Upper urinary tracts malformations (renal or ureteral) quite often can be already identified during the prenatal evaluation.
The presence of a single kidney because of the absolute lack of formation (renal agenesis) or an abnormal development of the contralateral kidney (dysplastic multicystic) must be recognized and well defined shortly after birth.
If the solitary kidney has normally developed (i.e. normal nephrological function) there are no problems and this situation is fully compatible with a perfectly normal future life.
The most frequent anatomical variant in the urinary tract is represented by a duplication of the excretion system (renal pelvis and ureter) but in the vast majority of cases this is only an incidental finding without any clinical implication.
In a small percent of cases , as for single systems, there are pathological conditions such as an obstruction, an ectopic ending or a terminal dilatation of the ureter (ureterocele).
In these situations it is not infrequent the association with a retrogrede back-flow of urine in the upper tracts (vesico-ureteric reflux VUR ) and/or urinary tracts infections (UTI) – see also section 4
Finally there are renal anomalies of position with the kidney being located not in the usual lumbar place (ectopia) or of fusion (horse-shoe, pancake kidney) because of a partial or complete attachment of the renal poles. In these cases as well it can be only an incidental finding without pathological or harmful implications.