Ultrasound Obstet Gynecol 2013; 42: 156–160 Published online in Wiley Online Library (wileyonlinelibrary.com). DOI: 10.1002/uog.12393 The cavum septi pellucidi in euploid and aneuploid fetuses H. ABELE*, O. BABIY-PACHOMOW†, J. SONEK‡, M. HOOPMANN*, M. SCHAELIKE§ and K. O. KAGAN* *Department of Obstetrics and Gynaecology, University of Tuebingen, Tuebingen, Germany; †Department of Obstetrics and Gynaecology, Klinikum Bad Cannstatt, Stuttgart, Germany; ‡Fetal Medicine Foundation USA, Dayton, OH, USA and Division of Maternal Fetal Medicine, Wright State University, Dayton, OH, USA; §Center for Prenatal Diagnosis and Genetics, Nuremberg, Germany KEYWORDS: biparietal diameter; fetal head biometry; screening; second trimester; trisomy ABSTRACT Objective To examine whether the cavum septi pellucidi (CSP) is larger in second- and third-trimester fetuses with chromosomal abnormalities than in euploid fetuses. Methods This was a retrospective study utilizing stored two-dimensional images of second- and third-trimester fetuses between 18 and 40 weeks’ gestation from three centers in Germany. The width of the CSP was measured by placing the calipers on the inner portion of its lateral borders. Two operators, both of whom were blinded to the fetal karyotype and to the measurements obtained by the other, measured the CSP width. The normal range in euploid fetuses was computed based on the biparietal diameter (BPD) by applying univariate regression analysis. The CSP width in euploid and aneuploid fetuses was transformed into Z-scores and compared using Student’s t-test. Univariate regression analysis was used to determine the dependency of Z-score on head biometry. Results The study population consisted of 406 singleton pregnancies, 267 with euploid fetuses, 81 with trisomy 21, 50 with trisomy 18 and eight with trisomy 13. In the euploid group, the mean CSP width was 4.5 (range, 1.8–7.4) mm. Regression analysis showed a significant dependency of CSP width on BPD (CSP width = 0.658 + (0.064 × BPD), r = 0.781, P < 0.0001; both parameters in mm). The mean CSP width increased from 3.2 to 7.1 mm for BPD values of 40 to 100 mm, respectively. In the groups of fetuses with trisomy 21, 18 and 13, mean CSP width was 5.7 (range, 2.8–10.5), 7.9 (range, 3.5–12.8) and 5.8 (range, 4.0–9.0) mm, respectively. In 42.0% of the fetuses with trisomy 21, CSP width was above the 95 th centile. In trisomy 18 and 13, CSP width was above the 95 th centile in 92.0% and 37.5% of cases, respectively. Correspondence to: Prof. K. O. Kagan, University of Tuebingen, Calwerstrasse 7, 72076 Tuebingen, Germany (e-mail: [email protected]) Accepted: 31 December 2012 Conclusion A large CSP width should prompt a detailed ultrasound examination to further assess the risk for chromosomal abnormalities. Copyright 2013 ISUOG. Published by John Wiley & Sons Ltd. INTRODUCTION Even though first-trimester combined screening is cur- rently the most efficient method for detecting aneuploidy, screening in the second trimester continues to be impor- tant for two main reasons. First, not all aneuploidy is detected at the time of the first-trimester scan and a sub- sequent second-trimester evaluation can help to pick up additional cases; second, not all patients are seen early enough to undergo first-trimester screening. Prenatal screening for aneuploidy focuses mainly on the three common autosomal trisomies 21, 18 and 13. There are specific ultrasound findings that can be associated with each of these chromosomal abnormalities, many of which are located within the fetal head and face. In trisomy 21, there is often brachycephaly, mild ventriculomegaly, nuchal edema, increased prenasal skin thickness, a short or absent nasal bone and a decreased prefrontal space ratio. Trisomy 18 is often associated with a strawberry-shaped head, choroid plexus cysts, absent corpus callosum, posterior fossa abnormalities, a flat face, facial clefts and retrognathia. Trisomy 13 can be associated with holoprosencephaly, megacisterna magna, abnormal interocular distance (hypotelorism up to cyclopism) and midfacial clefts 1 – 3 . Little is known about the cavum septi pellucidi (CSP) in aneuploid fetuses, although it is an easily identifiable structure on prenatal ultrasound. In the transverse plane of the fetal head, it is seen as a hypoechoic, roughly rectangular structure, located in the midline and anteriorly to the third ventricle. It becomes visible by about 18 weeks’ gestation and is an important landmark during an Copyright 2013 ISUOG. Published by John Wiley & Sons Ltd. ORIGINAL PAPER
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