World J Urol (2004) 22: 73–78 DOI 10.1007/s00345-004-0405-0

T O P I C P A PE R

Marcus Riccabona

Assessment and management of newborn hydronephrosis

Received: 15 March 2004 / Accepted: 23 March 2004 / Published online: 12 June 2004 Ó Springer-Verlag 2004

Abstract The incidence of asymptomatic hydronephrosis in newborns is high. Despite extensive clinical and scientific research much controversy still exists about the assessment and management of hydronephrosis during infancy. Postnatal management demands a detailed prenatal history. Initial workup in newborns with unilateral hydronephrosis starts with a physical examination and sonography of the urinary tract on day 3–5. Grades 3 and 4 hydronephrosis are further investigated with a voiding cystourethrogram (VCUG) and diuretic renogram between weeks 4 and 6. An infant with an asymptomatic unilateral hydronephrosis of any grade, without urinary infection and stable washout, and stable normal differential function on serial controls can be managed conservatively. The goal of all therapeutic strategies in the management of newborn hydronephrosis is to select all infants with severe obstructive dilatation during serial follow-ups and to perform surgical repair before irreversible deterioration and functional renal damage occurs. Interdisciplinary cooperation between experienced pediatric urologists, nephrologist and radiologists is the basis for optimal decision making. Keywords Hydronephrosis Æ Management Æ Assessment Æ Newborn Æ Sonography

Is a newborn with dilated kidney a clinical enigma? The controversies involved in the assessment and management of newborns with hydronephrosis continue to

M. Riccabona Department of Pediatric Urology, Krankenhaus Barmherzige Schwestern, Seilersta¨tte 4, 4010 Linz, Austria E-mail: [email protected] Tel.: +43-732-76777470 Fax: +43-732-76777497

challenge pediatric urologists. The widespread use of pre- and postnatal ultrasonography since the late 1970s has led to the detection of a large population of newborns with asymptomatic hydronephrosis who require assessment. Most hydronephroses are detected at 18– 20 weeks of gestation, and the prevalence of fetal hydronephrosis, defined as a renal pelvic diameter >5 mm, is around 2%. Clinically significant hydronephrosis has an estimated incidence of 1 in 600 infants [2, 6]. Hydronephrosis does not necessarily imply obstruction, nor give any indication of function of the affected kidney [16]. Unfortunately, it is unclear how many of these dilatations represent true obstruction and, therefore, require treatment. Many cases of hydronephrosis will spontaneously improve or resolve with time postnatally, with no surgical intervention. There is still a lot of debate over the ability of different diagnostic tests to define obstruction or predict which kidney will benefit from surgical intervention. Therefore it is essential that postnatal management be reliable, efficient and economic [18].

Definitions Hydronephrosis is synonymous with dilatation of the pelvicalyceal system but not synonymous with obstruction. The degree of hydronephrosis is classified between grades I and IV according to the system of the Society of Fetal Urology (SFU) (Table 1), and the ultrasonographic appearance of the renal parenchyma and pelvicalyceal system on longitudinal ultrasonic section [9]. Additionally, the maximum anteroposterior diameter of the renal pelvis on the transverse ultrasonic section is an important and widely accepted parameter for defining and comparing hydronephrosis. Peters defined obstruction as ‘‘a restriction to urinary outflow that, if untreated, leads to renal deterioration’’ [12]. This is not clinically suitable in that a renal injury must be suffered in order to diagnose obstruction. The goal should be to diagnose obstruction prior to the damage being done.

74 Table 1 SFU grading system of congenital hydronephrosis Grade

Central renal complex

Renal parenchyma

0 1 2 3 4

Intact Slight splitting of the pelvis Evident splitting of pelvis and calices Wide splitting of pelvis and calices Further splitting of pelvis and calices

Normal Normal Normal Normal Reduced

Differential diagnosis Intermittent (transient) hydronephrosis and UPJ obstruction are by far the most common causes of postnatal hydronephrosis in the newborn, accounting for 70–80% of all dilatations of the collecting system. The next most common cause of congenital dilatation of the pyelocaliceal system is dilating reflux in approximately 15% of all cases. Other causes of hydronephrosis are listed in Table 2.

