The Tony-winning actress had been hospitalized with a serious head injury after falling on a Canadian ski slope. Richardson, 45, part of the Redgrave dynasty of British actors and the wife of Liam Neeson, was flown from Montreal to New York on Tuesday after the accident.
Richardson's career highlights included the film "Patty Hearst" and a Tony-winning performance in a stage revival of "Cabaret."
Alan Nierob of Rogers & Cowan said in a statement Wednesday night: "Liam Neeson, his sons, and the entire family are shocked and devastated by the tragic death of their beloved Natasha. They are profoundly grateful for the support, love and prayers of everyone, and ask for privacy during this very difficult time."
The head injury Richardson suffered in a skiing accident Monday produced what is often called a "walk and die," syndrome, which is usually due to delayed bleeding from an artery in the brain, said Dr. Christopher Giza, a neurologist at the University of California, Los Angeles' Brain Injury Research Center.
In such cases, the patients, like Richardson, appear normal immediately after the injury, walking and talking as though nothing happened. But symptoms can develop within an hour, causing the patients first to suffer impaired speech and vision and then to fall into a coma.
The actress most likely suffered from an epidural hematoma, in which bleeding occurs from an artery in the brain, according to Giza. Because blood in arteries is under high pressure, it can accumulate rapidly in the organ, pushing the brain to one side and leaking down into the brainstem, where it can "cause a change in mental status, the onset of a coma or, in severe cases, kill the person," Giza said. "In general, to have this kind of hemorrhage, you have to experience a significant amount of force."