 weeks
pyelectasis of 10 mm was 88.4% and 78.6% in predicting subsequent postnatal pelvicaliectasis, respectively.
Using a threshold of 4 mm <33 weeks and 7 mm ≥33 weeks yielded a sensitivity of 100% and a specificity of 18.7% and 47.8%, respectively. The median APD (range) at ≥33 weeks was 19 mm (9–36 mm) in patients requiring surgery and 13 mm (7–21 mm) in conservatively treated patients (p = 0.001). Thirteen of fourteen patients with APD ≥19 mm underwent surgery.
Conclusion Women with ultrasonographically detected prenatal fetal pelvic dilatation of ≥4 mm before
33 weeks and of ≥7 mm from 33 weeks onwards of gestation should have repeated prenatal ultrasound scans and a detailed postnatal evaluation. The dilatations of an APD >4 mm before 33 weeks, which have disappeared at the post-33-week scan need no further investigation in the postnatal period. Copyright  2004 KEY WORDS: fetal; renal; pyelectasis; ultrasonography; prenatal diagnosis investigation (Anderson et al., 1995; Corteville et al., 1991; Fasolato et al., 1998; Mouriquand et al., 1999; Fetal pyelectasis is the most common prenatal diag- Kent et al., 2000, Siemens et al., 1998). The outcome nosed malformation with 0.2 to 1% of all pregnancies and proper management of fetal hydronephrosis are not (Thomas, 1990). Fetal renal pelvic dilatation is com- defined sufficiently. The prognosis of obstructive uri- monly observed during prenatal ultrasound examina- nary tract anomalies is variable and depends on several tions, but its clinical significance remains unclear. The conditions: the gestational age at diagnosis, the local- number of otherwise healthy fetuses that are diagnosed ization of the stenosis, the bilateral or unilateral alter- with this condition is on the increase, with the growing ation of the kidneys, and the amount of amniotic fluid use of ultrasound in obstetrics. As a result, more infants as an indicator for renal function. Spontaneous reso- with this history are being presented to pediatricians, lution has been described as well as the progression nephrologists and urologists. The most common uri- into a severe obstruction with development of cystic nary tract abnormality is a nonspecific hydronephrosis.
renal dysplasia and the loss of renal function (Sohn Almost half of all prenatally diagnosed hydronephroses and Tercanli, 2003). In general terms, the pediatrician’s that are found after investigation are an isolated upper- goal concerning newborns diagnosed with pyelectasis tract dilatation. This population has posed the greatest or hydronephrosis should be to strike the right balance challenge in prospectively determining which of these between excessive medical intervention (long, costly and asymptomatic children have an obstruction that would often useless follow-ups, which arouse unjustified and/or benefit from surgery, as opposed to a simple dilatation disproportional parental anxiety) and sufficient interven- that may be inconsequential to their well-being (Dhillon, tion to diagnose potentially dangerous conditions (Fanos 1998). Various cut-off values for dilatation of the fetal renal pelvis are being described as requiring postnatal This study was performed in order to assess the clini- cal impact of prenatal ultrasonographically detected fetal renal pelvic dilatation and to determine thresholds for the *Correspondence to: Ulrike John, Division of Pediatric Nephrol- ogy, University Children’s Hospital, Kochstrasse 2, 07740 Jena, fetal renal anterior–posterior diameter (APD) predicting Germany. E-mail: [email protected] postnatal clinically relevant pelvicaliceal dilatations.
Copyright  2004 John Wiley & Sons, Ltd.
was performed to evaluate function and drainage. An obstructive washout pattern was defined as the half-time One hundred and ninety-six pregnant women were radiotracer washout longer than 20 min (O‘Reilly et al., referred to our university hospital (from January 1990 to December 1999) because of a suspected renal anomaly, An indication for surgery was given: (1) if the identified during a prior external ultrasonographic exam- hydronephrotic kidney showed decreased differential ination. They were to be examined using the espe- function (<40%) and an obstructive type of the washout cially fine diagnostics permitted by ultrasonography uti- curve in diuresis renography; (2) in cases with normal lizing a 3.75 MHz transducer (Toshiba SSA 270 A).
differential function but an obstructive type of drainage All 196 infants had postnatal nephro-urological exam- curve at least in two investigations in combination with ination. One hundred and forty-eight patients were an unchanged or increased pelvicaliceal dilatation.
