MIAMI, June 15 - An exhaustive autopsy found that Terri Schiavo's brain had withered to half the normal size since her collapse in 1990 and that no treatment could have remotely improved her condition, medical examiners said on Wednesday.

The autopsy results, released almost three months after Ms. Schiavo died after the court-ordered removal of her feeding tube, effectively quashed allegations by her parents that she had been abused by her husband. Yet the findings also questioned the prevailing theory that an eating disorder had prompted Ms. Schiavo's collapse, stating there was not enough hard evidence.

The report generally supported the contention of Ms. Schiavo's husband, Michael, accepted by judges in six courts over the years, that she was unaware and incapable of recovering. And it countered arguments by her family, who badly wanted to win custody of Ms. Schiavo, that she was responsive and could improve with therapy.

In the last months of her life, the fight over Ms. Schiavo produced a searing national debate about the rights of incapacitated people and when their lives should end if they left no specific instructions. The question of whether Mr. Schiavo should bring about his wife's death by removing her feeding tube, or whether he should cede custody to her parents, went on for seven years, reaching the Vatican, the White House, Congress and finally the United States Supreme Court, which declined to hear the case.

But the autopsy left unresolved the mystery, which haunted not just her husband and parents but ultimately much of the nation, of why Ms. Schiavo's heart stopped beating late one night when she was 26. The ensuing brain damage left her able to breathe on her own but not, most doctors said, to think or to have emotions.

"The only diagnosis that I know for sure is that her brain went without oxygen," said Dr. Jon R. Thogmartin, the medical examiner who led the autopsy in Pinellas County, where Ms. Schiavo had spent her final years in a hospice. "Why? That is undetermined."

The autopsy also found that the brain deterioration had left her blind. That finding, along with the determination that the brain damage was irreversible, caused some Republicans in Washington, who had pushed so hard for federal intervention in her case, to have second thoughts. And Democrats cited the autopsy results as proof that critics of the federal intervention had been vindicated. (Related Article)

At a news conference in Largo, near Tampa, Dr. Thogmartin said the condition of Ms. Schiavo's body was "consistent" with earlier medical findings that she was in a persistent vegetative state. Her parents, who believed she might some day eat and drink on her own or even speak, had rejected that diagnosis. But the courts accepted testimony from Ms. Schiavo's husband, Michael, that she would not want to stay alive in her condition.

"This damage was irreversible," Dr. Thogmartin said of Ms. Schiavo's brain. "No amount of therapy or treatment would have regenerated the massive loss of neurons."

Yet a lawyer for Ms. Schiavo's parents, Robert and Mary Schindler, said they still believed their daughter had responded to their voices and touch. The lawyer, David Gibbs, said the parents, who were traveling in Minnesota on Wednesday, also doubted the finding that Ms. Schiavo was blind. The Schindlers had released videos showing their daughter appearing to smile at her mother and track a balloon with her eyes.

"She had a life that was worth saving," Mr. Gibbs said.

Dr. Thogmartin said that in addition to studying Ms. Schiavo's remains, he had scoured court, medical and other records and interviewed her family members, doctors and other relevant parties. A specialist in Michigan separately studied Ms. Schiavo's heart tissue, and a laboratory in Connecticut determined that she did not have a genetic mutation that might have caused her heart to stop.

Ms. Schiavo had lost more than 100 pounds between her teenage years and the time of her collapse, and some doctors had theorized that her heart had stopped due to bulimia. Her husband even won a malpractice lawsuit on that premise, persuading a jury to award $1 million in damages on the grounds that Ms. Schiavo's obstetrician had failed to diagnose bulimia.

But Dr. Thogmartin stopped short of that conclusion. He said that while Ms. Schiavo had a low potassium level after her collapse, a symptom of an eating disorder, there was no evidence of her taking diet pills or laxatives or binging and purging.

"You end up with a 26-year-old that used to be heavy, that now lost the weight, is reveling in her thinness now, enjoying her life, and doesn't want to gain the weight back," Dr. Thogmartin said. "And if that's a bulimic, there's a lot of bulimics out there. It's just not enough."

He added that Ms. Schiavo's potassium level could possibly have dropped immediately after her heart stopped, perhaps during resuscitation efforts. Or, he said, Ms. Schiavo's habit of drinking excessive amounts of caffeinated tea might have even caused the deficiency. But unless new evidence comes to light, he said, no one will ever know for sure.

Though Ms. Schiavo went almost two weeks without her gastric feeding tube before dying on March 31, Dr. Thogmartin said she technically died of "marked dehydration," not starvation.

The autopsy also ruled out heart attack or physical abuse causing Ms. Schiavo's collapse. Dr. Thogmartin said drug overdose was unlikely, though the toxicology tests performed immediately afterward would not have detected an overdose of diet pills or caffeine.

"I don't think drugs were sufficiently ruled out," he said.

Ms. Schiavo's parents had accused Mr. Schiavo of abusing their daughter and had even produced bone scans that they said showed damage to her spine, ribs and knees. But Dr. Thogmartin said he found only one fracture on a vertebra, which he said was likely caused by osteoporosis.

Dr. Michael Baden, a forensic pathologist who used to be New York City's chief medical examiner, said the autopsy was more thorough than most and should lay to rest all rumors of foul play.

"The politicians said that if she were treated differently she might have had a different outcome," said Dr. Baden, who was not involved in the autopsy but read the report. "This shows that no matter how you treated her, there wouldn't have been a different outcome."

He added, "This doesn't close the book on the cause of this in the first place. But we know it wasn't trauma or spousal abuse. Whatever the cause, it was a natural one rather than a suspicious one."

Shortly before Ms. Schiavo's death, President Bush cut short a Texas vacation and returned to the White House late one night to sign a law allowing her parents to seek a federal court review of the case. His brother, Gov. Jeb Bush of Florida, also intervened on the Schindlers' behalf, even getting the State Legislature to pass a law in 2003 empowering him to order Ms. Schiavo's feeding tube reinserted after doctors had removed it. But the law was ruled unconstitutional, and Governor Bush eventually declared himself out of options.

On Wednesday, Governor Bush praised Dr. Thogmartin and his staff for their "careful review" and added that he would "continue to strive to protect our most vulnerable citizens."

Michael Schiavo's lawyer, George Felos, said his client felt vindicated by the results.

"For years he feels that he's been talking in the wind," Mr. Felos said. "Mr. Schiavo was pleased to hear the hard science and evidence of those findings."

Lynn Waddell contributed reporting from Largo, Fla., for this article.