Findings:
Bilateral infratentorial, retro-cerebellar arachnoid cysts, compressing the cerebellar hemispheres and elevating the tentorium with associated remodelling of the adjacent skull vault.
There is no hydrocephalus or midline shift.
The third ventricle is parallel to the lateral ventricles due to complete agenesis of the corpus callosum. Consequential racing car appearance of the lateral ventricles.
Mild herniation of the right temporal mesial structures into the right ambient cistern.
The brain parenchyma is unremarkable. No abnormal signal on the susceptibility weighted images or diffusion/ADC images is identified.
No heterotopia, no hippocampal pathology.
The pituitary gland is normal.
Mucosal thickening is seen within the frontal and ethmoid sinuses bilaterally. The paranasal sinuses and the mastoid air cells are otherwise clear. No bony abnormality is seen.
Conclusion:
Complete agenesis of the corpus callosum.
Retro-cerebellar arachnoid cyst.