BACKGROUND: The detection of absent septi pellucidi (ASP) during obstetric ultrasound is a rare event. However, the clinical implications of this finding are significant. ASP can be associated with severe central nervous system anomalies such as holoprosencephaly, agenesis/dysgenesis of the corpus callosum, schizencephaly, severe ventriculomegaly, and open neural tube defects. In such cases, the prognosis is poor. When no such anomalies are identified, isolated ASP usually carries a good prognosis. However, some fetuses thought to have isolated ASP actually have septo-optic dysplasia (SOD), which is associated with optic nerve hypoplasia, hypothalamic-pituitary dysfunction, and developmental delay.
METHODS: A case in which fetal 3.0 Tesla magnetic resonance imaging (MRI) was considered crucial to definitively diagnose isolated ASP is presented. A review of the literature was conducted and analyzed to determine the role of MRI in the evaluation of fetuses with ASP, with special consideration on the differential diagnosis between isolated ASP and SOD.
CONCLUSIONS: Differentiating isolated ASP from SOD is imperative for adequate prenatal counseling. Unfortunately, making a prenatal diagnosis of SOD requires visualization and evaluation of the fetal optic nerves, chiasm, and pituitary gland, which is very demanding and not always possible using ultrasound. Fetal MRI has the potential of obtaining high-quality images of the fetal brain, and therefore this technique can be used for establishing the differential diagnosis in utero.

Septum pellucidum is a thin midline membrane that separates the anterior horns of the lateral ventricle. Agenesis of septum pellucidum (ASP) is considered a continuum of forebrain maldevelopment. Isolated ASP is a rare radiographic finding of unclear significance. We report a case of a 42-year-old male with ASP who presented with a new-onset seizure and eye closure sensitivity seen in the electroencephalogram. Magnetic resonance imaging of the brain confirmed the ASP. In the absence of data about the association between seizure and ASP, further studies are needed to determine its significance.

The absence of septum pellucidum (ASP) is a rare disease, which affects the structure of the brain. It is either isolated or associated with various congenital brain malformations. The diagnosis of ASP can be performed by second-trimester ultrasound. When the ASP is isolated, prenatal counseling is optimistic regarding neurological outcome, but there is a 20% risk of septo-optic dysplasia in the neonate.

Developmental malformations of the cortex in neuronal migration disorders result in constellation of findings on radiological scanning. Isolated defects are common but sometimes they occur in varying degrees of combination giving a unique appearance on the imaging studies. We describe a case of neuronal migration disorder in which the computed tomography scan showed the presence of lissencephaly, colpocephaly. and Septal agenesis. These findings make the ventricular system appear in shape of a crown, which we refer to as \"CROWN SIGN\", first described in neurosurgical literature..