Transabdominal sonography of the cavum septum pellucidum in normal fetuses in the second and third trimesters of pregnancy.
OBJECTIVES: To assess the visualization rate and size of the cavum septum pellucidum (CSP) by transabdominal sonography in normal fetuses throughout pregnancy. METHODS: The CSP was prospectively researched and measured using an axial transventricular plane in 286 consecutive uncomplicated singleton pregnancies between 15 and 41 weeks of gestation. RESULTS: The CSP was seen in 40% of cases at 15 weeks, 82% at 16-17 weeks, 100% at 18-37 weeks and 79% at 38-41 weeks. Compared to biparietal diameter (BPD), the visualization rate was 33% between 31 and 32 mm, 45% between 33 and 34 mm, 84% between 35 and 43 mm, 100% between 44 and 88 mm and 86% between 89 and 99 mm. Mean CSP width was 5.3 +/- 1.7 mm (range 2-9 mm). The CSP width increased with gestational age and BPD but with a slight decrease around term. CONCLUSIONS: In normal fetuses the CSP should always be visualized between 18 and 37 weeks, or with a BPD of 44-88 mm. Failure to observe the CSP in this interval, or possibly the presence of a large CSP, may indicate abnormal cerebral development and warrant further investigation. Conversely, absence of the CSP prior to 18 weeks, or later than 37 weeks, is a normal finding.