Prenatal caliectasis/hydronephrosis

OVERVIEW: What every practitioner needs to know

Are you sure your patient has antenatal hydronephrosis? What are the typical findings for this disease?

Antenatal hydronephrosis is not a disease, it is a sonographic finding that may be associated with a congenital malformation of the urinary tract or not. It is usually diagnosed on the obstetric morphological ultrasound (2nd trimester). Findings include dilatation of the renal pelvis and/or calyces and, less commonly, the ureter. Most cases are unilateral.

Most patients with antenatal hydronephrosis will not have significant postnatal urological pathology requiring surgery.

Patients seen postnatally for antenatal hydronephrosis are usually asymptomatic. Clinically, the main symptom to watch for in babies that had hydronephrosis prenatally is urinary tract infections (UTI). In infants it should be suspected in the setting of isolated unexplained fever and ideally confirmed with a catheter urine specimen obtained using sterile technique.

Definition of antenatal hydronephrosis:

Hydronephrosis = fluid in the kidney and, as such, it is a descriptive term, not necessarily indicative of a pathological condition.

Quantitative – Ultrasound measurement of the AP diameter of the pelvis ≥4mm before 30 weeks and ≥7mm after 30 weeks of gestation.

Qualitative – Society for Fetal Urology (SFU)

Grade I – splitting or separation of the renal pelvis

Grade II – moderate dilatation of the renal pelvis with no calyceal dilatation

Grade III – pelvic and calyceal dilatation with normal thickness of the renal parenchyma

Grade IV – pelvic and calyceal dilatation associated with parenchymal thinning

What other disease/condition shares some of these symptoms?

Differential diagnoses potentially associated with antenatal hydronephrosis and their incidences (based on SFU consensus 2010):

Nonspecific hydronephrosis that will undergo spontaneous resolution – 41-88%

Ureteropelvic junction obstruction (UPJO) – 10-30%

Vesicoureteric reflux (VUR) – 10-20%

Megaureter – 5-10%

Multicystic dysplastic kidney (MCDK) – 4-6%

Posterior urethral valves (PUV) / Urethral atresia – 1-2%

Ureterocele / Ectopic ureter associated with a duplex collecting system – 5-7%

Prune-belly syndrome (PBS), VACTERL association, Cloacal anomaly, Mullerian anomalies – rare

What caused this disease to develop at this time?

In most patients, antenatal hydronephrosis represents a transient dilatation of the collecting system that is not associated with any pathology and will resolve over time. Underlying pathology, whenever present, is represented by congenital anomalies of the urinary tract for which causal factors have not been elucidated.

Antenatal hydronephrosis is more likely to be linked to postnatal pathology when it is bilateral, associated with oligohydramnios, parenchymal thinning, calyceal dilatation, ureteral dilatation, chromosomal anomalies or multiple system malformations.

What laboratory studies should you request to help confirm the diagnosis? How should you interpret the results?

Patients with bilateral hydronephrosis, especially if associated with bilateral hydroureters and a distended bladder, should have blood sent for renal function tests and serum chemistries, bearing in mind that in the first week of life, the measured creatinine is usually maternal. An initial abnormally high creatinine is associated with a poor renal prognosis.

Patients with unilateral hydronephrosis and a normal contralateral kidney DO NOT need any bloodwork whatsoever.

Physical examination

  • Initial physical examination of the newborn with antenatal hydronephrosis should include:


    assessment of respiratory function – severe malformations such as PUV can be associated with oligohydramnios and pulmonary hypoplasia.

    potential associated anomalies, particularly the VACTERL association (Vertebral, Anorectal, Cardiac, TE- esophageal atresia / tracheoesophageal fistula, Renal, Limb anomalies).


    abdominal inspection and palpation – inspection can reveal skin folds, like seen with PBS; large hydronephrotic kidneys can be palpable; in fact, a palpable abdominal mass in the newborn should be considered renal until proven otherwise (usually hydronephrosis or MCDK).

    examination of the external genitalia

    male – inspection of the penis, position of the urethra, palpation of testicles, patency of the anus.

    female – inspection for separate openings for urethra and vagina, prolapsed ureterocele, patency of the anus.

    back examination – inspection looking for stigmas associated with spina bifida oculta, such as hair tufts, sacral dimples, hemangiomas, asymmetries, which could be associated with a neurogenic bladder.

