The differential diagnosis of severe ventriculomegaly with a kinked brainstem and vermian hypoplasia includes dystroglycanopathy, tubulinopathy and mutations in the L1CAM gene on the X-chromosome.

In this case, L1 CAM mutation was favored due to the following imaging features:

• presence of thumb adduction,
• absence of abnormal basal ganglia enlargement or cavitation, seen commonly in fetuses with various causes of lissencephaly including tubulinopathy and dystroglycanopathy, and
• absence of globe abnormalities (microphthalmia, buphthalmos, persistent hyperplastic primary vitreous and/or retinal detachment), which occur in some cases of dystroglycanopathy.

The patient also had a sister with an intellectually disabled son, suggesting a disorder with an X-linked mode of inheritance

Although there is some overlap in the imaging appearance of these conditions and genetic analysis is required, this case illustrates the utility and complementarity of US and MRI in guiding the diagnosis.