Page 2 - Canadian Urological Association/Pediatric Urologists of Canada guideline on the investigation and management of antenatally detected hydronephrosis

Capolicchio et al

America has been the classification from the Society for 6 mm at 18 years, with the 99th percentile for children <5
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Fetal Urology (SFU) (Table 1). The SFU grading classifica- years of age being <10 mm. 1
tion has been validated with good intra-rater reliability and Aside from APD, the severity of hydroureteronephrosis
modest inter-rater reliability, with Grade 3 being the least (HUN) has also been classified by the SFU based on the
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reliable. The SFU has recently proposed the UTD classi- transverse measure of the distal ureter; Grade 1 is <7 mm,
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fication, which combines elements of both APD and SFU. Grade 2 is 7‒10 mm, and Grade 3 is >10 mm. This clas-
Initial validation has been possibly more reliable than the sification is mostly descriptive and has not been submitted
SFU system, 10,11 with others showing the same issues with to much scrutiny. The dilated fetal bladder or megacystis has
inter-rater reliability. The UTD classification for HN was been defined based on the formula for fetal bladder sagittal
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released to address potential shortcomings of the current length (FBSL) in mm = gestational age in weeks + 2. 15
SFU grading system; more specifically, to deal with incon- It is important to remember that a dilated urinary tract
sistencies between prenatally detected HN and postnatal does not automatically infer obstruction of the urinary tract.
management strategies within and across specialties. The Whereas hydronephrosis equates a dilated renal collecting
UTD classification uses a three-point system based on six system, obstruction cannot be proven on the basis of any
different US observations (renal pelvis APD, calyceal dila- single imaging study, hence the need for a period of obser-
tion, parenchymal thickness/appearance, ureteral dilation, vation to demonstrate deterioration over time.
and bladder abnormalities) to stratify patients into three risk
categories based on the most concerning of six US variables Antenatal vs. postnatal followup
(UTD P1, P2, and P3): UTD P1 (low-risk) with 10‒15 mm
renal pelvis APD and central calyceal dilation to UTD P3 The frequency of antepartum followup of a pregnant mother
with renal pelvis APD >15 mm, peripheral calyceal dilation, is left to the discretion of the obstetrician. While AHN is
parenchymal thinning, ureter dilation, and or bladder abnor- more common in fetuses with serious chromosomal anom-
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mality (high-risk). Nevertheless, the added complexity of alies, most sources do not recommend routine karyotyp-
the UTD classification imposes a need for greater validation ing for all cases of isolated AHN. However, this may be
prior to supplanting the simplicity of the SFU classification. considered in the presence of multiple system anomalies. 1
Second trimester AHN is often followed up so that progres-
Definition of the dilated urinary tract sion of severity can be detected and appropriate postnatal
followup planned. Cases with severe bilateral AHN and/or
The diagnosis and management of the fetus or child with a oligohydramnios raise concern over potential renal failure
dilated urinary tract requires an understanding of what are and are often referred to the pediatric urologist for antenatal
acceptable degrees of dilation (Table 2). 1,14 The definitions of counselling. Other concerning sonographic findings include
pyelectasis, hydroureter, and megacystis will determine the renal cortical hyper-echogenicity, renal cortical cysts, and a
intensity of investigations and frequency of followup, both dilated bladder. The evaluation and selection of cases for in
antenatally and postnatally. It is generally accepted that pye- utero intervention is beyond the scope of this guideline, but
lectasis in the third trimester is defined as APD >4‒5 mm. 1 treating physicians should be aware that many tertiary care
Nevertheless, the ideal cutoff for routine postnatal screening centres offer interventions, such as vesico-amniotic shunting,
remains controversial, since high grades of AHN can resolve in selected cases of bladder outlet obstruction in the setting
postnatally and conversely low grades can deteriorate; not- of multidisciplinary teams. The impact of prenatal diagnosis
withstanding, most centres use a cutoff of 7 mm in the third of HN is also a subject of lengthy discussion; one is referred
trimester for indicating a postnatal evaluation. Postnatal data to the excellent reviews by Thomas. 3,4
on magnetic resonance imaging (MRI), not US, suggest that Postnatal resolution has been noted in 25‒50% of AHN
the normal APD in children is 3 mm at one year of age, cases. 1,16 Of those persisting postnatally, the majority will be
low-grade (Table 3). In view of this, most centres will refer
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cases for postnatal evaluation if the third trimester APD is
Table 1. SFU grading of hydronephrosis >7 mm, despite the fact that >4 mm is considered abnormal
SFU grade Ultrasound findings
0 Normal kidney (resolved antenatal hydronephrosis)
Table 2. Severity of antenatal hydronephrosis (AHN) by
1 Pyelectasis
APD 14
2 Pyelectasis with dilation of 1 or more major calyces Degree of ANH Second trimester Third trimester
(caliectasis)
3 Pyelectasis with dilation of all 3 major calyces Mild 4 to <7 mm 7 to <9 mm
4 Pyelectasis with parenchymal thinning compared to Moderate 7 to ≤10 mm 9 to ≤15 mm
contralateral kidney Severe >10 mm >15 mm
SFU: Society for Fetal Urology. APD: antero-posterior renal pelvic diameter.

86 CUAJ • April 2018 • Volume 12, Issue 4