CYSTIC KIDNEY DISEASE

Cystic kidney disease
Congenital cystic kidney disease can be classified into genetic and non-genetic types.
Genetic
- Autosomal recessive polycystic kidney disease (ARPKD)
A disease of infancy and childhood, where renal collecting tubules and ducts become cystically dilated and numerous small cysts form in the renal cortex and medulla. Severe forms present early and have a poor prognosis. Prenatal USS demonstrates oligohydramnios (amniotic fluid <200ml) and large, ‘bright  homogeneously hyperechogenic kidneys, which can cause obstructed labour and respiratory problems. Neonates have large flank masses, limb and facial anomalies. All cases are associated with congenital hepatic fibrosis. Infants develop fatal uraemia and respiratory failure; older children present with renal failure, hypertension, and portal hypertension. Most develop end-stage renal failure by adulthood, requiring haemodialysis and renal transplantation.

- Autosomal dominant polycystic kidney disease (ADKD)
Typically presents in adulthood, although older children can present with complications of haematuria, flank pain, flank mass, UTI, proteinuria, hypertension, and intracerebral bleeds (secondary to berry aneurysm rupture). It is characterized by multiple expanding cysts of both kidneys that ultimately destroy the intervening parenchyma, and accounts for 10% of all chronic renal failure.

- Familial juvenile nephronophthisis
An autosomal recessive disorder which develops in early childhood and accounts for up to 20% of paediatric renal failure. Medullary cystic disease is a similar (autosomal dominant) condition which develops in later childhood. Histology shows interstitial nephritis associated with medullary and corticomedullary cysts. Disease progression causes a reduction in kidney size. Features include polyuria, polydipsia, anaemia, growth retardation, and chronic renal failure.
Renal cysts are also a feature of autosomal dominant conditions including Von Hippel Lindau syndrome (cerebellar haemangioblastomas, phaeochromocytoma, renal cell carcinoma) and tuberous sclerosis (adenoma sebaceum, epilepsy, learning difficulties).

Non-genetic
- Multicystic dysplastic kidney
The most common cystic kidney disorder. The cysts of a ‘multicystic  kidney are not due to dilatation of renal collecting ducts (as in polycystic disease) but, instead, the entire kidney is dysplastic, with immature dysplastic stroma and cysts of various sizes. Bilateral disease is incompatible with life. Unilateral disease is often associated with reflux or PUJ obstruction in the contralateral kidney. Affected kidneys may undergo renal aplasia, where they spontaneously shrink to a tiny remnant. USS and renograms (DMSA) help to distinguish this condition from hydronephrosis. Most can be treated conservatively with close surveillance for the associated risks of hypertension and Wilms  tumour, which would be indications for surgery.

- Multilocular cystic nephroma
Presents in young children with a flank mass. It is included in a spectrum of disease that is closely associated with Wilms  tumour, and so the recommended treatment is partial or full nephrectomy.