Congenital disorders of the kidney
Congenital malformations of the kidney
Congenital malformations of the kidney are not uncommonly found on antenatal screening and in newborns.
Often associated with other congenital abnormalities and the risk is higher in those with a previous family history. Chromosomal abnormalities account for a proportion, but most are sporadic.
The fetal kidneys develop when the ureteric bud comes into contact with the metanephric blastema caudally (in the ‘pelvic’ area), signalling it to form nephrons and the collecting system. This forms the ‘metanephros’, which becomes a functioning kidney and begins to produce urine by around 11 weeks. By 14–16 weeks, most of the amniotic fluid consists of fetal urine. Then the kidneys have to migrate rostrally, to lie in the lumbar region.
If the ureteric bud fails to develop properly, the ureter and kidney do not develop.
Bilateral agenesis is rare and incompatible with life. It may present with oligohydramnios. About 50% occur as part of Potter syndrome with a flattened facies, limb deformities and hypoplastic lungs, sometimes with developmental abnormalities of other organs.
Unilateral agenesis is much more common and associated with other renal abnormalities such as reflux or strictures and unicornuate uterus. In some cases, the kidney may develop abnormally, with multiple cysts, then regress before or soon after birth. The remaining kidney undergoes compensatory hypertrophy. Some develop proteinuria later in life due to progressive glomerulosclerosis, occasionally leading to renal failure. However, the prognosis for these patients is excellent with no reduction in life expectancy.
Simple renal hypoplasia is when the kidney is smaller than normal, but the structure and histology of the kidney is normal, although the nephrons may be slightly small.
Oligonephronic renal hypoplasia (also called oligo-meganephronia) is when there are far fewer nephrons than normal (about a quarter the usual number), fewer renal papillae and microscopy shows abnormally enlarged glomeruli and nephrons. The prognosis is poor for these patients, although there may be some initial improvement in renal function over the first few years of life, they develop progressive focal glomerulosclerosis with proteinuria and end stage renal failure.
The kidney develops abnormally with primitive tubules and cartilagenous components.
· Horseshoe kidney – the kidneys remain fused at the upper (10%) or lower (90%) poles to form a horseshoe-shaped structure. Rarely, they remain fused at both poles to form a discoid kidney.
· Ectopic kidney – one or both of the kidneys may remain in the pelvis, or one of the kidneys may migrate to the other side.
These anatomical abnormalities may be symptomless, or problems with the flow of urine can cause obstructive uropathy and predisposition to urinary stones and infections. In pregnancy, low pelvic kidneys can interfere with labour. They are diagnosed by IVU or renal USS.
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