title: Intracranial translucency assessment at first trimester nuchal translucency ultrasound.
abstract: BACKGROUND
  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. The aim of this study is to assess the feasibility of obtaining the image of the IT at our institution as part of the routine first trimester scan.
  
  
  METHODS
  This is a prospective study of 900 obstetric patients who presented to a tertiary women's imaging centre for routine first trimester nuchal translucency screening ultrasound for the year 2014. Their risk status was that of the general population (low risk) prior to presentation. A total of 158 patients were excluded, leaving a study group of 742. Sonographers obtained a mid-sagittal view of the fetal face with particular focus on optimum viewing of the IT. All images were examined by a Radiology Registrar for presence or absence of IT. Duration of each scan was documented.
  
  
  RESULTS
  The IT image was successfully acquired in 94.9% of scans. Maternal pre-pregnancy BMI and fetal lie were shown to have a statistically significant effect on success of acquisition of the IT image. No cases of OSB were diagnosed during the study. Scan times were not lengthened by the addition of the image.
  
  
  CONCLUSIONS
  We consider that acquisition of an image of the IT as part of the routine first trimester nuchal translucency scan is feasible, without lengthening appointment times.
authors.affiliation: Department of Medical Imaging, Royal Brisbane and Women's Hospital, Brisbane, Queensland, Australia.
authors.forename: Annah
authors.initials: A
authors.lastname: Lane
authors.affiliation: Department of Medical Imaging, Royal Brisbane and Women's Hospital, Brisbane, Queensland, Australia.
authors.forename: Ling
authors.initials: L
authors.lastname: Lee
authors.affiliation: Department of Medical Imaging, Royal Brisbane and Women's Hospital, Brisbane, Queensland, Australia.
authors.forename: Donna
authors.initials: D
authors.lastname: Traves
authors.affiliation: Department of Medical Imaging, Royal Brisbane and Women's Hospital, Brisbane, Queensland, Australia.
authors.forename: Andreas
authors.initials: A
authors.lastname: Lee
mesh_terms: D000293:Adolescent; D000328:Adult; D005260:Female; D006801:Humans; D048208:Nuchal Translucency Measurement; D011247:Pregnancy; D011261:Pregnancy Trimester, First; D011446:Prospective Studies; D012680:Sensitivity and Specificity; D016135:Spinal Dysraphism / Q000000981:diagnostic imaging*; D016216:Ultrasonography, Prenatal / Q000379:methods*
keywords: obstetric ultrasound