Other factors associated with recovery include the patient's age, the cause of the coma, and the depth of the coma ranked on the Glasgow Coma Scale. But even if those factors offer a poor prognosis, a less-than-6-millimeter shift in symmetry could trump the other variables, Kowalski said.
"It's never 100 percent; every case is different," he said. "But we think that the 6 millimeters is a good guideline to keep in mind."
To quantify the shift, the researchers measured two areas in the brain: From the septum, located near the top of the head, down the center of the brain to determine the midline shift, and the pineal gland, located above the roof of the mouth, to determine side to side movement of the brain stem. In both cases, they found that for patients who had less than a 6-millimeter shift -- or if the displacement moved back to within 6 millimeters at a follow-up CT scan -- the association with awakening was strong (and if the shift grew, the patient was much less likely to waken.)
"The implications are that it gives options for treatments," Geocadin said. "And we do have those treatments; we just didn't know to what extent to push them."
Current treatment protocol involves injecting the brain with a salty solution that's known to push it back into position -- or surgical relief of pressure that encourages repositioning. Using the 6 millimeter designation should give clinicians guidance when using the techniques, the researchers said.
"It was like we were driving down the street without a speedometer," Geocadin said. "Now we have a parameter."
The emphasis in current practice, Young said, is to control cranial pressure, while surgery is usually reserved for life-saving situations. After reading the study, he said clinicians may need to be more aggressive in minimizing the midline shift, including using surgical measures.
"We've reserved it for extreme measures, but it could be used to improve outcomes as well," he said, noting that he hasn't seen the salt solution work as well as surgery to shift the brain.
A future study, he said, would be key to compare similar, randomized patients treated either with surgery or standard care.
One limitation of the study, Kowalski noted, was that they were not able to follow the patients after they left Johns Hopkins.
"The key thing to remember," Geocadin said, "is unless the patient wakes up, everything else is a no-go. Once you start waking up, then you can start building."