A subdural hematoma is the presence of blood between the dura and arachnoid mater of the meninges, so it is termed extra-axial.

In the subacute stage, a subdural hematoma appears isodense to surrounding brain parenchyma. This makes it hard to be differentiated from brain parenchyma. Note its indirect effect in the form of mass effect described above.

MRI offers more characterization of aging hematoma. It appears bright on T1 and on T2 owing to extracellular methemoglobin of late subacute hematoma.