What is a differential for a lytic patellar lesion?
Benign lesions: Giant cell tumor (GCT), Chondroblastoma, Aneurysmal bone cyst (ABC). Malignant lesions: Osteosarcoma, metastases.
Axial CT images of the knee in a bone window show a well-defined lytic lesion involving most of the patella with cortical thinning and focal cortical breaks, compatible with giant cell tumor.
Moderate knee joint effusion.