I had a rather interesting experience. My craniotomy was not for an AN, but another tumor. I was in the midst of a depression prior to my diagnosis. Just after diagnosis and following surgery, I actually experienced an improvement in mood and depression. I am not sure if it was because I was so busy taking care of everyone around me, or if it was just that it put some of my other emotional issues into a different perspective. Either way, things improved for me. I can see, however, why it could and may cause more depression, perhaps based on anxiety and concern, and just "another issue to deal with". Make sure both the doctor who is treating your depression and your surgeon are aware of your situation, and perhaps they could even consult with each other to find the best method of controlling your depression.
Best of luck,
~Dale