Fetal pelvi-ureteric junction obstruction: predictors of outcome.

Objective: To examine the relationship between pre-natal ultrasonographic findings typical of pelvi-ureteric junction (PUJ) obstruction and post-natal renal function in the affected kidney.
Patients and Methods: This retrospective study comprised 35 infants in whom pre-natal ultrasonography had identified a unilateral pattern of dilatation of the renal pelvis and calices typical of PUJ obstruction. In each case, the presence of unilateral hydronephrosis had been confirmed post-natally by ultrasonography, and differential function and drainage evaluated by isotope renography. The results of isotope renography were compared with the severity and timing of onset of the fetal hydronephrosis.
Results: Eleven kidneys (31%) appeared normal in the second trimester and dilatation only became apparent during the third trimester. Mean differential function in these kidneys was 48%. However, mean differential function was reduced (mean 38%) in those kidneys noted to be dilated between 16 and 24 weeks gestation. Differential function was loosely correlated with the severity of dilatation in early onset cases, i.e. the mean differential function was 42% for mild, 37% for moderate and 27% for severe dilatation. A considerable variation in differential function values was present in each group except for those with severe dilatation, which was a significant predictor of poor functional outcome when compared with mild and moderate dilatation combined (P < 0.01).
Conclusion: Fetal PUJ obstruction is a heterogeneous condition permitting only broad predictions of functional outcome. Severe dilatation detected on second trimester imaging predicted significant loss of function. Mild and moderate degrees of dilatation were associated with a one in three risk of functional impairment in the obstructed kidney.