APPROACH TO ANTENATALLY DETECTED COMMON RENAL MALFORMATIONS
Dr. M. VIJAYAKUMAR*
Consultant Pediatric Nephrologist, Chennai Pediatric Kidney Foundation, Dr. Mehta's Hospitals Pvt. Ltd., Chennai. *
Introduction
All antenatal ultrasonographic abnormalities are not documentable postnatally. Some serious antenatal renal findings are absent on postnatal evaluation. Serious thought, therefore, should be given before giving a positive or negative verdict about antenatal anomalies and approach to diagnosis and management.

Background issues

  • By 20-24 weeks renal anomalies can usually be documented by the traditional ultrasonogram.
  • Oligohydramnios indicates a urinary obstruction in the fetus especially beyond the 2nd trimester. Polyhydramnios however indicates that there is a block in the gastrointestinal tract and swallowing is affected. Polyhydramnios can also be seen antenatally with hydronephrosis.
  • Commonest finding on an antenatal scan is unilateral pelviectasis.
  • Serious defects of renal development account for 30% of CRF in children.

Who should have antenatal USG for renal anomalies?
  • High risk pregnancy
  • Assisted reproduction
  • Presence of Oligohydramnios or polyhydramnios
  • Family history suggestive of PKD
  • Previously affected baby
  • Precious baby

Common antenatal renal malformations
  1. Dilatation of pelvicalyceal system:

    1. Obstructive lesions Pelviureteric junction obstruction Posterior urethral valve disease
    2. Non obstructed refluxing lesions

    3. Vesicoureteric reflux (VUR)

      Primary (commonest)

      Associated with duplex collecting system, ectopic ureter or in the Prune-Belly syndrome.
    4. Non obstructive non refluxing lesions
    5. Primary megaureters
  2. Cystic lesions:
    • Multicystic dysplastic kidneys (MCDK) :Usually unilateral and non-inherited
    • Polycystic kidney disease :Usually bilateral. Commonly autosomal recessive. Can be autosomal dominant also
  3. Renal agenesis / hypoplasia
  4. Combined lesions like MCDK with VUR
  5. Others: Ectopic kidneys, horse-shoe kidneys.

Antenatal features suggestive of serious renal problems
  • Oligohydramnios

  • Renal cortical cysts
  • Fetal urine Na>100mEq/L,Osm>200mOsm/kg

  • Increased fetal urinary beta2 microglobulin
  • Reduced lung area or thoracic circumference suggesting pulmonary hypoplasia.

What should be the simple approach to common urological disorders?
Commonest finding of antenatal scans is unilateral pelviectasis. Unlike common ideas on this subject the cause for this is Vesicoureteric reflux and not obstruction.

When should obstruction be suspected?
  • When there is pelvi-caliectasis
  • When the AP dimension of the renal pelvis exceeds 10 mm in the 3rd trimester scan.

Probability of PUJ obstruction based on antenatal findings*
  • AP diameter of fetal renal pelvis>20mms (Most probably will lead to surgery postnatally)
  • AP diameter of fetal renal pelvis 10-20mms (Equivocal state)
  • AP diameter of fetal renal pelvis <10mm (Surgery will not be needed in most cases)
*Algorithm from Hospital for Sick Children at Great Ormond Street, London.

Uroprophylaxis in newborn
  • Ampicillin or amoxicillin or cephalexin

What will DTPA show if surgery is decided upon?
  • Delayed intrarenal transit (normal 2-4 mins)
  • Incomplete washout of tracer following frusemide (>20 mins)
  • Poor function (<40%) Surgery can be safely done after 2-3 months of age.

What will be the management if there is no evidence of obstruction on the DTPA or if DTPA is equivocal?
  • Uroprophylaxis for 6 months
  • Repeat DTPA and ultrasound
  • Annual ultrasound review till dilatation resolves

Can an equivocal DTPA become obstructive later?
Yes, in approximately 10-20%, hence the need for careful follow-up.

What should be the management if there is pelviectasis without caliectasis?
    In this case the probable diagnosis is VUR
  • Ultrasound a week after birth

  • Uroprophylaxis
  • MCU only after 3 months

Why?
  • Danger of hypothermia to newborn in X-ray department
  • Danger of urosepsis in newborn period
  • Danger of renal scarring if sepsis is introduced

Bilateral pelviectasis - Most probable diagnosis is VUR (bilateral)
  • Ultrasound a week after birth
  • Uroprophylaxis
  • MCU after 3 months

Bilateral pelvi-caliectasis with ureteral dilatation probably PUV
The antenatal ultrasound should have checked to see if the bladder cycles (fills and empties). Bladder cycling takes 15-30 minutes and this amount of time should be spent on the examination. If there is no bladder cycling it implies that there is most probably posterior urethral valve disease.

Suspected PUV - management at birth
  • Clinical examination (bladder will be palpable and urine will be passed in drops).

  • Ultrasound examination immediately looking for 'key-hole sign' which is dilatation of posterior urethra in continuity with the bladder and is almost pathognomonic of PUV.
  • MCU and immediate catheterization is mandatory.

Unilateral pelviectasis with ureteral dilatation: Possibilities
  • Primary obstructed megaureter
  • VUR
  • Duplex system obstructed by ureterocele

Management
Same as for unilateral pelviectasis.

Suspected Multicystic Dysplastic kidney detected in utero
In this case, the cysts in the kidney will be randomly arranged (in PUJ obstruction the largest cyst, namely the pelvis, will be most medial and smaller calices will be peripherally arranged).
  • Ultrasound one week after birth.
  • DMSA three months after birth to document lack of function in this kidney.
  • Contralateral kidney with PUJ or VUR (20-30%) decides the total outcome.
  • MCU to check for reflux on the opposite side three months after birth.
  • Uroprophylaxis till these studies are done.

Renal agenesis

  • Failure of development of ureteric bud results in renal agenesis. If the bud misses its target abnormal nephrogenesis is induced resulting in dysplastic kidney.
  • Unilateral renal agenesis is often associated with other organ abnormalities.
  • Bilateral renal agenesis is rare and can be detected at 12 weeks of gestational age.
  • Oligohydramnios indicates poor function and death occurs in perinatal period due to respiratory insufficiency from pulmonary hypoplasia in bilateral agenesis.
Renal dysplasia
  • Urinary tract obstruction and VUR in-utero may lead to renal dysplasia.
  • Dysplastic kidney may be solid or cystic and have variable functional impairment.

  • Extent of dysplasia and degree of urinary tract obstruction determine the clinical features of the disease.

  • Bilateral total dysplasia presents with Potter syndrome and is fatal in the neonatal period.
  • Unilateral renal dysplasia is usually asymptomatic but the contralateral kidney can have hydronephrosis or VUR.
Conclusion
By going into some of the common urological and nephrological issues in diagnosis of antenatally detected renal disease, one can be definite that no final word has been told about the approach. Experience of the sonologist, expertise of the physician involved and the co-operation of the family in question will decide the final approach. Unwanted termination is to be avoided, based on one single ultrasound finding as we know that many of these anomalies will be absent at birth. Similarly giving great hopes without knowing the background issues is also not ideal.
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