- 1 in 400 births.
- More common in male fetuses.
- Fusion of the lower poles of both kidneys in front of the descending aorta.
- Horseshoe kidney is best demonstrated on the coronal and transverse scans when renal tissue will be seen crossing the midline.
- Normal bladder and amniotic fluid volume.
- Chromosomal abnormalities: horseshoe kidney is found in 30% of cases of Turner syndrome and in 20% of trisomy 18.
- Associated syndromes are found in 15% of cases. The most common is Caudal regression syndrome (sporadic; sacral agenesis or hypoplasia, hypoplastic veretebral bodies, anal atresia).
- Other defects include hydronephrosis, and genital anomalies.
- Extra-renal defects, mainly CNS, cardiac or skeletal, are found in 30% of cases.
- Detailed ultrasound examination.
- Ultrasound scans every 4 weeks to detect possible late-onset hydronephrosis.
- Standard obstetric care and delivery.
- In isolated forms, the prognosis is good. Postnatal follow-up is advised because of significant risk of infections, hydronephrosis and nephrolithiasis (70%).
- Isolated or part of Turner syndrome: no increased risk.
- Part of trisomy 18: 1%.