Prevalence:

• 1 in 1,000 births.

Ultrasound diagnosis:

• The kidneys are replaced by multiple irregular cysts of variable size with intervening hyperechogenic stroma.
• Renal pelvis cannot be visualised.
• The disorder can be unilateral (80% of cases), bilateral or segmental; if bilateral, there is associated anhydramnios and the bladder is ‘absent’.
• Abnormalities of the contralateral kidney (25%): duplex system, pelvico-uretric obstruction, agenesis, ectopic or affected by vesico-ureteric reflux.

Associated abnormalities:

• Chromosomal defects, mainly trisomy 18, are found in 3% of unilateral lesions and 15% of bilateral ones.
• Associated syndromes are found in 10% of cases. The most common are: Brachio-otorenal syndrome (autosomal dominant; brachial cyst presenting as anterolateral neck cyst, multicystic kidneys), VACTERL association (sporadic; vertebral and ventricular septal defects, anal atresia, tracheoesophageal fistula, renal anomalies, radial dysplasia and single umbilical artery), Short-rib polydactyly syndrome (autosomal recessive; short limbs, hypoplastic thorax, polydactyly, heart  and brain defects, multicystic kidneys), Meckel-Gruber syndrome (autosomal recessive; polydactyly, multicystic kidneys, occipital cephalocele).
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Investigations:

• Detailed ultrasound examination.
• Karyotyping might be useful in case of bilateral form or associated with other abnormalities
  to estimate the risk of recurrence.

Follow up:

• Unilateral: Ultrasound scans every 4 weeks to detect possible late-onset hydronephrosis.
• Bilateral: if the pregnancy continues then follow-up should be standard.

Delivery:

• Standard obstetric care and delivery.

Prognosis:

• Bilateral: lethal either in utero or in the neonatal period due to pulmonary hypoplasia.
• Unilateral: normal prognosis. Postnatally, most urologists adopt an expectant approach because the kidney gradually shrinks and may disappear. The parents and family should also be scanned to exclude autosomal dominant branchio-otorenal syndrome.

Recurrence:

• Isolated: 1-2%.