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260 Chapter 6: Genitourinary system

for the renal failure, and plasma exchange is used for occur as part of Potter syndrome with a flattened fa-
persistent or severe cases. cies, limb deformities and hypoplastic lungs, some-
Plasma exchange appears to correct the coagula- times with developmental abnormalities of other
tion/platelet abnormalities, either by replacing the lost organs.
vWF cleaving protease or removing the antibodies, or Unilateral agenesis is much more common and asso-
both. ciated with other renal abnormalities such as reflux or
Platelet transfusions should be avoided unless there is strictures and unicornuate uterus. In some cases, the
severe bleeding, as they may exacerbate the condition. kidney may develop abnormally, with multiple cysts,
then regress before or soon after birth. The remaining
Prognosis kidney undergoes compensatory hypertrophy. Some
This has markedly improved with the advent of plasma develop proteinuria later in life due to progressive
exchange. Chronic renal failure occurs in a substantial glomerulosclerosis, occasionally leading to renal fail-
number of patients. ure. However, the prognosis for these patients is ex-
cellent with no reduction in life expectancy.

Congenital disorders of the kidney
Renal hypoplasia
Congenital malformations of the Simple renal hypoplasia is when the kidney is smaller
kidney than normal, but the structure and histology of the
kidney is normal, although the nephrons may be
Definition slightly small.
Congenital malformations of the kidney are not uncom- Oligonephronic renal hypoplasia (also called oligo-
monly found on antenatal screening and in newborns. meganephronia) is when there are far fewer nephrons
than normal (about a quarter the usual number),
Aetiology fewer renal papillae and microscopy shows abnor-
Often associated with other congenital abnormalities mally enlarged glomeruli and nephrons. The prog-
and the risk is higher in those with a previous family nosis is poor for these patients, although there may
history. Chromosomal abnormalities account for a pro- be some initial improvement in renal function over
portion, but most are sporadic. the first few years of life, they develop progressive fo-
cal glomerulosclerosis with proteinuria and end stage
renal failure.
Normal fetal kidney development
The fetal kidneys develop when the ureteric bud comes
into contact with the metanephric blastema caudally Dysplasia (failure of differentiation)
(in the ‘pelvic’ area), signalling it to form nephrons The kidney develops abnormally with primitive tubules
and the collecting system. This forms the ‘metanephros’, and cartilagenous components.
which becomes a functioning kidney and begins to pro- Abnormal migration of the kidneys:
duce urine by around 11 weeks. By 14–16 weeks, most Horseshoe kidney – the kidneys remain fused at
of the amniotic fluid consists of fetal urine. Then the the upper (10%) or lower (90%) poles to form a
kidneys have to migrate rostrally, to lie in the lumbar horseshoe-shapedstructure.Rarely,theyremainfused
region. at both poles to form a discoid kidney.
Ectopic kidney – one or both of the kidneys may re-

Renal agenesis main in the pelvis, or one of the kidneys may migrate
If the ureteric bud fails to develop properly, the ureter to the other side.
and kidney do not develop. These anatomical abnormalities may be symptomless,
Bilateral agenesis is rare and incompatible with life. or problems with the flow of urine can cause obstruc-

It may present with oligohydramnios. About 50% tive uropathy and predisposition to urinary stones and