Objective: The study aimed to describe reference values for structures of the posterior fossa in fetuses with a crown-rump length (CRL) between 45 and 84 mm. Materials and Methods: This was a prospective, cross-sectional study including 216 normal appearing fetuses. In transvaginal acquired 3-dimensional volume blocks, the longest diameter of the vermis (VE), posterior membranous area (PMA), medulla-oblongata-pons angle (MOPA), diameters of the medulla oblongata (MO) and pons (PO), and the area of Blake’s pouch (BP) were measured. Polynomial or linear regression analysis were performed to calculate the mean, 5th and 95th centile according to CRL. In 20 fetuses, intra- and interobserver repeatability were calculated. Results: There is a curvilinear correlation between CRL and PO (PO [mean] = 1.3893 + 0.004356 × CRL + 0.000002610 × CRL3; SD = 1.6818 – 0.03765 × CRL + 0.000003831 × CRL3; R2 = 0.489); CRL and MO (MO [mean] = 1.5959–0.001905 × CRL + 0.000003362*CRL3; SD = –0.1417 + 0.005404 × CRL + 0.0000004988 × CRL3; R2 = 0.525); CRL and VE (VE [mean] = –0.3640 + 0.04302 × CRL+ 0.000001486 × CRL3; SD = 0.5854 – 0.004812 × CRL + 0.0000005896 × CRL3; R2 = 0.643); CRL and PMA (PMA [mean] = 0.6901 + 0.04307 × CRL – 0.0000008459 × CRL3; SD = –0.4232 + 0.02026 × CRL – 0.000001320 × CRL3; R2 = 0.272); CRL and BP (mm2; BP [mean] –12.2067 + 0.3334 × CRL – 0.00001262 × CRL3; SD = –1.6431 + 0.06380 × CRL+ 0.0000003257 × CRL3; R2 = 0.289). The relation between CRL and MOPA (°) is best described by a linear regression (MOPA [mean] = 79.6332 + 0.6122 × CRL; SD = 4.8453 + 0.07333 × CRL; R2 = 0.318). Conclusion: We provide reference values for anatomical structures of the posterior fossa of fetuses between 45 and 84 mm CRL. The established reference values might ease the diagnosis of fetal malformations in early pregnancy.

Hernadi L, Torocsik M: Screening for fetal anomalies in the 12th week of pregnancy by transvaginal sonography in an unselected population. Prenat Diagn 1997; 17: 753–759.
Economides DL, Braithwaite JM: First trimester ultrasonographic diagnosis of fetal structural abnormalities in a low risk population. Br J Obstet Gynaecol 1998; 105: 53–57.
Carvalho MH, Brizot ML, Lopes LM, Chiba CH, Miyadahira S, Zugaib M: Detection of fetal structural abnormalities at the 11–14 week ultrasound scan. Prenat Diagn 2002; 22: 1–4.
Syngelaki A, Chelemen T, Dagklis T, Allan L, Nicolaides KH: Challenges in the diagnosis of fetal non-chromosomal abnormalities at 11–13 weeks. Prenat Diagn 2011; 31: 90–102.
Jorgensen DE, Vejlstrup N, Jorgensen C, Maroun LL, Steensberg J, Hessellund A, Jorgensen FS, Larsen T, Shalmi AC, Skibsted L, Zingenberg H, Ekelund C, Tabor A: Prenatal detection of congenital heart disease in a low risk population undergoing first and second trimester screening. Prenat Diagn 2015; 35: 325–330.
Altmann R, Scharnreitner I, Scheier T, Mayer R, Arzt W, Scheier M: Sonoembryology of the fetal posterior fossa at 11 + 3 to 13 + 6 gestational weeks on three-dimensional transvaginal ultrasound. Prenat Diagn 2016; 36: 731–737.
Altman DG: Construction of age-related reference centiles using absolute residuals. Stat Med 1993; 12: 917–924.
Altman DG, Chitty LS: Design and analysis of studies to derive charts of fetal size. Ultrasound Obstet Gynecol 1993; 3: 378–384.
Bland JM, Altman DG: Statistical methods for assessing agreement between two methods of clinical measurement. Lancet 1986; 1: 307–310.
Paladini D, Quarantelli M, Pastore G, Sorrentino M, Sglavo G, Nappi C: Abnormal or delayed development of the posterior membranous area of the brain: anatomy, ultrasound diagnosis, natural history and outcome of Blake’s pouch cyst in the fetus. Ultrasound Obstet Gynecol 2012; 39: 279–287.
Malinger G, Lev D, Lerman-Sagie T: The fetal cerebellum. Pitfalls in diagnosis and management. Prenat Diagn 2009; 29: 372–380.
Hochstetter F: Beiträge zur Entwicklungsgeschichte des Menschlichen Gehirns. Wien und Leipzig, Franz Deuticke, 1929.
Lachmann R, Sinkovskaya E, Abuhamad A: Posterior brain in fetuses with Dandy-Walker malformation with complete agenesis of the cerebellar vermis at 11–13 weeks: a pilot study. Prenat Diagn 2012; 32: 765–769.
Egle D, Strobl I, Weiskopf-Schwendinger V, Grubinger E, Kraxner F, Mutz-Dehbalaie IS, Strasak A, Scheier M: Appearance of the fetal posterior fossa at 11 + 3 to 13 + 6 gestational weeks on transabdominal ultrasound examination. Ultrasound Obstet Gynecol 2011; 38: 620–624.
Iuculano A, Zoppi MA, Piras A, Arras M, Monni G: Brain stem/brain stem occipital bone ratio and the four-line view in nuchal translucency images of fetuses with open spina bifida. J Matern Fetal Neonatal Med 2014: 1–4.
Volpe P, Contro E, Fanelli T, Muto B, Pilu G, Gentile M: Appearance of fetal posterior fossa at 11–14 weeks in fetuses with Dandy-Walker malformation or chromosomal anomalies. Ultrasound Obstet Gynecol 2016; 47: 720–725.
Bornstein E, Goncalves Rodriguez JL, Alvarez Pavon EC, Quiroga H, Or D, Divon MY: First-trimester sonographic findings associated with a Dandy-Walker malformation and inferior vermian hypoplasia. J Ultrasound Med 2013; 32: 1863–1868.
Copyright / Drug Dosage / Disclaimer
Copyright: All rights reserved. No part of this publication may be translated into other languages, reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying, recording, microcopying, or by any information storage and retrieval system, without permission in writing from the publisher.
Drug Dosage: The authors and the publisher have exerted every effort to ensure that drug selection and dosage set forth in this text are in accord with current recommendations and practice at the time of publication. However, in view of ongoing research, changes in government regulations, and the constant flow of information relating to drug therapy and drug reactions, the reader is urged to check the package insert for each drug for any changes in indications and dosage and for added warnings and precautions. This is particularly important when the recommended agent is a new and/or infrequently employed drug.
Disclaimer: The statements, opinions and data contained in this publication are solely those of the individual authors and contributors and not of the publishers and the editor(s). The appearance of advertisements or/and product references in the publication is not a warranty, endorsement, or approval of the products or services advertised or of their effectiveness, quality or safety. The publisher and the editor(s) disclaim responsibility for any injury to persons or property resulting from any ideas, methods, instructions or products referred to in the content or advertisements.
You do not currently have access to this content.