Prenatal diagnoses in unilateral empty renal fossa.

Six cases of unilateral empty renal fossa diagnosed by obstetric sonography are described. The anomalies reported (ectopic kidney, cross-fused ectopic kidney, and unilateral renal agenesis) have not yet been described in the prenatal literature, to our knowledge, in fetuses that are otherwise normal. The study also demonstrates that, in spite of their nonvital in utero role, single kidneys may show compensatory hypertrophy.