Fetal ventriculomegaly (differential)

Fetal ventriculomegaly (ventricle width >10 mm) is an important finding in itself and it is also associated with other central nervous system abnormalities. For more information, see the main article fetal ventriculomegaly.

Differential diagnosis

Fetal ventriculomegaly can be thought of in terms of three categories:

• obstructive
• dysgenesis
• destructive

Obstructive causes

This category encompasses enlargement of a structurally normal cerebral ventricle.

• ventricles are typically smooth-walled
• ventricle orientation is normal
• cortex is intact, but compressed
• the posterior fossa structures may be abnormal
  • if normal, consider aqueductal stenosis
• the cavum septum pellucidi may be absent in severe obstructive ventriculomegaly
• the falx is present

One should search for an obstructing lesion causing the hydrocephalus.

Differentials include:

• Chiari II malformation
  • open lumbosacral myelomeningocele
  • small posterior fossa with inferiorly displaced cerebellum: banana sign
  • angulation of frontal bones: lemon sign
• Dandy-Walker spectrum
  • diagnosed >18 weeks (after vermis development ends)
  • cystic dilatation of the fourth ventricle
  • cerebellar vermis agenesis
  • upward displacement of the torcula
• aqueductal stenosis
• obstructing masses

Dysgenesis causes

This category encompasses enlargement of a structurally abnormal cerebral ventricle:

• ventricle shape and position is abnormal
• ventricles are typically smooth-walled
• the cavum septum pellucidi is abnormal
• falx is often normal
• the cerebral cortex is intact (with the exception of open lip schizencephaly)
• other CNS abnormalities may be visible (e.g. fused frontal horns)

Differentials include:

• agenesis of the corpus callosum
  • may not be apparent until >22 weeks
• septo-optic dysplasia
• holoprosencephaly
• schizencephaly

Destructive causes

This category encompasses vascular events (infarcts) to the developing brain.

• ventricle position is normal
• the ventricle wall may be nodular from old hemorrhage
  • ventricular walls are smooth with periventricular leukomalacia
• thinning/loss of cerebral cortex in a patchy asymmetric distribution
• midline structures are normal
• posterior fossa structures are normal
• the falx is present

Differentials include:

• intracranial hemorrhage
• hydranencephaly: complete destruction of cerebral cortex
  • important to differentiate this from severe hydrocephalus, which maintains a very thin cortical rim
• periventricular leukomalacia
  • can be seen before birth
  • increased periventricular echogenicity
• infection, e.g. cytomegalovirus