The bone window of this CT scan shows an aggressive type multi-lamellated, elevated and interrupted periosteal reaction.
Endosteal scalloping is also evident and involves most of the femur's diaphysis, but most obvious at the lower third.
A focal area of frank cortical breach is also seen at the medial side of femur, opposite to which the muscles are displaced away by a heterogenous lobulated mass (better seen on the soft tissue window), hinting significant soft tissue involvement and possible acute hemorrhage.
IMPRESSION: aggressive tumor with significant soft tissue component.
DDx: Ewing sarcoma osteosarcoma osteomyelitis metastasis.