Does the MRI change you most likely diagnosis?
It shouldn't. Pilocytic astrocytoma is still the most likely diagnosis, and more typical enhancement is demonstrated.
MRI of the brain confirms the findings on CT. A large partially cystic mass has its epicentre in the right cerebellar hemisphere, displacing and effacing the fourth ventricle, resulting in hydrocephalus (these ventricles are far too large for an 8 year old child).
The mass has a solid component, which is nodular, and slightly hypointense on T1 compared to the cerebellum, and hyperintense on T2. It demonstrates bright contrast enhancement.