To evaluate the value of prenatal ultrasound and magnetic resonance imaging (MRI) in the diagnosis of fetal cavum septum pellucidum (CSP) abnormalities and to analyze the pregnancy outcomes.

From January 2018 to December 2019, 34 fetuses with CSP abnormalities identified by prenatal ultrasound at the Shenzhen Maternity and Child Healthcare Hospital, the First School of Clinical Medicine, Southern Medical University were collected. Fetal MRI was performed. the newborn or fetus was examined after birth or induced labor by ultrasound and MRI. Neurodevelopment was followed by postnatal ultrasound/MRI.

Prenatal ultrasound and MRI examination results showed that in the 34 cases, there were 7 cases of holoprosencephaly (20.6%), 9 cases of small CSP (26.5%), 3 cases of absent CSP (8.8%), 7 cases of widened CSP (20.6%), 4 cases of corpus callosum dysplasia (11.8%), 1 case of abnormal echo in CSP (2.9%), 1 case of isolated septum pellucidum dysplasia (2.9%), and 2 cases of septo-optic dysplasia (5.9%). There were 24 fetuses (70.6%) who underwent fetal MRI, which revealed 11 cases of small CSP (45.8%), 5 cases of widened CSP (20.8%), 4 cases of corpus callosum dysplasia (16.7%), 2 cases of isolated septum pellucidum dysplasia (8.3%), and 2 cases of septo-optic dysplasia (8.3%). In four cases, prenatal ultrasound and prenatal MRI diagnoses were inconsistent. Fifteen cases (44.1%, 15/34) underwent induced labor (7 cases of holoprosencephaly and 8 cases of abnormal CSP with other malformations). Nineteen cases (55.9%, 19/34) were born and developed well (11 cases with small CSP, 5 cases with widened CSP, 1 case with corpus callosum dysplasia, and 2 cases with isolated septum pellucidum dysplasia and normal corpus callosum). No neurological abnormalities were observed in 19 live births between 1 month and 28 months.

Isolated small or wide CSP and isolated septum pellucidum dysplasia have good clinical prognosis during short-term follow-up.