Postnatal assessment When an antenatal unilateral hydronephrosis is diagnosed, it is imperative to confirm the diagnosis postnatally. Postnatal management demands a detailed prenatal history, including gestational age at detection and a detailed description of the bladder, kidneys, amniotic fluid volume and any associated malformations. The initial assessment of a newborn with uni- or bilateral hydronephrosis includes a physical examination to detect a possible abdominal mass (hydronephrosis or multicystic kidney disease), or a palpable bladder. If the palpation is negative, further postnatal assessment should be started on day 3–5 (first week of life), ultrasonography earlier than this can lead to a false negative result, as neonatal urine production is reduced during the first 24–48 h. A number of infants have been seen who have gone from a virtually normal ultrasound to a rather marked hydronephrosis in a very short time. If no dilatation is detected, a repeat ultrasound should be performed within 4 weeks to avoid the chance that a significant obstructive uropathy may be masked by transient oliguria. If the postnatal ultrasound examinaTable 2 Causes of postnatal hydronephrosis Intermittent hydronephrosis Ureteropelvic junction obstruction Vesicorenal reflux Ureterovesical junction obstruction (megaureter) Ureterocele Ectopic ureter Dilatation of one moiety of a duplex kidney Posterior urethral valves Urethral atresia Prune belly syndrom Multicystic kidney desease

tion shows a unilateral hydronephrosis and a normal kidney on the opposite site, and the term newborn is asymptomatic, further investigations should be performed between weeks 6 and 8 when the kidneys have matured sufficiently. Severe bilateral hydronephrosis, severe hydronephrosis in a functional single system or a dilated posterior urethra suggestive of posterior urethral valves requires an immediate postnatal investigation including a blood test. In general, worrisome signs in the postnatal sonogram are caliectasis, a renal pelvic diameter >20 mm, a visualized dilated ureter or urethra, a ureterocele and abnormal renal echogenicity or cortical cysts.

Ultrasound Ultrasonography is the basic investigation in the assessment of newborn hydronephrosis. It offers fine visualisation of the renal parenchyma and the dilatation of the collecting system. Oral hydration is recommended before the start of a detailed examination, which should be performed with the bladder full as well as empty. The measurement of the maximum diameter of the renal pelvis in the transverse plane in combination with the SFU grading system greatly enhances the ability to evaluate the infant with hydronephrosis. Further information obtained includes caliceal dilatation, ipsilateral and contralateral renal length, cortical thickness and the echogenicity of the renal parenchyma. The evaluation of the full bladder in transverse and longitudinal sections, estimation of bladder wall thickness, the trigone and urine jet phenomenon, the bladder neck and the proximal urethra (partially using a transperineal approach) are mandatory. Additional assessment of the ureters, particularly at the uretero-pelvic and distal uretero-vesical junction, completes the sonographic evaluation of the urinary tract. In megaureter, the registration of peristalsis may be achieved using m-mode. Advanced ultrasound techniques such as extended field of view ultrasound, harmonic imaging, amplitude coded colour Doppler sonography, 3-D and 4-D ultrasound as well as the use of i.v. echo-enhancing agents have significantly improved the potential of ultrasound [14]. Koff and Campbell used compensatory changes in the opposite normal kidney as an obstruction parameter in unilateral hydronephrosis. Ransley and colleagues demonstrated that none of the children being followed for asymptomatic hydronephrosis with an A-P diameter in the transverse plane of the renal pelvis of <12 mm required surgical repair. Ultrasonography can also provide indirect evidence of infection when debris are seen as echogenic foci within the pelvicalyceal system. The use of diuretic ultrasound in the workup of hydronephrosis is based on the relative increase in the pelvicalyceal diameter after the injection of furosemide and the time taken for the renal collecting system to return to its initial dimensions. Although good results

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were recorded by some investigators, the lack of objective parameters to distinguish obstructive from nonobstructive hydronephrosis has limited the use of diuretic ultrasound [15].

