Prevalence:

• 1 in 400 births.
• More common in male fetuses.

Ultrasound diagnosis:

• 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.

Associated abnormalities:

• 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.

Investigations:

• Detailed ultrasound examination.

Follow up:

• Ultrasound scans every 4 weeks to detect possible late-onset hydronephrosis.

Delivery:

• Standard obstetric care and delivery.

Prognosis:

• In isolated forms, the prognosis is good. Postnatal follow-up is advised because of significant risk of infections, hydronephrosis and nephrolithiasis (70%).

Recurrence:

• Isolated or part of Turner syndrome: no increased risk.
• Part of trisomy 18: 1%.