Guidelines for the Management of an Isolated Enlarged Cavum Septum Pellucidum: a Case Report

Case Diagnosis: Enlarged cavum septum pellucidum (CSP) on ultrasound with otherwise normal neuroanatomy.

Case Description or Program Description: We present the case of a patient, the son of one of the authors, identified on prenatal screening with an enlarged CSP. At 24 weeks and 4 days gestation, an anatomy scan showed the CSP at the 95th percentile (7.5 mm). Two weeks later, a maternal-fetal medicine consultation revealed further enlargement to 9 mm. The parents were advised that while this could be normal, it has been associated with aneuploidy and 22q deletion syndrome.

Setting: Inpatient hospital.

Assessment/Results: At over eleven months, the patient has met or exceeded pediatric developmental milestones, including gross motor, fine motor, language, and emotional skills.

Discussion (relevance): The CSP is a normal midline fetal brain structure, identifiable by 18 weeks and typically closing by 3-6 months postnatally. Its function remains unclear but has been hypothesized to serve as a neurodevelopmental marker, cerebrospinal fluid reservoir, or indicator of traumatic brain injury when persistent in adulthood. Developmental CSP abnormalities often involve its absence, signaling serious congenital brain defects. An isolated enlarged or persistent CSP postnatally has been linked to neurodevelopmental and psychiatric disorders such as schizophrenia, autism spectrum disorder, and ADHD, as well as chromosomal abnormalities like trisomy 13, 18, and 21.

Conclusions: Evidence-based counseling on CSP abnormalities in prenatal imaging is essential. Distinguishing isolated cases from those with additional abnormalities is critical. An isolated enlarged CSP is often benign, not necessarily indicative of chromosomal abnormalities. Instead, it may be a marker for mild neurodevelopmental delay, warranting follow-up with a pediatric specialist for further evaluation if needed. Parents should be reassured when no other abnormalities are present.