Multicystic dysplastic kidney

Congenital malformation of a kidney in which multiple noncommunicating cysts replace normal renal tissue, rendering the organ nonfunctional.

• Most common cystic kidney disease in infants; a key cause of a flank mass in newborns. Unilateral MCDK highlights management of a child with a single kidney, whereas bilateral MCDK causes Potter sequence (fatal), making early recognition crucial.

• Often detected on prenatal ultrasound as a unilateral cystic kidney; if missed in utero, a newborn may present with an asymptomatic flank mass.
• Bilateral MCDK leads to oligohydramnios → Potter sequence (lung hypoplasia, flat facies, limb deformities; usually fatal).
• Associated urinary tract anomalies are common – e.g. contralateral vesicoureteral reflux or other CAKUT – so the normal kidney may show signs of reflux or obstruction.
• If one kidney is affected, the other kidney hypertrophies to compensate; children with unilateral MCDK generally have normal renal function due to the healthy kidney.

1. Confirm diagnosis with postnatal renal ultrasound and evaluate the contralateral kidney (e.g. perform a voiding cystourethrogram to check for reflux).
2. In unilateral MCDK, management is conservative: regular follow-up with ultrasound and blood pressure monitoring, since most dysplastic kidneys undergo spontaneous involution.
3. Avoid immediate nephrectomy unless complications arise – observe unless there is problematic hypertension, recurrent UTIs, or a suspicion of malignancy in the dysplastic kidney.
4. Bilateral MCDK requires neonatal intensive care and nephrology consultation. If any renal function is present, dialysis may be initiated as a bridge to possible transplant, though prognosis is poor.

1. Unilateral MCDK: observe and monitor – periodic ultrasounds and blood pressure checks, as the cystic kidney usually regresses over time.
2. No intervention is needed unless there are complications. If the dysplastic kidney causes issues (e.g. persistent hypertension or infections), surgical nephrectomy can be considered.
3. Bilateral MCDK: primarily supportive care – manage respiratory failure at birth, consider dialysis; renal transplant would be the only definitive treatment if the infant survives long enough.

• Ultrasound appearance is like a “cluster of grapes” instead of a kidney – a classic clue for MCDK (especially if unilateral). If both kidneys are replaced by “grapes,” the fetus will have Potter sequence.

• Bilateral MCDK → Potter sequence (oligohydramnios leading to pulmonary hypoplasia) – a neonatal emergency that is usually incompatible with life.
• In a child with known MCDK, new-onset hypertension, UTI, or abdominal pain warrants prompt evaluation – the dysplastic kidney may need removal to prevent further harm.

1. Suspected MCDK on prenatal ultrasound → plan postnatal ultrasound to confirm and check both kidneys.
2. If confirmed MCDK: assess contralateral kidney function and do VCUG to rule out reflux in the healthy kidney.
3. Unilateral MCDK → routine follow-up (renal ultrasounds, BP monitoring, renal function tests). Protect the solitary functioning kidney (avoid nephrotoxins, counsel on hydration and sports).
4. Bilateral MCDK → immediate supportive management at birth (airway and breathing support due to lung hypoplasia). If possible, initiate dialysis and discuss renal transplant options.

• Newborn with a unilateral flank mass on exam; ultrasound shows multiple non-communicating cysts in one kidney → Multicystic dysplastic kidney (unilateral).
• Prenatal ultrasound reveals bilateral large, cystic kidneys with oligohydramnios; neonate is born with respiratory distress (Potter sequence) → Bilateral MCDK (lethal).
• Prenatal ultrasound finds one kidney filled with cysts but normal amniotic fluid volume; the infant is born healthy with normal urine output → Unilateral MCDK, best managed with observation.