One should keep in mind that in boys with bilateral hydronephrosis, especially in the setting of bilateral hydroureters and a thickened bladder, a diagnosis of posterior urethral valves (PUV) MUST be contemplated and action taken accordingly (see below).

Would imaging studies be helpful? If so, which ones?

Ultrasound – every patient with antenatal hydronephrosis should get a postnatal ultrasound of the urinary tract. In situations where a severe abnormality is suspected, i.e. bilateral hydronephrosis with bilateral hydroureteres in a boy raising the suspicion for PUV, the ultrasound should be performed immediately in the neonatal period. In patients with unilateral hydronephrosis, the initial ultrasound can be safely postponed until 4-6 weeks of life. Whenever a decision is made to perform an ultrasound in the neonatal period, it should be done after the first 48hs of life, because of physiologic dehydration. Patients with a normal neonatal ultrasound should have a repeat study after 3-6 months of life.

Voiding Cystourethrogram (VCUG) – clearly indicated if PUV is suspected. Consensus from SFU recommends a VCUG in the setting of a dilated ureter, however, we feel that this approach does not have a clear impact on management and the test should be based on informed consent by the family. It is highly debatable whether a VCUG should be performed for patients with high-grade isolated unilateral hydronephrosis to diagnose vesicoureteric reflux, but our impression is that it is NOT indicated, since there doesn’t seem to be an appreciable difference in the incidence of VUR between patients with antenatal hydronephrosis and the general population.

Nuclear scan – two types of nuclear scans (Lasix and DMSA) may be indicated to complete the evaluation for antenatal hydronephrosis. Due to renal immaturity, a nuclear scan should not be performed until 6 weeks of age.

Lasix scan (preferred tracer – MAG 3) – used for situations where an obstruction is suspected. In patients with high-grade hydronephrosis and no ureteric dilatation, it might aid in the diagnosis of UPJO and provide insight into the differential renal function.

DMSA scan – best study to look for signs of dysplasia, scars post-infection and split function between the two kidneys.

Magnetic resonance urography (MRU) – recent addition to the diagnostic armamentarium for antenatal hydronephrosis. Holds promise due to the possibility of both anatomical and functional assessment simultaneously. Still not widely available and more studies with clinical correlation are required.

Confirming the diagnosis

See Figure 1 for the algorithm for the management of antenatal hydronephrosis (detailed explanation for each recommendation can be found under the imaging studies and initial management headers).

Figure 1.

Algorithm for the initial evaluation of antenatally-diagnosed hydronephrosis. Levels of evidence for each intervention are depicted in the boxes. SFU – Society for Fetal Urology hydronephrosis grading system (from 0-4).

* some authors recommend the use of prophylactic antibiotics, especially in higher grades of hydronephrosis (grade D).

If you are able to confirm that the patient has antenatal hydronephrosis, what treatment should be initiated?

Fetuses with unilateral hydronephrosis DO NOT require any prenatal intervention whatsoever.

Male fetuses with bilateral hydroureteronephrosis, thick-walled bladder and new-onset oligohydramnios may be considered for prenatal intervention in the form of vesico-amniotic shunting, provided they have a normal karyotype and no other major anomalies. The primary goal of the procedure is to avoid pulmonary hypoplasia, which can be lethal, but not progression to end-stage renal disease.

Fetuses that do not fit into the aforementioned criteria should be dealt with postnatally.

