Sarah Ellenberger still goes to all her high school team's soccer games. She just doesn't play anymore.

The Annapolis 15-year-old has been sidelined permanently after suffering two concussions within a week - the second of which left her in a heap on the field after she routinely hit a ball with her head, unable to remember her birthday, the day of the week or what had happened to land her in the emergency room.

The Ellenbergers didn't realize at first how serious Sarah's head injury could have been. But when they learned about "second-impact syndrome" - a rare but potentially fatal condition in which an athlete suffers a second injury to the head before a first has fully healed - they decided to keep their daughter off the field for good.

"It scared the wits out of me," said Nancy Ellenberger, Sarah's mother. "It's not going to happen again."

Debate continues in the medical and sports communities on when it is safe for an athlete to return to play after suffering a concussion. Some experts now say it may take longer for brains to heal than previously thought.

An Institute of Medicine report this year on the consequences of head injuries in soccer said that youths may be more at risk for serious injury because their brains are still developing and that coaches and parents need better training in identifying and treating concussions.

Injury to the brain

A concussion occurs when the brain is shaken inside the skull, resulting in a temporary alteration in brain function or mental status, such as loss of consciousness, dizziness or poor memory. About 300,000 sports-related concussions occur in the United States every year.

On this, neurologists and sports medicine specialists agree: Athletes shouldn't return to sports before all their symptoms have cleared up.

"Where they disagree is how long to keep somebody out - whether it's a week or two weeks or a month," said Dr. Robert C. Cantu, medical director at the National Center for Catastrophic Sports Injury Research at the University of North Carolina at Chapel Hill and author of a widely used set of return-to-play guidelines. "And there's no scientific data right now that gives one absolute indication. There is no magic marker, such as a blood test or an X-ray, that will tell the doctor when the athlete is totally over a head injury."

Symptoms of a concussion include headache, nausea, a vacant stare, disorientation, difficulty concentrating and slowness in answering questions or following directions. Depending on the severity of the concussion, symptoms can last from minutes to months.

Danger of early return

Returning to sports before the brain heals can worsen the concussion. It can also put an athlete at greater risk for another injury - to the head or any other part of the body.

"It's kind of like driving impaired," said Dr. Andrew M. Tucker, director of primary care sports medicine at the University of Maryland and chief team physician for the Baltimore Ravens. "Your reaction time may not be normal, your ability to process information in a high-speed game may be slightly altered. It'd be like playing impaired, and that's not a good thing."

The most dangerous risk of returning to play prematurely is second-impact syndrome, a sudden and acute deterioration of neurologic function due to uncontrollable swelling of the brain.

Only a few dozen cases of sudden-impact syndrome have been reported in the past 15 years, Tucker said, mostly involving male athletes in their teens or 20s in boxing, football and ice hockey. Last year, a 16-year-old rugby player from Colorado died after hitting his chin on the head of another player after several other head injuries.

"The issue is, what the heck is happening to this small number of brains?" Tucker said. "We don't really completely understand what is happening."

Nor are doctors sure what effects, if any, concussions have on a person's long-term health.

"Multiple concussions get to be a real problematic thing. What number is too many? We don't know," Tucker said. "Some brains seemingly sustain a lot of mild concussions but have no untoward effect - forever. Some brains have a few concussions and develop prolonged post-concussive symptoms where a person is really altered in terms of how they feel and function for a period of time. It's very difficult to predict who is going to be in which category."

Concussions can be hard to diagnose because there isn't always a visible sign, such as loss of consciousness, so coaches, trainers and physicians have to rely in large part on athletes describing their symptoms. Many times, players aren't fully honest, especially if they don't want to be taken out of a game. Some also think that getting knocked in the head is a natural part of sports.

Professional football and hockey teams, as well as some college and high school sports teams, are increasingly using neuropsychological testing - which measures visual and auditory memory, coordination and other brain functions - to help determine the impact of a head injury. Many teams test players at highest risk for a head injury to establish a baseline "neuro- psychological fingerprint." That way, if they are injured later, they can be tested again to see if their brain has returned to normal.

Diane Triplett, executive director of the Brain Injury Association of Maryland, said that while most trainers are conservative about returning players to the field, many parents, "weekend" coaches and even some doctors don't have enough information about concussions. Some hospital emergency rooms hand out discharge instructions to concussion patients with outdated or incomplete information, she said.

'Err on side of caution'

Jon Ferber, head athletic trainer at Mount Saint Joseph High School, said he won't let a player return unless the player has a doctor's note and has been symptom-free for 48 hours. Ferber also talks with teachers to determine whether injured players have trouble concentrating or remembering things in class.

"I will absolutely err on the side of caution, period," Ferber said. "Unless proven otherwise, it's a life-type emergency."

Cantu's return-to-play guidelines say that an athlete who has had even a mild concussion - without loss of consciousness and with symptoms lasting less than 30 minutes - should be sidelined for at least a week.

A sophomore at Broadneck High School in Annapolis, Sarah Ellenberger doesn't remember much after her first concussion Aug. 26 other than feeling incredibly sleepy. She had some dizziness the next day and headaches through the weekend but felt good enough to return to play six days later.

When Sarah headed the ball during a game, though, she crumpled to the field. She still isn't sure whether she lost consciousness, but she was taken by ambulance to the emergency room.

"It's absolutely clear to me that the first injury was not healed," said Nancy Ellenberger. "That's what freaked me out: that the second one can kill you if the first one hasn't healed."

Sarah still has sharp headaches, mostly when she is trying to concentrate, but she says her memory is fine. She has an appointment with a neurologist later this month, but her parents think the potential risk of another brain injury isn't worth sending her back into contact sports again. Sarah attends all the girls' soccer games to support her former teammates and help keep statistics.

"It's like a death," said Matt Ellenberger, Sarah's father. "It's an abrupt end. You just have to come to terms with it."

But he doesn't blame anyone for what happened to his daughter.

"I think everyone we ran across did the best they could under the circumstances," he said. "Pointing fingers is very unfair. I have no doubts this could have happened anywhere."