title: Fetal posterior fossa dimensions: normal and anomalous development assessed in mid-sagittal cranial plane by three-dimensional multiplanar sonography.
abstract: OBJECTIVE
  To construct nomograms of the dimensions of the fetal posterior fossa (PF), assessed in the mid-sagittal plane in the second and third trimesters, and to assess how measurements from fetuses with PF abnormalities deviate from our normal ranges.
  
  
  METHODS
  This was a prospective cross-sectional study of 378 healthy fetuses in low-risk singleton pregnancies between 15 and 35 weeks. PF size was evaluated in the mid-sagittal plane of the fetal head using three-dimensional multiplanar reconstruction (3D-MPR). The borders of the PF were defined from the clivus to the tentorium (clivotentorial distance, CTD) and from the occipital bone to the level of the upper mesencephalic edge (tecto-occipital distance, TOD), and the posterior fossa area (PFA) and perimeter (PFP) were assessed. Growth charts were produced. Thirty-nine fetuses diagnosed with PF malformations were analyzed by calculating the z-scores of PFA, PFP, TOD and CTD, relative to the developed nomograms.
  
  
  RESULTS
  Of the 378 healthy fetuses initially included, there were 281 with adequate visualization of the PF borders; i.e. PF mid-sagittal plane morphometry was feasible in 74.3% of cases. There was a linear relationship between each of PFA, PFP, TOD and CTD, and gestational age, with Pearson correlation coefficients of 0.97, 0.97, 0.96 and 0.95, respectively (P < 0.001 for each). Chiari II malformation (CM-II) and Dandy-Walker malformation (DWM) were associated with the greatest difference in PF size compared with normal; PFA z-scores exceeded 2.6 in all five DWM cases and were below -2.66 in all 11 CM-II cases.
  
  
  CONCLUSIONS
  Sonographic evaluation of fetal PF size in the mid-sagittal plane is feasible. Our constructed nomograms provide reference data that may be helpful when evaluating PF congenital malformations.
authors.affiliation: Division of Prenatal Diagnosis, Department of Obstetrics and Gynecology, Wolfson Medical Center, Holon, Israel.
authors.forename: Z
authors.initials: Z
authors.lastname: Leibovitz
authors.forename: K K
authors.initials: KK
authors.lastname: Haratz
authors.forename: G
authors.initials: G
authors.lastname: Malinger
authors.forename: I
authors.initials: I
authors.lastname: Shapiro
authors.forename: C
authors.initials: C
authors.lastname: Pressman
mesh_terms: D001139:Arnold-Chiari Malformation / Q000000981:diagnostic imaging; D003388:Cranial Fossa, Posterior / Q000000981:diagnostic imaging*; D003430:Cross-Sectional Studies; D003616:Dandy-Walker Syndrome / Q000000981:diagnostic imaging; D005260:Female; D005865:Gestational Age; D057238:Growth Charts; D006801:Humans; D021621:Imaging, Three-Dimensional / Q000379:methods*; D049451:Nomograms; D011247:Pregnancy; D011262:Pregnancy Trimester, Second; D011263:Pregnancy Trimester, Third; D011296:Prenatal Diagnosis / Q000379:methods*; D011446:Prospective Studies; D016216:Ultrasonography, Prenatal / Q000379:methods*
keywords: 3D ultrasound; Chiari malformation; Dandy-Walker malformation; clivotentorial distance; fetus; tecto-occipital distance