title: Three-dimensional sonography of the posterior fossa in fetuses with open spina bifida at 11-13 weeks' gestation.
abstract: OBJECTIVE
  To investigate the posterior fossa of normal fetuses and fetuses with open spina bifida in stored three-dimensional (3D) volumes and to describe signs that might allow early detection of this defect.
  
  
  METHODS
  A prospective study of 3D volumes of the fetal brain obtained from 10 normal fetuses and three fetuses with open spina bifida was undertaken. Measurements of the anteroposterior diameters of the cisterna magna and fourth ventricle were taken in the tilted axial view. In the mid-sagittal plane the brainstem (BS) diameter and the brainstem-occipital bone (BSOB) distance were measured. The BS/BSOB ratio was calculated. All measurements were expressed as Z-scores. Structural analysis of the differences in the posterior fossa between normal fetuses and fetuses with open spina bifida was undertaken.
  
  
  RESULTS
  In normal fetuses all measurements were within ±2.5 Z-scores. In three fetuses with open spina bifida the BS Z-scores were 2.7, 2.8 and 2.8; the BSOB scores were -3.4, -2.8 and -2.9; the cisterna magna scores were -5.6, -3.7 and -4.2; and the BS/BSOB ratio scores were 4.1, 9.7 and 8.9. In normal fetuses the cisterna magna was posterior to the fourth ventricle and extended along its entire length. In fetuses with open spina bifida the cisterna magna was partially or completely obliterated.
  
  
  CONCLUSIONS
  Assessment of the cranial posterior fossa is feasible at 11-13 weeks' gestation. There are distinct signs in fetuses with open spina bifida which can be evaluated by ultrasonography.
authors.affiliation: Department of Gynaecology and Obstetrics, Innsbruck Medical University, Innsbruck, Austria. matthias.scheier@uki.at
authors.forename: M
authors.initials: M
authors.lastname: Scheier
authors.forename: R
authors.initials: R
authors.lastname: Lachmann
authors.forename: M
authors.initials: M
authors.lastname: Pětroš
authors.forename: K H
authors.initials: KH
authors.lastname: Nicolaides
mesh_terms: D000005:Abdomen; D001933:Brain Stem / Q000000981:diagnostic imaging; D002946:Cisterna Magna / Q000000981:diagnostic imaging* / Q000196:embryology; D003388:Cranial Fossa, Posterior / Q000002:abnormalities / Q000000981:diagnostic imaging* / Q000196:embryology; D005240:Feasibility Studies; D005260:Female; D020546:Fourth Ventricle / Q000000981:diagnostic imaging* / Q000196:embryology; D005865:Gestational Age; D006801:Humans; D021621:Imaging, Three-Dimensional; D009777:Occipital Bone / Q000000981:diagnostic imaging; D011247:Pregnancy; D011446:Prospective Studies; D016137:Spina Bifida Cystica / Q000000981:diagnostic imaging* / Q000196:embryology; D016216:Ultrasonography, Prenatal / Q000379:methods*