Unilateral Renal Agenesis (Absence of One Kidney)
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The kidneys develop in the region of the urinary bladder and ascend/migrate upwards
to their location in the rear of the abdominal cavity. Most of us have 2 kidneys,
but sometimes only one can be found on ultrasound scanning.
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What is this condition and what is its significance?
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The frequency is not known precisely, but it is about 4 - 20 times that of bilateral renal agenesis. In most cases,
the kidney has not developed because of environmental rather than genetic effects
- for example, a kidney may fail to develop as a result of disrupted blood flow
to the fetus during the period when the kidneys develop in the pelvis and gradually
ascend to their correct place. Sometimes the kidney is present, but because it is
somewhat lower in the pelvis than it should be, it is difficult to see it on ultrasound.
Sometimes it is difficult to diagnose this condition because in the early weeks
of pregnancy, both the adrenal glands and intestinal loops can resemble the kidneys.
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In cases where the fetus has one normal kidney, both the amount of amniotic fluid
and the activity of the urinary bladder should be normal.
In some cases the kidney may be slightly larger than usual.
A few reports have suggested that there is a 2% risk of chromosome abnormalities
in this condition.
Also, there is an increased frequency of other defects in the urinary tract, and
therefore an ultrasound scan should be performed specifically to examine for these.
If a fetus has unilateral renal agenesis, then there is an increased risk that this
will also be found in one of the parents.
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If this is the case, the risk for recurrence is 50% in future pregnancies. The risk
relates to the absence of one or both kidneys in a future fetus.
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What should be done when this condition is diagnosed?
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Ultrasound examination
of the fetus should be performed in order to look for other defects in the urinary
tract or in other body systems. Sometimes it will become apparent during this examination
that there is a kidney situated low in the pelvis on the side on which no kidney
was previously demonstrated. Ultrasound monitoring is also required.
The parents should be referred for ultrasound scanning of their kidneys and urinary
tracts. The parents should also be referred for counseling by a clinical geneticist
in order to determine whether the unilateral renal agenesis is an isolated finding
or part of a syndrome, to ascertain whether there are other problems in addition,
and to decide on recommendations for performing special tests in addition to the
routine ones. They should also be referred to a pediatric nephrologist for counseling
about the implications for the infant in the future.
Based on the information at hand, the severity of the condition, the week of pregnancy
and other parameters, further follow-up/intervention may be considered.
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