INTRODUCTION
Multicystic dysplastic kidney (type
II Potter) along with hydronephrosis in one of the
most commons causes of abdominal mass in the neonate.
It arises from a failure in the branching of ureteric
buds that induce nephron formation during early renal
development. Multicystic dysplastic renal disease
is the most common renal cystic disease has no association
with polycystic kidney disease (PCKD). Unlike PCKD,
multicystic dysplastic renal disease can be unilateral
or bilateral, and occurs sporadically.
A multicystic dysplastic kidney contains non-communicating multiple cystic
spaces varying in size and has no functioning renal tissue. It is always associated
with a blocked ureter (ureteric atresia). The blockage of the ureter leads
to a damming back of any urine produced within the kidney and rapidly causes
cysts to form in the renal parenchyma. If the disease is bilateral then there
will be no liquor (anhydramnios) and pulmonary hypoplasia leading to death
in early neonatal life will result. A unilateral multicystic dysplastic kidney
with good liquor volume has a good prognosis.
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ANTENATAL
Ultrasound scanning is especially
well suited to differentiating between fluid and
solid tissues, and therefore the multicystic kidney
has a high pick-up rate antenatally. The differential
diagnosis includes a hydronephrosis kidney in which
the calyces are dilated, but is distinguished by
the calyces communicating with each other via the
renal pelvis. Polycystic renal disease normally presents
as bright large kidneys and therefore is seldom confused.
Complex cystic masses in both renal fossae will point
towards multicystic renal disease as the cause, but
if the bladder is present and either dilated, or
thick walled, this would tend to suggest some form
of bladder outflow obstruction.
Multicystic dysplastic renal disease
can be bilateral, unilateral, or segmental. The size
of the cysts determines the size of the kidneys,
which can be multicystic and enlarged or shrunken,
irregular, and hyper-echogenic. Bilateral multicystic
kidneys are associated with severe oligohydramnios
and the fetal bladder will be absent on ultrasound.
If the lesion is unilateral other
anomalies should be sought, but in isolation this
anomaly, although easily seen on ultrasound scanning
is most likely to cause no major health problems
for the individual concerned. It is customary to
repeat the ultrasound examination later in pregnancy,
to look for possible pressure effects of the abdominal
mass. If one kidney is massively dilated causing
circulatory failure in the fetus, consideration may
be given to decompression or delivery. These cases
are very rare, and the most common outcome is for
the multicystic kidney to remain the same size with
the fetus and baby growing normally around it.
There is little data to suggest that
multicystic renal disease is linked to other anomalies.
The question is sometimes asked whether this finding
increases the risk of other anomalies, and a careful
search of the rest of the fetus should be part of
the assessment of the case. Most fetal medicine experts
would say that the chances of trisomy are increased,
but by how much would be debated. In a woman who
has no other risk factors and has a low risk prediction
following nuchal translucency or serum screening
the risk of invasive testing almost certainly outweighs
the risks of trisomy, but these issues may need to
be explored with the parents during the discussions
of the implications of the diagnosis.
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POSTNATAL
Severe bilateral multicystic renal
disease is incompatible with life due to the associated
oligohydramnios and pulmonary hypoplasia; these cases
should be managed conservatively. In cases where
one kidney is affected postnatal assessment can be
undertaken at any time, as the appearances are not
affected by urine output in the fetus. The affected
kidneys may be left to atrophy, however prophylactic
nephrectomy can be carried out to reduce hypertension
and the possibility of malignant change within the
remaining cystic mass. In general terms a unilateral
multicystic dysplastic kidney will be managed conservatively
whilst asymptomatic, or an increase in size.
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WEST MIDLANDS DATA
Information to follow
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