Voiding cystourethrogram Several authors recommend a voiding cystourethrogram (VCUG) to rule out a vesicorenal reflux. It is tempting, especially in cases in which prenatal hydronephrosis has resolved, to avoid this invasive study. More recent studies have questioned the clinical significance of this reflux and several centers now advocate performing a VCUG only in patients with bilateral hydronephrosis, unilateral hydronephrosis with a dilated ureter or in any infant with suspected infravesical obstruction or variable dilatation of the upper tract suspicious of reflux. Absolute indications for VCUG are listed in Table 3. On the other hand, data have shown that approximately a 15– 25% of neonates with prenatal hydronephrosis will have reflux when checked [3, 19]. Indeed, even if the postnatal ultrasound is normal, a quarter of patients will have reflux. There remains the open question of whether the reflux is clinically relevant. However, patients with fetal reflux and sibling reflux are the only two types who may be diagnosed prior to urinary tract infection and in whom further renal injury may be prevented [20]. VCUG is carried out either using the transurethral or suprapubic techniques [11]. The suprapubic route is applicable even in the newborn. A eutectic mixture of local anaesthetic cream containing lidocaine and prilocaine is applied to the pubis 1 h before starting the procedure. Preliminary abdominal ultrasound is carried out to ensure adequate bladder filling, allowing safe bladder puncture. An 18–21 gauge needle is used to puncture the bladder. The needle is attached to a tube connected to a stopcock, enabling separate sterile urine aspiration and warmed contrast medium infusion, which is followed by intermittent fluoroscopic monitoring during filling and voiding. Fluoroscopic exposure is kept as brief as possible to lower the radiation dose, particularly to the ovaries. VCUG is still considered the gold standard for grading and classification (high or low pressure) of vesicouretral reflux (VUR) and a provides a reliable anatomical as well as functional assessment. In the follow-up, echo-enhanced cystosonography or direct or indirect radionuclide cystography can be used with a comparable sensitivity and specificity. Table 3 Absolute indications for VCUG Suspected infravesical obstruction Bilateral hydronephrosis Dilated ureter Duplex kidney Small kidneys Abnormal echogenicity Abnormal bladder Before pyeloplasty

Isotope studies Diuretic renography has become the method of choice for investigating dilatation of the upper urinary tract to evaluate renal function and drainage. The standard method (F+20 protocol) involves the administration of furosemide 20 min after the injection of the tracer. In this way, the effect of increased urine flow on the rising curve of the dilated pelvis or ureter and differential renal function can be detected. Four patterns of elimination have been identified during standard diuretic renography: normal (type I), obstructed (type II), dilated unobstructed (type IIIa) and equivocal (type IIIb) [10]. The current method of choice for neonatal renography is the 99m-technetium mercaptoacetyl-triglycine (MAG 3) scan, which has a high initial renal uptake, providing high kidney to background ratios with good resolution while the radiation burden to an obstructed kidney is less than with hippuran (0.20 – 0.38 mSv). The drainage curve is dependent on the state of hydration, the dose and timing of the administration of the diuretic and on renal function. It is also influenced by the size and distensibility of the renal pelvis and the bladder filling. In an attempt to improve the accuracy of diuretic renograms in the diagnosis of obstructive uropathy, various modifications of the technique and analysis have been introduced. In an attempt to quantify the washout rate in response to the diuretic, Kass et al. used half-time drainage (T1/2) as an objective tool in the diagnosis of obstruction [7]. T1/2 is defined as the interval necessary for half of the tracer to be eliminated after the administration of furosemide. Kidneys with a T1/2 of <10 min are considered unobstructed, those with <20 min obstructed, and those with 10–20 min as equivocal. Poor washout on a diuretic renogram may indicate an obstruction. It may also indicate poor renal function with insufficient diuresis, severe gross dilatation with insufficient diuresis or even a poorly made scan due to inadequate hydration or performed too soon after birth for good washout. The dynamic series of the diuretic renogram must be followed by a post micturition and late (120 min) image. English et al. assessed a modified method of diuretic renogram in which furosemide was administered 15 min before the injection of the tracer (F-15 protocol). The maximum effect of furosemide occurs 15 min after injection, and therefore results in maximum urinary flow rates at the start of the renogram. This helps to decrease the incidence of false positive results in grossly dilated or poorly functioning systems. The increase in urinary flow rate may be sufficient to cause obstruction in those systems that obstruct only at high flow rates, e.g. intermittent hydronephrosis. F-15 renography is recommended in either renographically or clinically equivocal cases [17]. Differential (‘‘split’’) renal function in the affected kidney reflecting tubular function is another important parameter in guiding the management of infants with hydronephrosis. Differential renal function measurements may be less

