Paul, yes you can get a study that shows evidence of just about anything! That makes in hard for us ANers!
Those three papers are all from a single hospital in Marseille France and by the same authors. So its the one source.
I went through my papers last night and you can certainly get any answer you would like about gamma knife and hearing. There are papers that show that gamma knife is protective for hearing loss and some that show there is no difference or accelerates hearing loss:https://www.ncbi.nlm.nih.gov/pubmed/25771841https://www.ncbi.nlm.nih.gov/pubmed/25850598
I'll quote a passage from the second paper:Active treatment with microsurgery or gamma knife surgery did not appear to be protective, because patients who were observed had the greatest probability of durable hearing. Patients in the surgical series had the greatest hearing loss.
Two more papers of interest are:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4831944/pdf/nmc-56-186.pdfhttp://thejns.org/doi/pdf/10.3171/2016.7.GKS161494
The first paper (Fig. 2) shows a linear drop in hearing preservation out to 4 years and stabilizing thereafter at ~55% hearing preservation. The second paper (Fig. 3) shows a steady decline forever. At 10 years only 24% preserve hearing and at 15 years only 12%. It just keeps getting worse. Unabated.
My conclusion is that if you have a vestibular schwannoma, you will probably loose you hearing no matter what path you take. There are just ways to speed up the process.
Getting back to the three cited papers from Marseille, they had a failure for conservative management of 74% and growth for 77% of tumors. The "conventional" wisdom is that two-thirds don't grow (I believe it is closer to three-quarters don't grow - and of course I can provide papers as evidence!). Nobody is talking about only one-quarter of vestibular schwannoma tumors don't grow! Also, 74% failure rate has to be compared to https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1502035/pdf/sbs16095.pdf
. Here only 7.6% failed conservative management. Are the first set of papers over treating or the second paper undertreating. I can imagine overtreatment, but how do you undertreat with no negative outcome. For this reason I put less weight on the Marseille set of papers.
From my extensive research, there are reasons for gamma knife (a large AND rapid growing tumor), but if all you are after is hearing preservation, gamma knife just makes things worse (and you have to content with the possibility of communicating hydrocephalus, malignant transformation and new deficits). There may be a case for a rapid growing tumor that is not large, but here you are gambling.
It takes a very good understanding of where errors, biases and conflicts can occur in articles to know what is going on. Having a vestibular schwannoma is a serious event, but understanding the literature is a bigger problem. Hercule Poirot have a field day.
My final comment is that there is no interest in solving the problem. Step one in arriving at the correct picture would be to establish the natural growth of the tumor. If I were to run an experiment in three different locations around the world with 100 patients each I would get the same answer for natural growth. From this base we would be able to solve the mystery that is a vestibular schwannoma. In all these decades we still do not have an answer to the fundamental question, what percentage of ANs grow?