A small amount of bleeding in the brain seems to be common among older individuals, according to a UC Irvine study.

Neurologist Dr. Mark Fisher and neuropathologist Dr. Ronald Kim found that cerebral microbleeds are highly prevalent in the aging brain -- and not primarily products of stroke-related injury, hypertension or neurodegenerative diseases such as Alzheimer's, as had been thought.

"Prior work relied on brain imaging to show cerebral microbleeds," Fisher said. "But in this study, deep regions of the brain were closely examined under a microscope, and nearly all subjects had evidence of small areas of bleeding."

Results appear online in the journal Stroke.

Fisher, Kim and colleagues at Harbor-UCLA Medical Center studied postmortem brain specimens from 33 individuals, ranging in age from 71 to 105, with no history of stroke. Cerebral microbleeds were identified in 22 cases -- all occurring in capillaries, the small blood vessels of the brain.

This is a substantially higher rate of incidence than that reported in MRI studies, which have shown microbleeds in 18 percent of people between 60 and 69 and in 38 percent of those over 80.

"Drugs that interfere with platelets and blood clotting, such as aspirin, are known to be associated with microbleeds seen in brain imaging studies," Fisher said. "Our findings suggest that aspirin and other platelet medications may have a different effect on the aging brain than on younger brains."

Results from the UCI study also indicate that leakiness of brain blood vessels increases with age, he said, despite the fact that a specific barrier (known as the blood-brain barrier) exists to prevent leakiness.

The areas of bleeding found in the study were very small and certainly not life-threatening, Fisher said. How they might affect intellectual and neurological function is a subject for further exploration.

Dr. Samuel French and Dr. Ping Ji of Harbor-UCLA participated in the study, which received National Institutes of Health support.