[Empty renal fossa--a prenatal diagnostic dilemma]

To assess the feasibility of ultrasound for the prenatal diagnosis and the evaluation of prognosis in cases with empty fetal renal fossa.

A prospective observational longitudinal study from September 2007 till May 2010 was performed with high-resolution ultrasound equipment at MC "MARKOVS" and State University Hospital of Ob/Gyne "Maichin dom", Sofia. Seventeen cases with empty fetal renal fossa (EFRF) were prenatally diagnosed. Renal ectopia or unilateral renal agenesis (URA) were the two major differential diagnoses. Cases with bilateral renal agenesis were excluded from further analysis. The following prognostic factors were analyzed: gestational age at diagnosis, type and location of the defect, obstruction of the urinary tract and presence of associated structural fetal abnormalities. Invasive prenatal diagnosis (genetic amniocentesis) and fetal karyotyping was offered if required. Termination of pregnancy was an option in cases diagnosed at earlier gestational age with pessimistic prognosis. All continuing pregnancies were followed-up sonographically, incl. with fetal echocardiography. Pregnancy outcome was ascertained from hospital records, referring physicians and/or the patients themselves.

Overall 17 cases with EFRF were prenatally diagnosed during the study period. The mean gestational age at diagnosis was 22+3 w.g. Prenatal detection of EFRF before 24 w.g. was achieved in 82 (14/17). There were 9 cases of ectopic kidney: 7--pelvic, 1--iliac, 1--crossed fused ectopia. The remaining 8 cases had URA. Empty fetal renal fossa was an isolated finding in 16/17 cases. In the last 17th case the anomaly was part of a malformation complex associated with tetralogy of Fallot and single umbilical artery. No cases with urinary tract obstruction were observed. In 16/17 cases there was favorable perinatal outcome. The remaining pregnancy with associated anomalies was terminated. There was one case with missed diagnosis of URA, detected after birth during an abdominal scan performed for another reason.

Ultrasound is the method of choice for prenatal diagnosis and prognostic evaluation in cases with EFRF. Early detection allows adequate consultation and pregnancy follow-up. In cases with associated anomalies termination of pregnancy is an option. All continuing pregnancies with EFRF generally have good prognosis and favorable perinatal outcome.