CNS Tumors — Specific Entities and Imaging

Which imaging finding is most characteristic of pilocytic astrocytoma on MRI?

A 35-year-old woman presents with progressive headaches and visual disturbances for 3 months. MRI brain with contrast shows a large sellar mass with suprasellar extension, homogeneous enhancement, and no cystic component. The mass compresses the optic chiasm from below. Serum prolactin is markedly elevated at 2500 ng/mL. What is the most likely diagnosis?

A 42-year-old man presents with progressive gait ataxia and headaches for 6 weeks. MRI brain shows a well-demarcated, round mass in the cerebellar hemisphere with homogeneous T2 hyperintensity, minimal surrounding edema, and marked enhancement after gadolinium. There is no cystic component. Cerebrospinal fluid analysis shows elevated protein. What is the most likely diagnosis?

A 7-year-old child presents with progressive ataxia, morning vomiting, and headaches. Imaging shows a midline posterior fossa mass with cystic and solid components, obstructing the fourth ventricle. Which investigation is most appropriate to confirm the diagnosis of medulloblastoma and assess for leptomeningeal spread?

A 35-year-old woman presents with progressive headaches and bitemporal hemianopsia. MRI brain shows a sellar mass with suprasellar extension. Which investigation is most specific for confirming the diagnosis of pituitary adenoma?