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accurate in the first few weeks of life than later. However, the goal is not absolute accuracy in the first scan, rather it is to determine good or poor function at the beginning and any change in function during follow-up and observation.

Magnetic resonance imaging For severe hydronephrosis with impaired renal function, and especially in patients with bilateral hydronephrosis, duplex systems or fusion anomalies, proper assessment of percent differential function and washout may be difficult even with the MAG 3 scan. In these cases, magnetic resonance urography (MRU) is useful and indicated, and has replaced traditional diagnostic methods which use ionising radiation (IVP). Nowadays, any fast T2-weighted sequence easily evaluates congenital hydronephroses and demonstrates the level of obstruction. Compared to IVP, MR-urography is more likely to display a very dilated and poorly functioning system. Using gadolinium enhanced T1-weighted sequences, it is possible to estimate the functional impairment and the remaining renal parenchyma [1]. Among problems to be solved in the future, the need for sedation or anaesthesia should be reduced due to the development of faster sequences.

Postnatal management To decide which infant can be managed non-operatively and which one requires surgical intervention is still a challenge. Despite extensive clinical and scientific research, much controversy still exists on various aspects of the postnatal management of newborn hydronephrosis.

Unilateral hydronephrosis SFU grades I and II An antenatally detected and postnatally confirmed hydronephrosis grade I or II should be investigated with VCUG. If this test is negative, antibiotic prophylaxis can be stopped and no isotope studies are necessary, but ultrasound control every 3 months during the first year of life is recommended. A positive VCUG (vesicorenal reflux grade III) justifies further antibiotic use and a dimercaptosuccinic acid scan should be made between weeks 4 and 6 in a term newborn. Even neonates whose antenatal hydronephroses resolves on the first postnatal ultrasound should undergo a VCUG, since several recent studies suggest that vesicorenal reflux may be the most common antenatal cause of hydronephrosis [5, 19]. The argument against the assessment of a hydronephrosis grade I or II is that it is often transient and does not justify the expense and potential risk of VCUG [3]. On the other hand, immediate diagnosis of reflux enables an early initiation of treatment before the development of

Table 4 Indications for surgery Reduced function (<40%) Sustained increase in hydronephrosis (dilatation, obstruction) Progressive deterioration (>5% SF) Febrile breakthrough infection, symptoms Unilateral gross hydronephrosis (>50 mm) Severe hydronephrosis in solitary kidney Severe (>30 mm) bilateral hydronephrosis

febrile urinary tract infection and the risk of renal deterioration.

Unilateral hydronephrosis SFU grades III and IV An antenatally detected and postnatally confirmed hydronephrosis grade III or IV needs further investigation. Diuretic renography should be performed between weeks 4 and 6. Additionally, VCUG is standard in most pediatric urology centers Table 3.

