Progressive multifocal leukoencephalopathy (PML) is a demyelinating disease which results from the JC virus infecting oligodendrocytes. It is considered the most common clinical manifestation of JC virus infection in the brain. Patients with PML present with various neurological symptoms. It typically spares the optic nerve and the spinal cord. Read more: http://radiopaedia.org/articles/progressive-multifocal-leukoencephalopathy
Melanoma is the third most common primary neoplasm that metastasizes to the brain. MRI T1: typically hyperintense secondary to hemorrhage or melanin (as above) T2: typically hypointense T1 C+ (Gd): typically enhances in a peripheral rim pattern or a diffusely heterogeneous pattern. http://radiopaedia.org/articles/intracranial-metastatic-melanoma-2
Acoustic schwannoma: most common cerebellopontine angle tumour.The most common presenting symptoms include; sensorineural hearing loss, tinnitus and vertigo. Contrast enhaced MRI is the investigation of choice for such lesions.