Interhemispheric cyst

Findings

There is agenesis of the corpus callosum. There is a multiseptated, left parasagittal midline cyst. Possible communication with the third ventricle. No associated enhancement is present. The left lateral ventricle appears dilated. No midline shift is present.

Differential diagnosis:
- Interhemispheric cyst
- Holoprosencephaly


Diagnosis: Interhemispheric cyst
At surgery: No definite communication with the ventricular system was found at surgery, thus categorizing the lesion as an interhemispheric cyst – type 2.


Key points


The association between an interhemispheric cyst and agenesis of the corpus callosum has been reported, although the etiology of the cyst is uncertain (arachnoid cyst, neuroepithelial cyst, or extensions of the ventricular lining).
Classification was most recently described by Barkovich et al based on appearance and communication with the ventricular system in 25 patients. Type 1 cysts communicate with the ventricular system while Type 2 cysts do not. Lack of communication with the ventricles was determined by visualizing a wall of the loculated cyst on MRI.

Classification of agenesis of the corpus callosum with interhemispheric cyst:
- Type 1a:
Cyst: Isointense to CSF (MR), unilocular.
Communication with lateral ventricles only.
Macrocephaly, hydrocephalus, Dandy-Walker malformation.
Males.

- Type 1b:
Cyst: Isointense to CSF (MR), unilocular.
Communication with and obstruction of third ventricle.
Macrocephaly, thalamic fusion without subcortical heterotopia.
Males > Females.

- Type 1c:
Cyst: Isointense to CSF (MR), unilocular.
Communication with lateral and third ventricles.
Microcephaly, cerebral dysplasia or hypoplasia.
Males.

- Type 2a:
Cyst: Isointense to CSF (MR), multilocular.
No communication with lateral or third ventricles.
Macrocephaly, hydrocephalus.
Male.

- Type 2b:
Cyst: Hyper attenuation (CT), hyper intense (T1W MR), multilocular.
No communication with lateral or third ventricles.
Aicardi syndrome, subependymal heterotopia, polymicrogyria, seizures, hypoplastic falx cerebri, uni- or bilateral ventriculomegaly, developmental delay.
Female.

- Type 2c:
Cyst: Isointense to CSF (MR), multilocular.
No communication with lateral or third ventricles.
Subcortical heterotopia, developmental delay.
Male.