Bilateral hydronephrosis SFU grades III and IV Severe postnatally detected bilateral hydroureternephrosis necessitates an immediate VCUG (within 24–48 h) to rule out or confirm infravesical obstruction. Especially in the male infant, the possibility of outflow obstruction should always be considered first as the explanation for bilateral upper tract dilatation. A suprapubic catheter F 6 should be inserted, which can then be used for the VCUG.

Conservative management The natural history of hydronephrosis is nowadays better understood following several randomized studies comparing non-operative with surgical management of ante- or postnatally diagnosed disease. These studies have shown that the majority of patients with hydronephrosis improve spontaneously, however, approximately 25% require surgical intervention: the difficulty is to identify who needs an operation. This can be decided after a period of regular assessment. Diagnostic inaccuracies such as the variability of diuretic renograms and

Table 5 Parameters influencing operative vs conservative management Ipsilateral renal split function Symptoms (pyelonephrits) Breakthrough infection Serial washout in diuretic renogram Age Status of contralateral kidney Associated anomalies Compliance and preference of parents

77 Fig. 1 Diagnostic algorithm in unilateral hydronephrosis

the controversy in defining true urinary tract obstruction mandate observation as a first approach. Ransley and Koff and their co-workers pioneered the use of differential renal function, reserving surgical repair for those infants with a loss of more than 10% split function, and monitored contralateral, compensated kidney growth (‘‘aggressive observation’’) [18, 19]. Three conditions are required for the non-operative management of an infant with unilateral hydronephrosis: the child must be asymptomatic and free of febrile urinary infection, the hydronephrosis should be stable or decrease on repeated ultrasound scans, and the relative function on repeated diuresis renograms should be stable or increase. This

conservative approach, initially proposed by Ransely and Koff, is now followed by many centres and requires regular ultrasound examinations and diuretic renograms during the first year of life. These are the most common and important investigations in the follow-up of these patients. All infants with hydronephrosis grades III or IV should be maintained on antibiotic prophylaxis (trimethoprim 2 mg/kg or cephaclor 10 mg/kg for the night) for at least the first year of life, although this recommendation has not yet been confirmed by randomized prospective studies. The symptoms of urinary infection are not specific in this age group. Therefore any febrile illness necessitates a urinalysis.

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Operative management—indications for surgery In infants with severe hydronephrosis (SFU grades III or IV), impaired differential renal function (<40%), and obstructive washout in repeated diuretic renograms (at least two examinations within 2–3 months), surgical reconstruction is recommended. It is also indicated in severe hydronephrosis with primarily good function (SF 40–50%) during follow-up after febrile breakthrough urinary infection, in case of progressive hydronephrosis, and obstruction on ultrasound and diuretic renogram or clear deterioration of renal function (>5%) (Table 4) [4]. A good washout on nuclear scan questions the need of surgery. Coexisting contralateral kidney factors such as reflux, multicystic kidney disease, agenesis, aplasia or bilateral hydronephrosis, or ipsilateral factors such as VUR or ureterovesical junction obstruction may increase the indication for surgical repair (Table 5). Acute infection or a tense flank mass are contraindications for a pyeloplasty.

Conclusion The controversies involved in the assessment and management of newborn with asymptomatic hydronephrosis continue to challenge pediatric urologists. Ultrasonography, VCUG, serial diuretic renograms and MR urography in selected indications are the most important tools to assess congenital dilatation of the urinary tract (Fig. 1). Relevant criteria for the estimation of obstruction are repeated sonographic measurement of the renal pelvis in the transverse plane and serial evaluation of the washout and differential function in the diuretic renogram. The aim of any therapeutic management concept is to select the rather small group of infants with persistent or progressive ‘‘obstructive hydronephrosis’’, to operate them before irreversible renal deterioration occurs, and to spare all others unnecessary surgery.

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