MRI
Distal lateral femoral condyle metaphyseal abscess showing T1 hyperintense rim of granulation tissue (penumbra) around the low signal fluid-filled abscess cavity with surrounding marrow edema of low signal. On post-contrast series, there's an intense enhancement of the rim and the surrounding marrow edema, associated with lateral cortical erosion and an extra-osseous abscess as well as reactive synovitis evident by diffuse synovial thickening and enhancement.