Which three tumours should you consider?
Subependymoma, central neurocytoma and ependymoma.
Which would you favour? Why?
Subependymoma is most likely in a patient of this age and given the lack of significant enhancement. It is also completely intraventricular, whereas ependymomas tend to have a parenchymal component.
On T2 weighted images the mass (red arrow) is almost the same signal intensity as CSF and you could be excused for at least thinking that it could be flow related artefact. On FLAIR the mass is clearly not CSF as is much more easily seen (yellow dotted line).