ari s nose, a so-called endoscopic skull based surgery, to reach and remove the tumor. to get there, they first had to come here, stanford s virtual reality center, where ari s brain and tumor were precisely mapped out surgeons spent hours practicing in a virtual o.r. and on a 3d printed replica of ari s skull. if you go one millimeter beyond and you re not careful, you can hit the carotid artery and get a major bleeder. reporter: on surgery day, the stakes and tensions were high. i m bawling i can t handle it. it s too much. reporter: for 16 hours doctors removed the tumor piece by piece. now months after the high stakes operation the young lion the ellmans once feared they would lose, has come roaring back to life giving other families hope that the impossible is now possible. ayman mohyeldin, nbc news, palo alto, california