It is highly debatable whether patients with severe hydronephrosis (grades III and IV) should be placed on prophylactic antibiotics and/or have a circumcision if males. Despite some studies suggesting there is an increased risk for UTI in this population, no good quality trials have been published to support this approach.

If a decision is made to start antibiotics, cephalexin or amoxicillin are usually the drugs of choice in the neonatal period.

In our experience, trimethoprim (witohut the sulfa component) has a safe profile in that period too.

Referral to pediatric urologist if persistent hydronephrosis postnatally.

Postnatal workup based on the “imaging studies” section description.

Decision about need for surgical management will be largely dependent on symptoms coupled with imaging studies. In summary, clinical indications for surgical intervention will be recurrent UTI, episodes of flank pain (older children) and worsening hydronephrosis on ultrasound associated with decreased renal function on renal scan (< 40%).

What are the possible outcomes of antenatal hydronephrosis?

  • Most patients with antenatal hydronephrosis will undergo spontaneous resolution without any long-term consequences or the need for any intervention.

  • Final possible outcomes are diverse depending on coexisting pathology.

  • The likelihood of requiring surgical intervention is low and dependent on underlying pathology.

  • Patients with higher grades of hydronephrosis are more likely to require surgical treatment.

What causes this disease and how frequent is it?

Antenatal hydronephrosis is present in 1-5 % of all pregnancies and is the most common anomaly detected by prenatal ultrasounds.

What complications might you expect from the disease or treatment of the disease?

  • Main complications associated with antenatal hydronephrosis are:


    decreased renal function

    risk of renal failure (only in bilateral cases)


What is the evidence?

Evidence is largely based on retrospective series. There are no prospective studies or RCTs addressing the issues discussed in this chapter.


Nguyen, HT, Herndon, CDA, Cooper, C. “The Society for Fetal Urology consensus statement on the evaluation and management of antenatal hydronephrosis”. J Pediatr Urol. vol. 6. 2010. pp. 212-231. (Broad review of the published literature on the subject with a consensus statement by a panel of experts.)

Lee, RS. “Antenatal Hydronephrosis as a Predictor of Postnatal Outcome: A Meta-analysis”. PEDIATRICS. vol. 118. 2006. pp. 586-593. (One of the few meta-analysis that correlates degree of prenatal hydronephrosis with postnatal outcomes.)

Mallik, M, Watson, AR. “Antenatally detected urinary tract abnormalities: more detection but less action”. Pediatr Nephrol. vol. 23. 2008. pp. 897-904. (Results from a cohort study comparing two different time periods in a large referral center that follows a strict protocol for diagnosis and management of antenatal hydronephrosis.)

Thomas, DFM. “Prenatal diagnosis: what do we know of long-term outcomes?”. J Pediatr Urol. vol. 6. 2010. pp. 204-211. (One of the few papers that addresses long-term outcomes of patients with antenatal hydronephrosis.)

Psooy, K, Pike, J. “Investigation and management of antenatally detected hydronephrosis”. Can Urol Assoc J. vol. 3. 2009. pp. 69-72. (Evidence-based guidelines for the management of antenatal hydronephrosis.)

Ongoing controversies regarding etiology, diagnosis, treatment

Antenatal diagnosis of hydronephrosis is a topic still open for discussion and filled with controversies. Since it is not a disease per se, the extent of postnatal workup and intervention is largely based on the philosophy of the service treating the patient and expert opinions. There has been a trend towards being more conservative in the management of these patients, but it is still an area of ongoing change.

Main areas of controversy are summarized below and are curently being addressed by ongoing studies:

What is the ideal cutoff to consider anenatal hydronephrosis significant?

Which patients will benefit from prenatal intervention and what is the best timing for intervention? What are the long-term outcomes?

After birth, which patients, if any, need a VCUG and/or prophylactic antibiotics and/or circumcision?

What are the indications for surgery, specifically for asymptomatic UPJO?