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.
What is the usual treatment and what is the prognosis?
Surgical resection is in most cases curative (>90% 5year survival).
Redemonstration of a large partially cystic mass, with its epicentre in the right cerebellar hemisphere, displacing and effacing the fourth ventricle, resulting in hydrocephalus.
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.