Differential diagnosis of term brain cysts

• Arachnoid cyst
• Agenesis of the corpus callosum with interhemispheric cyst
• Cavum septum pellucidum
• Cavum vellum interpositium
• Cavum vergae
• Encephalocoele

Approach to the differential diagnosis of term infant brain cysts:

• Arachnoid cyst – cyst is extraaxial in location, of varying size, can be anywhere in the brain, may cause bone erosion
• Agenesis of the corpus callosum with interhemispheric cyst – large midline cyst actually is a high riding third ventricle
• Cavum septum pellucidum – cyst lies between the leaflets of septum pellucidum
• Cavum vellum interpositium – cyst lies between the atria/trigones of the lateral ventricles
• Cavum vergae – cyst is posterior extension of cavum septum pellucidum and anterior to the splenium of the corpus callosum
• Encephalocoele – intracranial cyst communicates with extracranial cystic structure