will a brain mri show a posterior fossa brain tumor

would a mri of the brain show a posterior fossa brain tumor? I had a brain MRI and results were normal. I had a cervical spine mri and it showed vermian atrophy and increased extra-axial fluid in the posterior fossa. Does this mean there is a tumor present or could the fluid be from other causes. I also have pain in the back of the neck that could indicate nerve involvement due to a tumor. I am scheduled to see a Neurologist in about ten days. but am quite anxious about the findings on the MRI report