Traumatic Head Injuries

At first, Natasha Richardson said she felt fine after she took a spill on a Canadian ski slope. But that's not unusual for people who suffer traumatic head injuries like the one that killed the actress.

Doctors say sometimes patients with brain injuries have what's called a "lucid interval" where they act fine for an hour or more as the brain slowly, silently swells or bleeds. Later, back at her hotel, Richardson fell ill, complained of a headache, and was taken to a hospital. She died Wednesday in New York.

An autopsy Thursday showed that the 45-year-old actress hit her head, which caused bleeding between the skull and the brain's covering, resulting in what's called an epidural hematoma. It's a type of injury often caused by a skull fracture.

Because of that lucid interval, doctors always tell patients who seem OK after a brain injury to have someone keep a close eye on them, in case symptoms emerge.