Stage IIa to Brain Mets?

I was diagnosed stage IIA last June (3 cm tumour, 6 negative nodes, er- pr+, her2+++)and just finished treatment last month and am waiting to find out my status regarding the HERA trial (yes. still!). MEANWHILE, I started getting headaches about 6 weeks ago along with a sort of fuzzy, heavy feeling in my head. Anyway. I finally got my onc. to agree to a scan (CT with contrasting dye) which I had last week. Last night he phoned to say that there is a "nodule" in the right lateral ventricle. He didn't give many details (and it was my husband who actually took the call -- I would rather hear bad news from him) but said they're "pretty sure" its not cancer but they want to now do an MRI to get a better look...
I don't believe they can rule out cancer based on a CT image, but just wonder if anyone knows what else this might be if not cancer? I see the onc. tomorrow morning and will get more details...

Any info/shared experiences would be great.

/Christine