Re: Tipper - adrenal tumor/breathing issues
I wouldn't dismiss the surgery until I talked with the surgeon who would do the operation. Your GP vet nor the IMS are the experts in this arena - the surgeon is and the surgeon can give you the best information to use in making this decision. Where the GP or IMS may see high risk, the surgeon may say it's nothing compared to what he usually deals with and he would certainly do the surgery if it were his dog. I'm saying, don't rely on anyone but the surgeon in making this decision because he is the only one who can really tell you. The surgeon may be more qualified to tell what kind of tumor this is apt to be.
In some reading yesterday on imaging used in PDH, I found nothing that mentioned finding a micro - they all referred to seeing a macro. Now whether that is because no scan was done prior to the tumor starting to grow or whether a micro simply cannot be seen on an MRI, I haven't determined. As previously stated, it IS possible for a pup to have both PHD and ADH - even PDH with "duel" ADH (tumors on both adrenal glands) BUT these are very rare cases. Maybe someone here knows if a micro can be seen with MRI imaging? I would think a cat scan would be more apt to pick something that small up. 
If you have definitely taken the surgery off the table, then forget about it and focus on medical intervention. I don't want you to say today that surgery is out then on down the road be beating yourself up when she starts to have more problems from the tumor as it grows for not pursuing it more closely now. There will come a time when it truly is much too late to contemplate surgery. 
If you decide to take the meds route, I think I would work with the IMS from now on if they will take Tipper on a regular basis. This has gotten too complicated for a GP vet.
So, that's what I would do - talk in depth with the surgeon who would perform the surgery before taking that off the table. If he says it is too risky for Tipper, then that is no longer an option and you have no other choices but to treat with drugs. Please do check out the questions I posted - they are excellent and can help guide your decision.
I know whatever you decide, that decision will be made out of the deep love you have for Tipper and your desire to do the best you can for her. Honey, that is ALL any of us can do - the best we can with what we have to work with. When that decision is made, put it to bed (as a boss of mine would say about projects in the works) and enjoy every minute you can with that sweet girl. This very minute is all any of us have - we are not promised the next breath, much less another year or three. So it is imperative that we take time to cherish every good thing that comes our way, even if that is simply a night when our baby sleeps well. 
Hugs,
Leslie and the gang
"May you know that absence is full of tender presence and that nothing is ever lost or forgotten." John O'Donahue, "Eternal Echoes"
Death is not a changing of worlds as most imagine, as much as the walls of this world infinitely expanding.