Your doctor will order a CT scan with contrast. The contrast is an IV that allows a better images of the thymus. If the images reveal a problem with the thymus, like a tumor or other abnormality, removal may be indicated.

A thymectomy is not a panacea, though. It may takes months or longer to see any lessening of symptoms after the surgery. Sometimes even if there was improvement in the months or years following the thymectomy, symptoms can return.

The MG manual has a section on the thymectomy procedure.

Myasthenia Gravis: A Manual for the Health Care Provider (PDF) - page 18

There are three different approaches to a thymectomy. See a recent thread on this topic:

http://neurotalk.psychcentral.com/thread202577.html

-Mark-