included in this study with: (1) prenatal isolated uni- or bilateral renal pelvic dilatation defined as fol- Statistical analysis
<33 weeks of gestation anterior–posterior diam- eter (APD) ≥4 mm and ≥33 weeks of gestation APD ≥7 mm; (2) postnatal ultrasound diagnosis for each kid- Multiple thresholds were analyzed for the fetal renal ney according to the Society for Fetal Urology grad- pelvic APD and correlated with infant outcome. The goal ing system (Fernbach et al., 1993) at the age of three was to choose the threshold with the highest sensitiv- months: (a) normal (NORMAL): without any pelvic ity for predicting congenital pelvicaliceal dilatation. The dilatation, (b) pyelectasis (PYECT): without caliceal receiver-operating characteristic (ROC) plots of various dilatation or when a few but not all calices are identified, fetal APD thresholds were created from sensitivity ver- (c) pelvicaliceal dilatation (PCD), (d) dilated ureter and sus 1-specificity calculated from cross-tables to discrim- inate between kidneys with and without a subsequent In our management, micturating cystourethrography postnatal relevant pelvicaliceal dilatation (kidneys with (MCUG) is not recommended for all infants with PCD or UPCD). The Kruskall–Wallis test was used to prenatal pelvic dilatation. We performed MCUG only in confirm differences between the various groups of diag- those 55 of 152 infants with postnatal PCD or UPCD.
nosis followed by comparison in pairs (Mann Whitney We found bilateral refluxes in four infants (two boys, U-test). Differences were considered to be statistically two girls; grade 3 in three kidneys, grade 4 in four and significant at a P-value <0.05.
grade 5 in one kidney). Since this diagnosis may only be made by virtue of the postnatal MCUG, which was not performed in all patients of our study, these four cases Forty-four of one hundred and ninety-six patients with gross structural anomalies of the urinary tract were excluded prior to entry of study analysis: duplication From 148 infants, a fetal pelvic dilatation was diag- (n = 11), multicystic dysplastic kidney (n = 16), poste- nosed, which was bilateral in 72 and unilateral in 76 rior urethral valves (n = 3), and miscellaneous (n = 14).
fetuses. Postnatally, we found bilateral NORMAL kid- A total of 433 prenatal and 502 postnatal ultrasound neys in 38 infants. Sixty-eight infants had unilateral investigations in 148 patients were performed at an involvement with the diagnoses PYECT, PCD, UPCD, average of 6.3 scans per patient. All 148 patients with and 42 bilateral combined with corresponding diagnoses.
296 renal units had at least one ultrasound examination Finally, for further analysis of renal APD, we consid- before and/or after 33 weeks of gestation. Measurement ered all 296 kidneys (148 patients) including postnatal of the APD only before 33 weeks of gestation was diagnoses: NORMAL: n = 144; PYECT: n = 98; PCD: performed in 35, only after 33 weeks of gestation in n = 33 and UPCD: n = 21.
51, and in both time periods in 62 patients. In our retrospective study, we did not evaluate the reasons for APD in prenatal ultrasound scans
no further renal scan in pregnancy for the 35 subjects who had only one renal scan. Finally, 194 kidneys were examined before 33 weeks’ gestation and 226 kidneys The median (range) APDs of the prenatal scans below ≥33 weeks’ gestation, respectively. Prenatal ultrasound 33 weeks of gestational age found in the various groups was done at a median (min; max) fetal patient age of 23 weeks of gestation (min 18; max 32) in the group (1.0–9.0), 6.6 mm (3.5–16.0), 10.8 mm (6.0–28.8) and <33 weeks of gestation and 37 weeks (min 33; max 41) 7.1 mm (4.0–13.0), respectively. The corresponding val- in the group of over 33 weeks of gestation. After birth, ues of APDs ≥33 weeks of gestational age were 5.0 mm all 148 infants were followed-up, performing at least one (2.0–15.0), 9.0 mm (2.3–18.0), 18.0 mm (7.1–36.0) ultrasound examination until three months of life using and 13.8 mm (8.0–32.0), respectively.
a 5 to 7 MHz transducer (Acuson 128 XP-10). Median At 18 to 32 weeks’ gestation, significant differences follow-up time was 1.14 years (min 0.01; max 9.1) in of the fetal renal pelvic APD of NORMAL kidneys versus PYECT, PCD and UPCD were found by com- In all infants with PCD or UPCD, at least one 99m- parison in pairs (p < 0.001), although the APDs of kid- TcMAG 3 diuresis renography with furosemide washout neys with UPCD compared with PCD or PYECT did Copyright  2004 John Wiley & Sons, Ltd.
Prenat Diagn 2004; 24: 591–595.
