Radiolucent multiloculated lytic lesion in the proximal tibia. answer - it's a pigmented villonodular synovitis that decided to invade the tibia rather than grow into the joint space Differentials Giant cell tumor ( although in classical giant cell the margin is more distinct ) Aneurysmal bone cyst Simple bone cyst chondrosarcoma chondroblastoma chondromyxoid fibroma giant cell reperative granuloma brown tumor of hyperparathyroidism enchondroma ( why not ? ) and the list goes on
