Presentation
Painful right knee with tenderness and fever.
Patient Data
There a small well-defined lobulated intramedullary cystic lesion of the tibial metaphysis extending to the epiphysis through the growth plate. It elicits an intermediate signal on T1, high signal on PD fat sat and STIR centrally with a peripheral rim isointense to muscle on T1, hypointense on PD fat sat and STIR with a regular enhancement "penumbra sign".
Extensive surrounding bone marrow edema extending to the epiphysis and proximal diaphysis as well as to the surrounding soft tissues.
Normal appearance of the menisci, cruciate and collateral ligaments.
No pathological joint effusion.
Case Discussion
MRI features of a Brodie abscess of the tibial metaphysis with a "penumbra sign".
The penumbra sign is seen as a rim of vascularized granulation tissue surrounding a bone abscess cavity. It can help to distinguish acute osteomyelitis from other benign or malignant lesions.