·Spina bifida- Spina bifida may occur at any location along the spine but is most common in the lumbosacral region. Spina bifida is diagnosed when the posterior ossification centers splay outwardly and are further apart than the ossification centers above or below the defect. The cleft in the soft tissues is usually easily identified when the sac is intact and bulges into the amniotic cavity but findings can be minimal or absent. Spina bifida accounts for approximately 30% of all cases of ventriculomegaly. Sonographic examination of the head may demonstrate the ‘lemon’ and ‘banana’ signs. The ‘banana’ sign is related to the cerebellum when it is curved around the midbrain to produce a banana shaped structure. The lemon is the abnormal cranial shape. Associated anomalies involving other organs are common with spina bifida.
·Dany-Walker malformation- This syndrome is usually the result of abnormal development of the cerebellum and fourth ventricle. The fourth ventricle is seen as an enlarged cystic structure in the posterior fossa with splaying of the cerebellar hemispheres. The cerebellar vermis usually shows hypoplasia. Hydrocephalus is seen in up to 70% of fetuses. Associated anomalies involving other organs are fairly common. Prognosis depends on associated chromosomal anomalies and other organ defects.
·Artifact- Apparent ventriculomegaly may be recorded if an oblique view is inadvertently used to image the ventricle