I'm interested, too, but it might be a loose term - sometimes people say "non-invasive" to mean "minimally-invasive" or such. So something that involves opening the skull and placing electrodes on the surface of the brain can be considered "non-invasive" to the brain matter, and endoscopic endonasal surgery is much less invasive than going through the skull.

In fact, "non-invasive operation" is oxymoronic, because an operation or surgery is a medical treatment that is invasive.