Volume Measurement of the Cavum Septi Pellucidi: Normative Values Between 20 and 40 Weeks of Gestation

Background: The cavum septi pellucidi (CSP) is a brain -enclosed cavity located on the midline between the two leaflets of the septum pellucidum that separates the lateral ventricles. This structure develops in the fetus from week 18 and can be seen up to week 37 in almost all cases and then begins to disappear. Objectives: To measure and determine the normative values of the CSP volume in fetuses between 20 to 40 weeks of gestation. Methods: The study comprised 161 consecutive pregnant women between 20 to 40 weeks of gestation with single viable fetuses. All patients had normal, disease -free pregnancies. Transvaginal or transabdominal ultrasound was used according to the fetal presentation. The fetal head was assessed in mid-sagittal sections. Once the CSP was visualized, its volume was measured using three-dimensional ultrasound with Virtual Organ Computer -aided Analysis software. The width of the CSP was also measured at the biparietal diameter (BPD) plane. Results: Of the 161 fetuses, the CSP volume was measured in 158. In three patients the CSP was not identified. The CSP volume correlated poorly with gestational age (r=0.229) and with the BPD (r=0.295). The mean CSP volume was 0.508 +/- 0.372 ml (range: 0.03-1.78 ml). The simple measurement of the CSP width correlated better with gestational age (r=0.535) and the BPD (r=0.484). Conclusions: The CSP volume had a poor correlation with gestational age; however, the volume did not exceed 2 ml regardless of gestational age. This information can be used to assess pathologies involving the CSP.