THE IMPACT OF FETAL RENAL PELVIC DIAMETER Figure 1—Median renal APDs (mm) of the prenatal scan ≥33 weeks’ gestation (n = 226 kidneys) found in the various groups with postnatal Figure 2—(a) Receiver operator characteristic curves illustrating the not show significant differences (p = 0.054, p = 0.240, ability of the fetal renal pelvic APD (mm) <33 weeks’ gestation to distinguish between kidneys with (n = 28) and without (n = 166) At the time period 33 to 41 weeks’ gestation, the fetal a subsequent postnatal relevant pelvicaliceal dilatation. (b) Receiver renal pelvic APDs differed significantly for the various operator characteristic curves illustrating the ability of the fetal kidney diagnoses: NORMAL, PYECT, PCD and UPCD renal pelvic APD (mm) ≥33 weeks’ gestation to distinguish between kidneys with (n = 43) and without (n = 182) a subsequent postnatal (p < 0.0001). However, no significant difference of the renal APD between PCD and UPCD (p = 0.242) was found (Figure 1). Of 62 infants who did have more than of thirty-three kidneys with PCD and 8 of 21 kidneys one scan before and after 33 weeks, eight had an APD with UPCD required unilateral surgical treatment. Alto- below 7 mm in both kidneys at the post-33-week scan.
gether, 25 of 148 children (17%) had surgical treatment.
Moreover, they had no renal dilatation in the scan after In order to test the differences of the renal pelvic APD at various gestational periods between surgically and ROC analysis predicting subsequent
conservatively treated children, only the children with postnatal diagnosed pelvicaliceal dilatation (PCD and postnatal pelvicaliceal dilatation
At <33 weeks’ gestation, the median APDs (range) Using a threshold of 7 mm, it was found that fetal <33 weeks’ gestation of conservatively treated patients renal pelvic dilatation was 89.3% sensitive and 78.9% (n = 17) and surgically treated patients (n = 17) were specific at <33 weeks (Figure 2a). The best correspon- 10.3 mm (4–19) and 11.0 mm (7–23), respectively dence between sensitivity and specificity ≥33 weeks showed the threshold of 10-mm renal pelvic dilatation At 33 to 41 weeks’ gestation, the median APDs with 88.4% and 78.6% in predicting subsequent pelvi- (range) in conservatively treated (n = 16) and in patients caliceal dilatation, respectively (Figure 2b). This was requiring surgery (n = 23) were 13.3 mm (7–21) and accomplished by using a receiver-operating characteris- 19.0 mm (9–36), respectively (p = 0.001) (Figure 3).
tic curve categorizing the prenatal sonograms into gesta- Thirteen of fourteen patients who had an APD tional periods and varying the threshold of APD in each ≥19 mm at the 33 to 40 weeks’ gestational period period. Using a threshold of 4 mm (<33 weeks) and underwent surgical intervention postnatally.
7 mm (≥33 weeks) yielded a sensitivity of 100% and a specificity of 18.7 and 47.8%, respectively (Figure 2a,b).
APD in surgically and conservatively
treated patients
Prenatal ultrasonography has identified a large popu- lation of fetuses with a urinary tract abnormality that All infants with only uni- or bilateral NORMAL and is most commonly a nonspecific upper-tract dilatation PYECT (n = 97) were treated conservatively. Seventeen with or without ureteric dilatation. Ultrasonographic Copyright  2004 John Wiley & Sons, Ltd.
Prenat Diagn 2004; 24: 591–595.
10 mm ≥33 weeks’ gestation yielded the highest com- bined sensitivity and specificity (89 and 78%, respec- tively) for predicting a subsequent pyelocaliectasis. In order to identify all ‘at risk’ fetuses, a lower fetal renal APD of ≥4 mm before 33 weeks and ≥7 mm ≥33 weeks would be required. The specificity, however, asso- ciated with these thresholds would be 18.7 and 47.8%, respectively. An APD of ≥4 mm at the first trimester is the most commonly used cut-off to denote hydronephro- sis (Stocks et al., 1996; Sairam et al., 2001; Adra et al., 1995; Kitagawa et al., 1998). A recent study revealed that the third trimester anterior–posterior renal pelvis diameter of ≥7 mm was the best ultrasound criterion to predict postnatal uropathies (Ismaili et al., 2003).
Ouzounian et al. (1996) have demonstrated that fetal pyelectasis of 8 mm produced the best combination of sensitivity and specificity, 91 and 72% respectively.
