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Renal agenesis or aplasia
Kidneys failed to form or develop
is a relatively rare anomaly occurring in approximately 1 in 1000 live births and is more common in males than females.
can be detected by prenatal sonography, and it generally manifests as absence of a kidney on one side (unilaterally) and an associated unusually large kidney on the other side (compensatory hypertrophy)
Supernumerary kidney
which is also relatively rare, involves the presence of a third, small, rudimentary kidney.
It has no parenchymal attachment to a kidney, and in about half the cases, the supernumerary kidney drains from an independent renal pelvis into the ureter on that side.
It often becomes symptomatic as a result of infection.
Hypoplasia
is a rare anomaly of size involving a kidney that is developed less than normally in size but contains normal nephrons
Usually, is associated with hyperplasia of the other kidney.
Hyperplasia
it involves overdevelopment of a kidney.