A 26-year-old woman, primigravida, was scanned for the first time at 12 weeks of gestation. A twin mono-amniotic pregnancy was visualized. At 16 weeks, a cystic mass was diagnosed in the pelvis of one of the twins. There was also a single umbilical artery. The other twin showed no abnormalities. An amniocentesis was performed (normal karyotype 46 XY).

At 24 weeks, the malformation was confirmed. The two kidneys had physiological pyelocaliceal dilatation. A hypospadias was seen with bilateral cryptorchid. There was any abdominal wall malformation. The spine was normal. An urogenital complex anomaly was suspected by the pediatric surgeon, and particularly a cloaca dysgenesis was suggested to be the diagnosis.

At 32 weeks, the pelvic mass had increased and the cyst became multilobulated. At 36 weeks, a vaginal delivery occurred (2020g, Apgar 0). The first twin died after 15 minutes due to pulmonary hypoplasia. The second baby was healthy.

Concerning to the first baby, this fetus radiography was normal. The parents refused an anatomic-pathological examination. The baby presented with several external anomalies as:

• Anal imperforation
• Hypospadias with bilateral cryptorchidy
• Prominent abdomen
• Cloaca dysgenesis

The final diagnosis was cloaca dysgenesis with imperforate anus.

Transverse view at 24 weeks showing a pelvis cyst and normal kidney with physiological pyelocaliceal dilatation

View of the pelvic cyst at 24 weeks (on the left) and  34 weeks (on the right)

3D view of the pelvis at 24 weeks

Left image: Transverse view of pelvis at 34 weeks. Right image: Transverse view of the stomach at 31 weeks

Visualization of the sex of the twins. Note the hypospadias of the first twin