Abnormal septum pellucidum morphology Abnormal fetal central nervous system morphology Absent cavum septum pellucidum 2023-01-18T19:01:30Z The cavum septum pellucidum (CSP) is an important fetal midline forebrain landmark that is normally visible by prenatal sonography. This term refers to the lack of visibility of the CSP on prenatal sonography. The CSP normally can be visualized between 18 and 37 weeks of gestation. Lack of visualization of the CSP in this time period generally requires follow up and may indicate the presence of underlying malformations such as malformations of the corpus callosum. The lack of CSP before 18 weeks or after 37 weeks of gestation (or postnatally) is considered a normal finding.