Absent Septum Pellucidum

A six-week-old infant was referred to the paediatric neurology unit of a tertiary care hospital in 2019 from a peripheral hospital for further evaluation. This referral was prompted by an antenatal scan that revealed an absent cavum septum pellucidum and a postnatal head ultrasound that suggested septo-optic dysplasia. Despite these findings, the infant appeared to be developing normally with normal muscle tone, strength and sucking reflex. The infant was born at full term via spontaneous vaginal delivery with a birth weight of 3 kg, head circumference of 34 cm, length of 52 cm and a good Apgar score; he had also received all vaccinations recommended at birth. There was no history of maternal infection during pregnancy, medication intake, smoking or substance abuse. His parents were consanguineous, but there was no family history of genetic or neurological disorders.

An ophthalmologist examined the patient and found no optic nerve atrophy or other ocular abnormalities. Magnetic resonance imaging (MRI) of the brain at the age of 33 months revealed an isolated absence of the septum pellucidum (ASP) but no signs of septo-optic dysplasia, optic nerve hypoplasia or visible pituitary abnormalities [Figure 1]. Furthermore, an endocrinological evaluation revealed no endocrine abnormalities. The patient, who was 3 years old at presentation, was healthy with no obvious physical abnormalities and showed age-appropriate development; thus, he was diagnosed with isolated ASP.

Figure 1.

A: Magnetic resonance imaging of the brain of the patient at 33 months of age showing absence of the septum pellucidum in an axial T2-weighted image. B: Coronal T2-weighted image showing squaring of the frontal horns with inferior pointing (arrowheads). The pre-chiasmatic segments of the optic nerves are bilaterally visible with normal size (arrows). C: An axial T2-weighted image from another patient showing normal septum pellucidum (yellow arrow).

Informed consent was obtained from the parents for the publication of the images.

Comment

ASP is a rare developmental brain anomaly that can be partial or complete. It is often associated with congenital brain defects, such as holoprosencephaly, septo-optic dysplasia, schizencephaly and corpus callosum agenesis. Isolated ASP should be suspected in infants with normal findings on neurological examination but with an absent cavum septum pellucidum on antenatal scans.1 It is challenging to differentiate between isolated ASP and septo-optic dysplasia in utero using current imaging techniques because it can be difficult to rule out the possibility of optic nerve hypoplasia and endocrine abnormalities.2 Prenatal ultrasonography can detect cavum septum pellucidum between 18 and 37 weeks of gestation, or with a biparietal diameter of 44–88 mm. The mean width of the cavum septum pellucidum is 5.3 ± 1.7 mm with a range of 2 to 9 mm.3 If the cavum septum pellucidum is not detected on antenatal scanning during this period, it may indicate abnormal brain development and necessitate further examination.4

Isolated ASP is uncommon, occurring in approximately 0.2–0.3 of every 10,000 people. However, the true incidence might be higher due to limitations in sonography such as skills of the operator, restricted field of view and visualisation.5 The prognosis of this condition is presently unknown, but it has been associated with undetectable pathological changes on ultrasound or MRI.4

Few cases of isolated septal agenesis have been associated with schizophrenia as it is considered part of the limbic system.4 Other cases have been associated with speech delays or behavioural problems.4 In a retrospective cohort study, antenatal genetic tests were performed in 30 fetuses with suspected isolated ASP, two of which had an abnormal result.6 The majority of cases with a prenatal isolated ASP diagnosis have a favourable prognosis.6 However, if other anomalies are detected, the clinical outcome is worse.6 Screening for associated anomalies is mandatory for newborns who are identified with ASP on antenatal ultrasound. An early understanding of whether ASP is an isolated anomaly or part of a syndrome enables clinicians to provide appropriate counselling for families and to establish early rehabilitation and guidance for future management of such patients.