The only thing I can think of is to take the CD of the scan to another radiologist for a second 'reading' and report. I would let them know ahead of time that you want ALL findings reported...specifically the anatomical variations.

Keep in mind though, your insurance will be billed for the reading and you'll incur any copay. This is probably why he won't change the original report...because he won't get paid to do so. It's all about money in the end.