The Stauffs went to see Dr. Mathern because he specializes in a particular operation called a hemispherectomy, in which he removes or disconnects half of the child's brain to stop the seizures. He told the Stauffs that Evan needed the surgery.
"It's a stunning operation," he said. "What you have to understand is that risk to the child for death and severe morbidity from the seizures is actually greater than the operation itself."
"So a child born with epilepsy, by the time they reach 40, 20 percent will be dead from their seizures," he said.
It's a wrenching decision for any parent to agree to have half their child's brain removed and risk death on the operating table, but by the time the Stauffs met with Dr. Mathern, they said they knew it was what they had to do.
"It made sense," David Stauff said. "It may seem very radical, but at the same time, it was so practical for Evan. Remove it. It's not working. It's hurting him. It will kill him. It's worth the chance."
After further tests, Mathern determined the problem was coming from the left side of Evan's brain, the side that controls speech. He prepared the family for possible side effects, such as Evan coming through the surgery with vision problems and loss of motor control on his right side.
At home in Oregon weeks before the surgery, Evan's older brothers, Patrick, 7, and Chandler, 11, seemed very supportive and optimistic of their younger brother's surgery.
"When he grows up a little ... his right eye will just be blanked," Patrick said.
"He won't see anything out of the corner of his right eye," Chandler said. "He'll be a lefty, so he'll write with his left hand."
"And sometimes he'll limp when he gets older and he walks," Patrick added.
"Yeah, he'll be different from us, and we'll still love him," Chandler said, kissing Evan.
In describing his decision to go ahead with surgery, David Stauff said, "I don't care if he can't ever walk a straight line or move his arms above his head. Just to look at each and every one of us and know who we are...That is huge."
Evan's parents brought their young son in to UCLA before dawn on Nov. 23. A surgical team went to work inside of Evan's head in an 11-hour-long surgery. Afterwards, the Stauffs visited their youngest child in his recovery room.
"We haven't had any seizures and he's smiling," Kathleen Stauff said, "just getting back to normal."
The surgery made an immediate difference for Evan, but the question remains, how can a child live with only half a brain?
Dr. Mathern explained that the brain, particularly in young children, has an incredible ability to rewire.
"There are certain functions on your brain that you can shift from one hemisphere to another," he said. "Language, for example, which in 98 percent of people is on the left side, can be moved to the right if you operate early enough."
Mathern said that a hemispherectomy patient's resulting I.Q. often depends the health of the remaining half of the brain and much damage the seizures caused before surgery. But personality, he said, is not affected.
"I have taken out right hemispheres, I have taken out left hemispheres, and the kids come out with the same personality they had before," he said. "So, I don't know where personality is."
At least 217 of these operations have been performed at UCLA, with the loss of only one child in surgery.