If you can let me know the general area you are located in I might be able to help find an actual avian vet. Birds can get tumors both cancerous and fatty (among others) and from what you are describing this sounds more like a possible fatty tumor (I'm not a vet and have heard of air pockets but not really like what you are describing!). I would really suggest getting a second opinion and would be happy to try helping locate an avian vet near your area.