I had a minimally invasive retrosigmoid AN removal. Because the tumor was large, the opening was the size of a quarter. For smaller tumors, my surgeon uses a dime sized opening. This is often referred to as "keyhole." My surgery was done completely with an operating microscope, no endoscopes. Some surgeons use endoscopes and some surgeons use both instruments combined when performing "keyhole" brain surgery.
I chose the minimally invasive approach because it involved far less time under anesthesia, no time in an ICU, faster recovery, less time in the hospital than "open" procedures, and a demonstrated success rate. My surgeon had used his own minimally invasive approach 600 times for AN's, and a similar number of times for C-P Angle meningiomas. I was in surgery less than 3 hours, in a regular neuro floor room less than 7 hours after the operation, up and walking in under 24, and discharged in under 48 hours.
The "keyhole" approach is used and described at neurosurgery centers like Johns Hopkins, UCLA, Cleveland Clinic, Mayo Clinic and around the world. I had no problem choosing minimally invasive surgery when it was presented to me, and I did have an open treatment plan presented to me by a House trained neurotologist and Barrow trained neurosurgeon team. If I had the same decison to make today, it would be the same.