I went through this last summer. For about three or four months, the vet couldn't figure out what was wrong. My lil' guy had something going on with his sinuses. Thought it was some kind of sinus infection, treated with multiple antibiotics, that didn't work, then they thought maybe it was asthma.....but then we had noticed some facial deformity on his forehead. Cat scan showed, sinus cancer. Which is rare in cats, especially older cats. My guy was 12 at the time and everything else health wise was fine with him. Because the sinus area is so delicate, they cannot remove the tumor. My vet suggested radiation. A new, more efficient radiation called Cyberknife. I live n NJ and luckily there was a hospital in Yonkers NY that had this equipment. I believe there are only maybe three hospitals in the country that do this procedure on animals. My guy is ten months out now from the radiation. He had a couple seizures back in May, a side effect from the radiation, but is on anti seizure meds now and hasn't had one since. Unfortunately after today's visit to the oncologist, we've determined that the tumor looks like it's growing slowly. They also found that his lymph node on the same side as the tumor was slightly enlarged and also on the same side found a mass growing deep within his ear cavity. Going for test tomorrow to biopsy the mass and lymph node, then we'll take it from there. My concern for you is that you said that the problem seems to be only on the one side of his nose, which was the same case with my lil' guy. Next procedure for you would probably be a CT scan. This will definitely determine whether there is a tumor or not. I hope not, but if so, I would definitely consider the Cyberknife if it's accessible to you. It's expensive....between the CT scan and the radiation procedure, it cost me almost $15,000. To me that was worth it to have my baby for another year or so.....of course after today, I'm very worried. I wish you and your kitty the best of luck and I hope it's not sinus cancer.
Healthy thoughts for your lil' one.