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Late Subacute Hemorrhage

Time course: ~1 week - months

T1WI: Hyperintensity

T2WI: Hyperintense with Hypointense rim

Late Subacute Hemorrhage

Methemoglobin is less stable than deoxyhemoglobin.

The heme group is readily lost from the protein molecule.

Free heme, peroxide, and superoxide can result in RBC lysis.

As cell lysis occurs, proteins degrade and the remaining extracellular methemoglobin is diluted.

Late Subacute Hemorrhage

Why is there T1 hyperintensity? Even very low concentrations of heme containing methemoglobin result in T1 shortening.

Why is there T2 hyperintensity? RBC lysis results in loss of local field homogeneity. Protein concentrations are decreasing.

Why is there a rim of hypointensity? Iron containing molecules such as hemosiderin and ferritin accumulate within macrophages.

These molecules are rendered “superparamagnetic.”