Inexplicable breathing problems

Question
My otherwise insanely healthy 8 year old bunny started experiencing breathing problems a couple months ago. He's had a battery of tests and examinations by three excellent rabbit vets but there's no answer to what he has and it seems to be getting worse. He's had: a (clear) lung x-ray (and his heart is in good shape), a physical exam of his teeth (no problem with them), a CT scan (which showed severe swelling of the throat and his windpipe getting cut off regularly which probably is the cause of the breathing difficulties, two ultrasounds which were inconclusive other than showing unusual amounts of bacteria. He was on Zenaquin for 21 days, then after the CT scan he was on Metacam and then after the second inconclusive ultrasound he was prescribed pencillin injections every three days and just last Thursday oral prednisone.  Perhaps he would have suffocated already without these meds but they don't seem to be making him better and the vet is baffled by what it could be. It's horrible to watch -- his breathing gets more labored by the day (sounds like a child trying to breathe through a stuffed-up nose and sometimes like coffee percolating), he almost always gags when he drinks his water, sometimes he appears to choke on his food (I've been hand feeding him for weeks to make sure he finishes one mouthful before he starts the next and that helped for a while but now not as much), and though he still appears "happy" most of the time, with good appetitie etc. sometimes he's not. Nights are often the worst and in the last week I thought he was on the verge of dying at least half a dozen times but so far he seems to somehow pull through.
Surgery doesn't seem to be a good option because it's kind of going in blind not to mention I'm worried about the potential for the pain and recovery process. I would ask his vet to more seriously consider surgery as an option if there was something he knew he was going in there to fix or something he knew he could find.
Have you ever heard of a similar case to my bunny? I'm heartbroken at my inability to find an answer and though on one level I've accepted the fact that I'm indeed already losing him and it's just seems to be a matter of time, on another level he's so healthy otherwise it just seems wrong to give up. Thank you.

Answer
Dear Julie,

Wow, this is a terrible problem.  Just about any suggestion I thought about when I was reading...turns out your vets tried it already.  

I agree about the surgery.  Unless you know what there is to operate on, what would be the point?  Is it possible that this is an abscess in the throat?  If so, is it possible to do a needle biopsy to get a sample for culture and sensitivity testing?

At this point, since you've tried both bicillin and zeniquin, I'd wonder if injectible chloramphenicol might be something to try.  Or Amikacin.  But those, too, are shots in the dark.  And they'd be effective only if this is an abscess, not a tumor or some other strange problem.

The only thing I can think of to keep this at bay would be corticosteroids to reduce the swelling.  But how long can one keep that up without damage?  I guess the main thing is to keep him comfortable.

The only reason I might consider surgery would be to possibly try to get a biopsy (preferably a minimally-invasive needle biopsy) and send the tissue sample to a good histopathology lab to see if anything shows up there that couldn't be seen with the other methods you've tried.

Other than that, I'm afraid I'm as stumped as you and your vets.  I certainly hope you can get to the bottom of this, and if you do, please let me know the outcome, if you have time.

I'm sorry I can't be more help.

Sincerely,
Dana