Presence of hematological disorders, including anti-coagulation (this patient was on warfarin), can alter the way blood clots and thus change the appearances of a subdural hematoma, although this depends on numerous factors including the degree of coagulation impairment, timing of imaging etc..).

This same appearance can be seen in acute on chronic hematomas (i.e. an acute bleed into a pre-existing chronic collection or subdural hygroma).

As not previous imaging is available in this case, it is possible that this, in fact, represents an acute on chronic hemorrhage rather than merely an acute anticoagulated bleed.