What it means
When a tiny blood vessel leaks, the blood breaks down and leaves an iron-rich residue called hemosiderin. Iron disturbs the MRI magnetic field, so it shows up as small, very dark dots on blood-sensitive sequences called SWI or T2* (T2-star). Microbleeds are a sign of fragile small vessels, not an active bleed. By themselves they usually cause no symptoms.
When it matters
Where they sit gives clues. Microbleeds deep in the brain are mostly linked to high blood pressure. Those near the brain surface in older adults can point to cerebral amyloid angiopathy, a protein build-up in vessel walls. Head injuries can also cause them. Having many of them may raise the risk of a larger bleed, which doctors weigh when deciding about blood thinners. A single one is fairly common in older adults.
Questions to ask your doctor
- Are the microbleeds deep in the brain or near the surface?
- Does this change whether I can take aspirin or blood thinners?
- Could they come from high blood pressure or a past head injury?
