Terri Schiavo died of the effects of a profound and prolonged lack of oxygen to her brain on a day in 1990, but what caused that event isn't known and may never be, the physician who performed her autopsy said today.

A meticulous study of the organs, fluids, bones, cells and medical records of the Florida woman who became a cause celebre over the "right to die" also found that her brain was severely shriveled and weighed about half that of a normal adult's. The damage to it "was irrecoverable, and no amount of treatment or rehabilitation would have reversed" it, said pathologist Jon R. Thogmartin, who is the chief medical examiner for Florida's sixth judicial district.

The damage was especially severe in the region responsible for vision, making her functionally blind, he said at a news conference in Florida.

Schiavo died March 31 at age 41 in a hospice in Pinellas Park, Fla., 13 days after a feeding tube was removed from her stomach under a court order. Her husband, Michael Schiavo, had waged a seven-year legal battle against her parents, Robert and Mary Schindler, to have the tube removed on grounds that his wife would not have wanted to be kept alive by such means. The Schindlers, backed by anti-abortion and right-to-life groups, rejected that argument and asserted that their daughter was responsive to them, wanted to live and could improve.

The autopsy essentially supported Michael Schiavo's contention that his wife's brain damage was irreversible and that she had no cognitive ability. It also refuted claims by some of his harsher critics that he had abused her.

Michael Schiavo's lawyer, George Felos, later told reporters, "Mr. Schiavo was pleased to hear the hard science and evidence of those findings."

Felos said Michael Schiavo intends to release certain autopsy photos of Terri Schiavo's brain "in the near future" in hopes of putting to rest any lingering doubts about her mental capacity. He said the photos would allow the public to "see the profound atrophy that was mentioned in the report."

In Washington, White House spokesman Scott McClellan said the autopsy report did not change President Bush's view of the Schiavo case, in which he and Congress had tried to intervene with the aim of restoring her feeding tube and prolonging her life.

"No . . . it doesn't," McClellan said. "Our thoughts and prayers remain with her family and friends. The president was deeply saddened by this case."

A lawyer for the Schindlers, David Gibbs III, said today his clients continue to believe that before her death, their daughter "was demonstrating a will to live."

Among other findings, the autopsy either ruled out or greatly diminished the likelihood that Schiavo lapsed into a coma 15 years ago as a result of strangulation, beatings, drug overdose, eating disorder or a rare molecular heart defect. All had been mentioned since she collapsed at age 26.

Asked at today's press conference whether there was any evidence of neglect or abuse of Schiavo, Thogmartin answered firmly: "No."

But he was unable to shed any new light on what caused the 1990 collapse that left her incapacitated. Asked whether the cause will ever be known, he said: "I don't know."

He also said that even if the Schindlers' request to give Schiavo food and water by mouth had been granted after the feeding tube was removed, she still would have died.

"Removal of her feeding tube would have resulted in her death whether she was fed or hydrated by mouth or not," Thogmartin said. He said a review of Schiavo's medical records confirmed to him that she was "not a candidate for oral hydration or nutrition," and couldn't take enough by mouth to sustain life.

"She died of marked dehydration," he said. "She did not starve to death." As measured by the balance of salt and water in her body fluids, the dehydration was the most severe he had ever seen. This attested to Schiavo's robust underlying health, and in particular the strength of her heart, the pathologist said.

A toxicology study found only "therapeutic levels" of acetaminophen (the pain reliever also sold as Tylenol), and no evidence Schiavo was given any substances that "accelerated the dying process," he said.

Examination of the heart showed no evidence of damage from a heart attack. A study of her genes by a Connecticut company called Genissance found no evidence of the mutations causing long-QT syndrome, which is an increasingly well-recognized cause of sudden cardiac death in otherwise healthy young people.

The brain examination was "consistent with a persistent vegetative state," said Stephen J. Nelson, a neuropathologist who was a consultant to the medical examiner's office.

Some advocates argued that Schiavo was "minimally conscious" -- a recently formulated condition defined as a notch above "persistent vegetative state." Both states, however, are diagnosed purely on the basis examination of the living patient. They can't be confirmed with certainty on the basis of autopsy findings.

Thogmartin was especially skeptical about the long-running theory that Schiavo collapsed because of a severe electrolyte imbalance brought on by a long-standing eating disorder. Although Schiavo had lost about 100 pounds by dieting in the years before her death, she never said she had an eating disorder and no one ever witnessed her bingeing and purging.

Instead, the principal evidence for that theory was a very low level of bloodstream potassium when she was admitted to the hospital about an hour after being found unconscious. Vomiting and laxative abuse can cause this condition.

Normal blood serum potassium is 3.5 to 5 millimoles per liter. Schiavo's was 2, a level that can cause the heart to beat weakly, or stop. However, intravenous fluids and the heart stimulating drug epinephrine -- both given in large quantities in an effort to revive the young woman -- can lower potassium. He suspects that's the explanation.

"Once you eliminate the potassium problem, you end up with a 26-year-old who used to be heavy, who had lost a lot of weight and is reveling in her new looks," Thogmartin said. "If that's a bulimic, there are a lot of bulimics out there. It's just not enough."

He also said that toxicology studies done when she collapsed Feb. 25, 1990, found no evidence of drugs.

Schiavo was reportedly a heavy tea-drinker. Overdoses of caffeine can cause low potassium and, on occasion, heart rhythm abnormalities. Caffeine wasn't tested in the drug-screen. However, Thogmartin said because Schiavo's collapsed occurred in the morning, it seemed unlikely to him she could have consumed enough caffeine for that to be the reason.

The autopsy was performed the day after Schiavo died. It included 72 photographs of the outside of her body; 116 photographs of internal organs; 58 X-ray views before the autopsy and 28 during and after it -- 274 images in all.