I was diagnosed after symptoms drove an investigation. It seems like you had some symptoms if you were looking into a pituitary adenoma. Did you have facial numbness or double vision? These are symptoms shared with pitutiary adenoma. It does happen but certainly it is more common that you have symptoms that eventually lead to MS.............not MS lesions on an MRI leading to a diagnosis.
First of all, you can have lesions without having MS. Lesions can be caused by migraines, Lyme Disease, venous abnormalities, infections etc. However, there can be a certain look to MS lesions.
If you are at all questioning the diagnoses, be sure to get your MRI on a disc and a copy of the report and then go for a second opinion. The best way seems to be by going to an MS specialist.
If you indeed have MS, then it seems you may have a rare early diagnosis. This means you can get on treatment early and hopefully it will slow down the progression of MS.
Please make sure you have your insurance in place with good prescription coverage before you allow MS to be added officially to your medical file. Check out this site for more information on the diagnostic process for MS. Good luck to you!