Comparison of six sonographic signs in the prenatal diagnosis of spina bifida.

AIMS: To compare the diagnostic accuracy of sonographic signs that may be looked for in fetuses with spina bifida.

METHODS: Forty-nine fetuses affected by spina bifida were enrolled, at a gestational age of 18-28 weeks. The following sonographic signs were looked for: "lemon" sign, small cerebellum, effaced cisterna magna, small posterior fossa, ventriculomegaly and direct visualization of a spinal defect.

RESULTS: The "lemon" sign was present in 53%, a small cerebellum in 96%, an effaced cisterna magna in 93%, a small posterior fossa in 96%. Ventriculomegaly was present in 40/49 (81%) cases and was severe in 20 fetuses and borderline in the remaining 20. The spinal defect was missed in one fetus presenting the cerebellar and posterior fossa signs. In two fetuses, the myelomeningocele was present without cranial signs of Chiari II malformation and in both cases the defect was covered by intact skin.

CONCLUSIONS: Our results confirm the usefulness of evaluation of the posterior fossa in the diagnosis of spina bifida, particularly in cases of small spinal defects that may be missed at ultrasound. Conversely, myelomeningocele covered by intact skin was not associated with the cranial signs of Chiari II malformation.