History of interhemispheric cyst seen on ultrasound. 19 weeks gestational age. Large field-of-view images demonstrate mild maternal right hydroureteronephrosis, not unexpected in pregnancy.Small field-of-view images of the fetal brain demonstrate that the fetal ventricles are normal in size. There is a normal cavum septum pellucidum and possible small cavum vergae. There is prominence of the CSF space posterior to the cavum septum pellucidum situated between the hemispheres and superior to the tectum which could represent a normal variant prominent cistern or a cyst of the cavum vellum interpositum.The degree of cortical development appears within normal limits for age. No focal parenchymal abnormalities are identified. The corpus callosum and cerebellum appear appropriately formed.
Prominent CSF space posterior to the cavum septum pellucidum which could represent a normal variant prominent cistern or cyst of the cavum vellum interpositum. Sonographic follow-up and/or dedicated postnatal imaging can be considered as clinically warranted.