Classification of agenesis of the corpus callosum with interhemispheric cyst after Barkovich et al (3)

Type 1*
Subtype	Cyst Characteristics	Communication	Associated Abnormalities
Type 1a: Presumed communicating hydrocephalus	Isointense to CSF (MR), unilocular	Communication with lateral ventricles only	Macrocephaly, hydrocephalus, Dandy-Walker malformation
Type 1b: Hydrocephalus secondary to diencephalic anomaly	Isointense to CSF (MR), unilocular	Communication with and obstruction of third ventricle	Macrocephaly, diencephalic malformation (eg, thalamic fusion without subcortical heterotopia)
Type 1c: Small head size and cerebral hypoplasia	Isointense to CSF (MR), unilocular	Communication with lateral and third ventricles	Microcephaly, cerebral dysplasia or hypoplasia
Type 2†
Type 2a: No abnormality apart from ACC	Isointense to CSF (MR), multilocular	No communication with lateral or third ventricles	Macrocephaly, hydrocephalus
Type 2b: Aicardi syndrome	Hyperattenuation (CT), hyperintense (T1W MR), multilocular	No communication with lateral or third ventricles	Female predominance, subependymal heterotopia, polymicrogyria, seizures, hypoplastic falx cerebri, uni- or bilateral ventriculomegaly, developmental delay
Type 2c: Subcortical heterotopia	Isointense to CSF (MR), multilocular	No communication with lateral or third ventricles	Subcortical heterotopia, developmental delay

^*Extension or diverticulation of third or lateral ventricles.

^†Loculated, lack of communication with ventricular system.