Las Vegas neurosurgeon Lonnie Hammargren said about one-fourth of the right side of the Siegfried & Roy star's skull was removed to relieve cranial pressure in the crucial hours after the Oct. 3 attack. He said Horn suffered a "pretty big stroke" but that his paralysis might only be temporary.
Horn remained in critical condition Thursday at University Medical Center in Las Vegas. Hammargren said it was unclear when Horn would undergo surgery to return the skull piece.
Hammargren, a former Nevada lieutenant governor, told the Las Vegas Review-Journal that he was commenting about Horn's treatment to correct misinformation about the procedure.
Hammargren didn't operate on Horn, but said he talked with Horn's surgeon, Dr. Derek Duke, about Horn's treatment.
Hammargren denied published reports that Horn, 59, underwent a radical procedure called a hemicraniectomy, involving surgical removal of half the skull.
He said Horn's surgeons instead performed a decompressive craniectomy, a more common procedure involving removal of about one-quarter of the skull.
"Dr. Duke did exactly the operation he should have," Hammargren said Wednesday. "Otherwise, Roy would be dead."
Hammargren said surgeons can remove a portion of the skull to give the brain room to expand following brain surgery, trauma, stroke or other medical problems causing the brain to swell.
The removed portion of the skull can then be surgically placed in the abdomen or frozen until it can be replaced, Hammargren said. He said he was told Horn's skull had been implanted in a pouch in Horn's abdomen.
Hammargren confirmed that Horn suffered a stroke and was paralyzed on the left side after the tiger attacked his neck.
"He had a pretty big stroke," the neurosurgeon said. "We just don't know yet. Fortunately, the stroke didn't hit on the side where he talks, thinks and remembers. He can still comprehend things and do things."
The 7-year-old male tiger that attacked Horn was released Tuesday from quarantine after 10 days of isolation. Clark County officials said they determined it did not have rabies.
MGM Mirage officials said the animal, named Montecore, will continue to live at the Secret Garden, an animal habitat at The Mirage hotel-casino.