title: Normal morphometry of fetal posterior fossa at midtrimester: brainstem-tentorium angle and brainstem-vermis angle.
abstract: OBJECTIVE
  To standardize the evaluation of normal tentorium insertion and normal rotation of the cerebellar vermis over the brainstem, using two novel measurements: the brainstem-tentorium angle (BT angle) and the brainstem-vermis angle (BV angle). We also aimed to test the reproducibility of these measurements.
  
  
  METHODS
  Prospective observational study including normal fetuses at routine anomaly scan with confirmed normal follow-up. Three-dimensional volumes of the fetal head were acquired starting from standard trans-cerebellar views. In the sagittal plane, obtained by multiplanar reconstruction, the angle between the brainstem and the tentorium insertion in the fetal skull, and between the brainstem and the lower edge of the vermis were measured twice by two independent operators. Intraobserver and interobserver variations were calculated.
  
  
  RESULTS
  Eighty cases were included. The estimated BT and BV angles lie in a wide interval among normal midtrimester fetuses with a median value (min-max) of 25.65 (20.13-47.39) and 9.29 (3.87-19.36) respectively. Intraobserver and interobserver variation were good for both measurements.
  
  
  CONCLUSIONS
  The BT and BV angle may be of help in assessing the fetal posterior fossa at midgestation and gives a standardized and reproducible measurement of normal tentorium insertion and normal rotation of the cerebellar vermis over the brainstem.
authors.affiliation: Department of Obstetrics and Gynaecology, St. Orsola Malpighi Hospital, University of Bologna, Bologna, Italy. tullioghi@yahoo.com
authors.forename: Tullio
authors.initials: T
authors.lastname: Ghi
authors.forename: Elena
authors.initials: E
authors.lastname: Contro
authors.forename: Francesca
authors.initials: F
authors.lastname: De Musso
authors.forename: Antonio
authors.initials: A
authors.lastname: Farina
authors.forename: Roberto
authors.initials: R
authors.lastname: Conturso
authors.forename: Paola
authors.initials: P
authors.lastname: Bonasoni
authors.forename: Ginevra
authors.initials: G
authors.lastname: Salsi
authors.forename: Aly
authors.initials: A
authors.lastname: Youssef
authors.forename: Nicola
authors.initials: N
authors.lastname: Rizzo
authors.forename: Gianluigi
authors.initials: G
authors.lastname: Pilu
mesh_terms: D001933:Brain Stem / Q000000981:diagnostic imaging*; D005260:Female; D006801:Humans; D021621:Imaging, Three-Dimensional; D011247:Pregnancy; D011446:Prospective Studies; D015203:Reproducibility of Results; D016216:Ultrasonography, Prenatal