Severe bilateral lateral ventriculomegaly but the third ventricle is non dilated. The septum pellucidum is absent, with configuration of the frontal horns suggesting that this is likely due to perforation of the septal leaves rather than failed formation. Supporting this is:
- The severe degree of ventriculomegaly
- Severe thinning of the parenchyma overlying the occipital horns of the lateral ventricles consistent with increased intraventricular pressure.
Impression of a forniceal nodule suggesting the fornices are fused and that the absence of the septal leaves is therefore malformative rather than destructive. However, this appearance can be due to close approximation of two separate fornices due to limited spatial resolution of fetal MRI.
The corpus callosum is present but very thin.
The Sylvian fissures are very shallow and other sulci that should be seen at 22 weeks, namely the parieto-occipital and calcarine sulci, are not evident. This can occur when ventriculomegaly is present, especially when it is severe, due to stretching and effacement of the sulci rather than primary failure of formation.
Although there is some evidence of lamination in the hemispheric parenchyma, it is difficult to assess for normality due to the parenchyma being stretched and thinned by the enlarged ventricles.
Normal brainstem and cerebellum. Note that the ganglionic eminences are not enlarged,
Although the aqueduct of Sylvius is difficult to identify on the sagittal images this can be the case on fetal imaging when motion degradation is present and is not necessarily specific for aqueductal obstruction.
In summary, the severe lateral ventricular dilatation combined with parenchymal thinning over the occipital horns of the lateral ventricles suggests an obstructive cause for the absent septal leaves due to perforation.