Hi,
I have had the same situation almost. I had been diagnosed with a tumor in 2015 and the size of the tumor was over 26 MM, so not as big as yours but still very big. They did surgery and brought it down to 16mm. They wanted to do Gamma but I was advised against it as I too was in my 30s and the tumor was too big for my new doctor to recommend as he wanted to wait and see if it would regrow. Basically explained that the size of the tumor + how long I would need to be under gamma knife radiation had some risks 30-40 years from now. Long story short the tumor didn't seem to be regrowing but in 2018 they felt it might have but weren't sure, and last June they confirmed it has grown back to 19+mm and will require surgery again. Last time they also wanted to be careful due to the facial nerve but apparently hadn't removed as much as they should have. My new Surgeon from Stanford is an expert on the tumor and said it does have a chance of regrowing in people that are in their 30s-40s even with radiation treatment. It isn't guaranteed but it is a lot higher than say if we were in our 60s or 70s. Sadly this tumor isn't as well understood as say cancer and people like us in our 30s don't commonly get the tumor so most of the research is on people much older. If you are planning on seeing someone in the USA, I recommend Dr. Jackler at Stanford, as he is my surgeon. He is going on sabbatical at the end of this year but he is very knowledgable and kind. He explains things very well in a short amount of time but has constantly responded to me over the years when I panic over something and saved hearing in my good ear. I originally went to him in 2015 but elected to do my surgery at UCSF.
He recommends I wait after reviewing my MRI in 2018 but then saw that in 2019 it was causing malformation and explained that if we did, it would make the surgery harder and he wouldn't be able to do it, the tumor wouldn't kill me if I waited but could cause health issues as well. I want him to do the surgery so I decide to not wait longer than 6 months.
Unfortunately, I don't know any doctors in your part of the world that I can recommend as I live in the states, but I do recommend getting a second opinion about if you should wait, get surgery or radiosurgery again. If you do contact Dr. Jacklar feel free to let them know Gregory Frank recommends him
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I almost forgot I was also told that I should do Radiosurgery or Gamma knife after my surgery before I had a complication and that it wasn't recommended when I got a second opinion from Dr. Jackler because of the size of the tumor. However, when I went for the consultation I was told there was a chance that the tumor could regrow and they would need to do this all over again. The last surgery left me deaf in my right ear, and I am hoping this one will not leave me with permanent changes or issues or even major complications like last time or worse. But I may have to do Gamma knife as well if they can't remove it all but can make it small enough to be much safer. (what size is safer I don't know to be honest)
Sorry to hear you too have to go through all this again, but hopefully knowing you aren't the only one will give you some comfort. I should have gone with Jackler in the first place but there is no way to know if it would have made a difference or not.
Also if you do get a second opinion make sure to write down all the questions you have. For Jackler I had to wait for a few hours in the waiting room and in the patient room for him as he only has appointments on Tuesdays and is very busy, but when he entered the room he would leave quickly unless I had questions, then he would patiently wait and answer all of the questions I had and my mom or uncle had as well. For any doctor, you go to make sure you have your MRI images and dr notes from your surgery sent to them or with you when you go see them as they will want to review all of that.