Donnab, if it pushes you to Addison's, it would be primary. From a JAMA page, "Primary AI is relatively rare but develops in patients who have greater than 90% destruction or replacement of the adrenal glands with inflammation, tumor, infection, or hemorrhage." There is also secondary and tertiary, which deal with ACTH and HPA axis dysfunction, respectively.
This healthboard and reputable medical websites are a Godsend for information on this. Imagine 15 years ago when you had to find a knowlegable, reputable and skillful doctor, just the right book.
Hoping the surgery goes perfectly for you. No surgery is minor or routine if it is yours!