Sirenomelia with an uncommon osseous fusion associated with a neural tube defect.

A sireniform infant presented with an uncommon osseous fusion of the lower limbs characterised by a fused femur, a partially fused tibia and sympus dipus with rudimentary digits and metatarsals. Associated abnormalities included sacral agenesis, a deformed pelvis, anorectal atresia, renal agenesis, cystic renal dysplasia, agenesis of the uterus and urinary bladder, ambiguous external genitalia, a single umbilical artery, a lumbosacral neural tube defect, and ventriculomegaly secondary to a Chiari II malformation. The pathogenesis of concurrent sirenomelia and neural tube defect is discussed.