Although the cavum septi pellucidum and the cavum Vergae are ultrasonically discernible intracranial structures of the fetus,
their developmental process and abnormalities have remained obscure until this time. The first published study of abnormal
dilatation of the cavum Vergae has recently appeared, however. Here we report on a case of what appeared to be dilated cavum
septi pellucidum and cavum Vergae with uneventful pre- and postnatal periods, as well as on the results of a study of these two
cavities in a normal population of fetus in their second and third trimesters of pregnancy. The cavum septi pellucidum and
cavum Vergae were visualized during each week from the 18th through the 40th week of pregnancy at a constant mean rate of
75%. The width of both cava in transverse and coronal sections increased almost linearly from 4 mm in the 18th week of
pregnancy to 10 mm in the 40th week. We thus conclude that the cavum septi pellucidum and cavum Vergae are fetal
intracranial structures normally detected on ultrasound examination during the second and third trimesters of pregnancy.
Clarification of the clinical significance of their dilatation may require further investigation, however.