Dandy Walker malformation

Bilateral severe ventriculomegaly is noted with the right lateral ventricle measuring 23mm and the left lateral ventricle measuring 14 mm.

The posterior fossa is abnormal. The cisterna magna is grossly enlarged with the cerebellum severely compressed. The vermis is not clearly visualized. The CSP and corpus callosum appeared present but compressed. 

The remainder of the fetal anatomy, including the face, spine, heart, abdomen and limbs was normal.

Selected images from the follow-up fetal MRI study performed at 22w 3d.

Ventricles and CSF spaces: Gross dilatation of the lateral ventricles is noted with a colpocephalic pattern, with the ventricular enlargement affecting the trigones more than the frontal horns. The third ventricle by comparison does not appear dilated. The extra-axial CSF spaces particularly overlying the parietal and occipital lobes are narrowed due to the gross dilatation ventricular system.

Hemispheres: There is thinning of the hemispheric parenchyma. There is no evidence of formation of the Sylvian, parieto-occipital or calcarine fissures . In addition, there is focal cortical malformation affecting the left and right frontoparietal lobes (see key images) where there is overfolding of the cortex. Elsewhere, the hemispheric parenchyma appears thinned as a result of underlying ventricular enlargement, but the hemispheres are otherwise unremarkable.

Septum pellucidum: The 2 leaves of the septum pellucidum are seen anteriorly but not posteriorly. Whether this is due to perforation of the septum pellucidum as a consequence of severe ventriculomegaly or primary lack of complete formation is uncertain. In addition, there is evidence of perforation of the dilated right lateral ventricle through the right parieto-occipital parenchyma. This is also a commonly recognized consequence of severe ventriculomegaly in the fetus.

Corpus callosum: This is difficult to identify on the sagittal images as is often the case when the ventricles are as dilated as they are here. The configuration the lateral ventricles on the coronal images does not suggest complete absence of the corpus callosum although the corpus callosum does appear to be very thin and again this could be a reflection of the ventricular dilatation rather than a primary abnormality of the corpus callosum. These possibilities cannot be distinguished.

Cerebellum: Vermis foliation absent. A tiny amount of cerebellar tissue is seen in the expected position of the superior vermis in the midline. Tegmentovermian angle not measurable. Hemispheres present but abnormally small. Retrocerebellar CSF space the posterior fossa is grossly enlarged and the torcular is elevated above the level of the cervical musculature insertion confirming posterior fossa enlargement.

Brainstem: The pons appears mildly thinned but the expected pontine convexity is present and the relative sizes of the pons, midbrain, and medulla are normal.

Remainded of the fetal anatomy appeared normal.

MRI courtesy of A/Prof Stacy Goergen