Intracranial translucency assessment at first trimester nuchal translucency ultrasound.

Introduction: The antenatal diagnosis of open spina bifida (OSB), a neural tube defect, is predominantly made at the second trimester morphology scan by ultrasound detection of structural abnormalities resulting from the associated Chiari II malformation. Evidence has emerged suggesting that these structural abnormalities can be detected earlier, by examination of the posterior fossa as part of the first trimester nuchal translucency scan. In particular, absence of the intra-cranial translucency (IT) of the fourth ventricle has shown promise as a diagnostic marker of OSB, although the sensitivity and specificity of this finding varies widely in the literature.