Radiographically aggressive, biopsy proven aneurysmal bone cyst (ABC) of the distal femur in a 17-year-old boy (compare the striking similarity with patient from Fig. 10). An anteroposterior radiograph of the distal left femur shows a lytic distal metadiaphyseal lesion (asterisk) of the left femur. The lesion extends into the epiphysis and adjacent soft tissues with no calcified peripheral shell (black arrow). The ABC has a wide zone of transition (white arrows) and aggressive periosteal reaction proximally (arrowhead). The lesion was biopsied twice and ABC was confirmed twice