Trepanation was the act of surgically drilling a hole in a patient's skull.
In 1986, after a fundoscopic examination of an injured Pavel Chekov, doctors were about to perform "a simple evacuation of the expanding epidural hematoma". Leonard McCoy, realizing what that entailed, replied that "drilling holes in his head's not the answer". (Star Trek IV: The Voyage Home)
In 2257, Jett Reno proposed trepanation be performed on Sylvia Tilly so that a cortical implant could be inserted. Paul Stamets asked if she planned to fix it with duct tape afterwards. (DIS: "An Obol for Charon")