In order to achieve 100% sensitivity, they recommend postnatal renal ultrasonography for patients with fetal pyelectasis of ≥5 mm at any gestational age. Mandell et al. (1991) found that the degree of dilatation did not correlate well with postnatal findings. They there- fore recommended clinically significant thresholds for pyelectasis of 5 mm between 15 and 20 weeks, 8 mm between 20 and 30 weeks and >10 mm after 30 weeks.
By using a cut-off value of 10 mm as recommended by other authors (Sairam et al., 2001), 11% of the neonates Figure 3—Median fetal renal pelvic APD (mm) in patients <33 and of our study would not have been recognized. The false- ≥33 weeks’ gestation with surgery versus conservative therapy in positive rate declines with advancing gestational age. A critical note to these high demands for security is the fact that they may lead to unwarranted parental concern identification in utero of fetuses at risk of subsequent as well as expensive postnatal diagnostic studies. In 8 pelvicaliceal dilatation can minimize diagnostic delays of 62 infants (13%), the fetal renal APD had resolved and potentially reduce morbidity (Ouzounian et al., <7 mm at the post-33-week scan and showed no dilata- 1996). Our approach was to predict such fetuses that will tion postnatally. Our findings support the results of Kent suffer from significant renal pathology to be identified et al. (2000) that the fetus with a normal repeat ultra- sound at 28 to 34 weeks would not require a postnatal The fetal renal APD was analyzed before and after 33 weeks of gestation. The APD of the fetuses with For our application, the important practical criterion subsequent neonatal PCD was different from those with in prenatal ultrasonography to distinguish future abnor- no dilatation or pyelectasia at any gestational period.
mal postnatal ultrasound scans for the diagnostics of Whereas the fetal renal APD of fetuses with future PCD and UPCD include pelvic, caliceal and/or ureteral neonatal PYECT and UPCD did not differ in the early dilatation and changing dilatation during the examina- period below 33 weeks of gestational age, the distinction tion. Measurement of the fetal renal APD has emerged as after this time was significant (Figure 1). The fetal renal a sensitive and accurate technique for the 100% identifi- APD showed no difference between PCD and UPCD cation of children with possible fetal renal abnormalities.
at any prenatal period. Therefore, the crucial role of Surgical rates from 7 to 40% in children with pre- the ureter distinguishing PCD from UPCD will be clear natal hydronephrosis have been described (Gunn et al.
in the portrayal using ultrasound scan as mentioned by 1995; Corteville et al., 1991). The largest prospective other authors (Stocks et al., 1996; Wilson et al., 1997; study of Sairam et al. (2001) in an unselected routine Langer et al., 1996; Anderson et al., 1997; McIlroy obstetric population of 11 465 children revealed 11 of et al., 2000; McLellan et al., 2002).
75 fetuses (15%) with hydronephrosis who underwent The measurement of the anterior–posterior renal postnatal surgery. In our study, 25 of 148 children (17%) pelvic diameter by ultrasonography has proved to be underwent postnatal surgery. All of them had PCD or the most useful tool for identifying the group that needs UPCD. None of the children with simple pelvic dilata- close follow-up from those patients who need minimal tion required surgery. The fetal renal APD of postna- imaging (Dhillon, 1998). There is, however, no agreed tally surgically treated patients compared with conserva- definition of ‘significant’ prenatal renal pelvic dilatation, tively followed-up patients showed no difference below which warrants further postnatal investigations (Morin 33 weeks’ gestation. After this time, however, the dif- et al., 1996; Anderson et al., 1995; Ismaili et al., 2003).
ference was highly significant. Our study shows that Results of our study indicate that a fetal pyelectasis fetuses with APD ≥19 mm after 33 weeks’ gestation threshold of 7 mm before 33 weeks’ gestation and of have a significant risk of postnatal surgery. The study Copyright  2004 John Wiley & Sons, Ltd.
Prenat Diagn 2004; 24: 591–595.
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Fernbach SK, Maizels M, Conway JJ. 1993. Ultrasound grading of surgery at infancy (11 ± 6 mm) was significantly less hydronephrosis: introduction to the system used by the Society for than those requiring surgery (30 ± 14 mm, p < 0.01). In fetal urology. Pediatr Radiol 23: 478–480.
accordance with our results, Gotoh et al. (1998) recom- Gotoh H, Masuzaki H, Fukuda H, Yoshimura S, Ishimaru T. 1998.
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Kent A, Cox D, Downey P, James SL. 2000. A study of mild fetal pyelectasia—outcome and proposed strategy of management.
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Copyright  2004 John Wiley & Sons, Ltd.
Prenat Diagn 2004; 24: 591–595.


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