Well defined altered signal intensity lesion noted in right cerebellar hemisphere along the tentorium. This is seen to cross the midline. Anteriorly, this is seen to compress the vermis and fourth ventricle, causing upstream dilatation of the ventricular system. Posteriorly, this is seen to cause mass effect over the medulla with inferior displacement of cerebellar tonsil. Posterosuperiorly, this is seen to abut the right transverse sinus. Diffusion restriction noted. Post-contrast study shows homogenous enhancement of the lesion.
Obstructive hydrocephalus with transependymal CSF spread noted around the lateral ventricle.
Ascending transtentorial herniation noted on right side. Effacement of adjacent basal cisterns noted.
Prominent CSF signal noted around the optic nerves bilaterally.
Possibilities of medulloblastoma vs pilocytic astrocytoma are considered.