Brodie abscess

Well-defined eight-shaped lytic lesion of the distal femoral metaphysis surrounded by a thick dense rim of reactive sclerosis, oriented along the long axis of the bone and extending to the epiphysis through the growth plate.

On the MRI sequences the  well-defined lesion has an intramedullary location within the femoral metaphysis, extending to the epiphysis through the growth plate. It displays a low signal on T1, heterogeneous high signal on PD fat sat and T2 with a peripheral rim isointense to muscle on T1, hypointense on PD fat sat and T2 with a regular enhancement "penumbra sign". No evidence of intra-articular extension. Mild surrounding bone marrow edema is noted.