Measurement of compensatory hyperplasia of the contralateral kidney: usefulness for differential diagnosis of fetal unilateral empty renal fossa.

OBJECTIVE

To assess the usefulness of sonographic evaluation of compensatory hyperplasia of the contralateral kidney for the differential diagnosis of fetal unilateral empty renal fossa (ERF).

METHODS

We retrospectively measured the ratio of the anteroposterior (AP) and transverse (TR) diameters of the contralateral kidney in 24 fetuses with unilateral ERF including 12 cases of unilateral renal agenesis, six cases of a unilateral pelvic kidney and six cases of a unilateral ectopic multicystic dysplastic kidney (MCDK). For the normal reference value, we calculated the AP : TR diameter ratios of both kidneys in 20 normal fetuses in the second and third trimesters. We calculated the accuracy of the AP : TR ratio to detect contralateral compensatory hyperplasia.

RESULTS

The median (range) AP : TR diameter ratios of the normal kidneys were 0.84 (0.72-0.89) in the second trimester and 0.81 (0.65-0.89) in the third trimester. All cases of unilateral renal agenesis and ectopic MCDK showed the presence of compensatory hyperplasia, while no case of renal ectopy was seen with compensatory hyperplasia. The median (range) ratios for unilateral renal agenesis and ectopic MCDK were 1.0 (0.95-1.02) and 1.1 (1-1.25) in the second and third trimesters, respectively. The median ratios for a unilateral pelvic kidney were 0.8 (0.74-0.85) and 0.77 (0.74-0.84) in the second and third trimesters, respectively. Using 0.9 as the discriminating value, the sensitivity, specificity, and accuracy of the AP : TR diameter ratio for the prenatal diagnosis of compensatory renal hyperplasia was 100%.

CONCLUSION

Sonographic evaluation of compensatory hyperplasia of the contralateral kidney may be useful for the differential diagnosis of a fetal unilateral ERF. Prospective studies are warranted.