Faster growing tumours tend to have poorer success rates for both surgery and radiation...
Dr. Lunsford, the man who introduced the Gamma Knife to the USA, told me the exact opposite.
Dr. Jason Sheehan, a surgeon at the University of Virginia who was trained by Dr. Lunsford, also told me the exact opposite.
They both expressed to me that faster growing AN's respond better to GK.
Furthermore, Dr. Schwartz at the House Ear Clinic in Los Angeles also indicated (in my situation) that my fast-growing AN had no influence on the outcome of the success rate. The experience of the surgeon and team is what most influences the success rate, independent of the growth rate of the tumor.
At the end of the day, like many issues regarding AN's, it all depends which doctor you talk to.
Dr. Chang at Stanford was the only one whom I encountered that pointed me in the direction of microsurgery citing concerns of my fast-growing tumor and my suicidal tinnitus.