Sonographic appearance of the cavum septum pellucidum et vergae in normal fetuses in the second and third trimesters of pregnancy

Background To characterize the cavum septum pellucidum et vergae (CSPV) in normal fetuses in the second to third trimester. Methods The cavum septum pellucidum (CSP) and CSPV were investigated in 322 uncomplicated singleton pregnancies from 25 to 39 weeks' gestation. Visualization rate, width, and morphology of both CSP and cavum vergae (CV) were assessed by ultrasound and MRI. Results The CSP and CSPV visualization rates were 100% and 7.8% (25/322), respectively. The mean widths were 6.3 ± 1.2 mm (3.4–10 mm) and 6.7 ± 1.0 mm (5.1–9 mm), respectively, with no significant correlation between width and gestational age (r = −0.108, p > 0.05 and r = −0.182, p > 0.05, respectively). In CSPV fetuses, the CV to CSP ratio was 1.004 ± 0.018 (0.967–1.033). All CSPVs were rectangular in the transverse plane and extended posteriorly beyond the midpoint of the brain. Conclusions Common features of CSPVs include (1) a rectangular morphology, (2) communication between the two cavities, (3) a CV width within the normal range for CSP, and (4) a CV-CSP ratio of 1. These findings may help distinguish normal from abnormal CSPV. © 2013 Wiley Periodicals, Inc. J Clin Ultrasound 41:525–531, 2013.