Exploring the fetal brain: imaging, prognosis and counselling

There is marked biologic variability in the size of the fetal lateral ventricles. Empiric data suggests that fetuses with a width of the atrium (or posterior horn) of lateral ventricles of 10 mm or more have an increased risk of abnormal outcome. When the measurement is 10-15mm the risk is relatively low.

The current definition is an increased size of the lateral ventricles, with a transverse diameter of the atrium in excess of 15mm without evidence of other cerebral malformations. It is a rare condition, usually a part of complex cerebral abnormalities, less frequently the consequence of obstructed cerebrospinal fluid turnover.

Intracranial hemorrage may occur within the lateral ventricles or in the subdural space. The sonographic appearance changes with time. An echogenic collection is first seen, and in the following days it develops into a complex mass frequently complicated by sever ventriculomegaly.

Porencephaly is characterized by single or multiple cysts replacing the brain parenchyma. The cyst may communicate with the lateral ventricle, subarachnoid space or both. It is usually a sporadic condition caused by hemorrage, ischemia or infections.

Aqueductal stenosis (AS) results from a narrowing or occlusion of the aqueduct of Sylvius.

Holoprosencephaly derives from failure of separation of the cerebral hemispheres. In the most severe forms there is one undivided cerebral mass that contains a crescent shaped rudimentary ventricular cavity. In these cases, severe cranio-facial anomalies (cyclopia, hypotelorism, median cleft face) are associated.

Under this term are included a group of conditions that share in common one sonographic findings: the impression that the fourth ventricle communicates with the cisterna magna. These conditions include: Dandy-Walker malformation, Blake’s pouch cyst, vermian hypoplasia/agenesis. They have a similar sonographic appearance, particularly in early gestation, and differentiation requires a multiplanar approach.

Enlarged (> 10 mm) cisterma magna with a normal cerebellum. It may be associated with other anomalies, including trisomy 18 and other cerebral malformations. When isolated, fetal mega cisterna magna has a good chance of intrauterine remission, and is usually (> 90%of cases) associated with a good outcome.

Malformations of cortical development (MCDs) are neurodevelopmental disorders that result from abnormal development of the cerebral cortex in utero secondary to genetic, infectious or vascular causes.

It is the consequence of two types of arteriovenous malformation: the vein of Galen aneurysmal malformation and the pial arteriovenous malformation. The sonographic appearance is similar and the most prominent finding is the enlargement of the vein of Galen, that on Color Doppler contains turbulent blood flow.

Thrombosis of the dural sinus occurs rarely in intrauterine life. It is characterized by the dilatation of the most inferior and posterior portion of the superior sagittal sinus and of the sinus confluence, that appear as a fluid collection in the occipital area of the fetal cranium.

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