More surprisingly, the study found that strokes also were occurring undetected in children who do not have sickle cell but have other conditions that can cause anemia, such as cancer, kidney failure or blood loss from trauma such as a car crash.
Some of them have what researchers described as the brains of 80-year-olds when they were only 5 or 10.
"I don't think there's any reason to panic," but doctors need to consider the possibility of stroke when treating any child with severe anemia, said Dr. Michael Dowling, a pediatric neurologist at the University of Texas Southwestern Medical Center in Dallas.
The study involved only 52 children at one hospital, but experts in the field believe the findings have wide relevance. At the study hospital alone, Children's Medical Center Dallas, 1 percent of all admissions, or about 400 children over 2 1/2 years, were for severe anemia, said Dowling, who led the research. He presented results Friday at an American Stroke Association conference.
Out of these 400 children, doctors enrolled 22 with sickle cell and 30 children with other causes of severe anemia in the study. These 52 agreed to be tested with a newer type of MRI, or magnetic resonance imaging scan, that can detect signs of stroke and tell whether it's a recent one or an older one.
Doctors found fresh strokes were occurring in 4 of the 22 children with sickle cell, and 2 of the other 30 kids.
Alarmingly, they saw signs of "silent strokes" in 3 of the 22 sickle cell and 7 of the 30 others. These are strokes that didn't cause obvious symptoms, such as weakness on one side, but have still damaged the brain because of too little oxygen due to the severe anemia.
"We wouldn't have noticed it" without the MRIs, Dowling said. "Some may be reversible with quick transfusions" if doctors recognize it while treating the main cause of the anemia, such as blood loss from an accident.
A federal grant and several foundations sponsored the study. Dr. Robert Adams, director of the Medical University of South Carolina Stroke Center, said the study confirms that stroke is a major risk in kids with sickle cell and extends it to other children with severe anemia.
Parents and doctors need to be aware of symptoms of severe anemia: a child who is pale, tired, possibly with a rapid heartbeat.
"It is something that is very easy to check," with a simple finger clip device that measures hemoglobin, the substance in red blood cells that carries oxygen throughout the body, he said.