C, I wouldn't put too much stock in PET, MRI or CT scans. My cancer never showed up on any of these scans. Erik hit it on the head - biopsy. My was tonsil cancer, it was visually identified and later confirmed with a biopsy.

In my non-medical opinion, if the small lump on the right side of your neck persists, that would be a candidate for a needle biopsy.