Bilateral subependymal pseudocysts as a pitfall in diagnosis of absence of the cavum septum pellucidum

Absent cavum septum pellucidum in the fetus is a common condition that may be associated with a variety of associated abnormalities. Herein, we present a case to emphasize a new pitfall in the differential diagnosis of the absence of the cavum septum pellucidum (CSP). Prenatal ultrasound views were concerning for partially absent CSP in the third trimester and subependymal pseudocysts (SEC) after a normal CSP visualization in the second trimester. The postnatal MRI demonstrated a normal corpus callosum, normal gyration, normal opthalmic nerves, and isolated SEC blocking the views of cavum septum pellucidum.