Acute lymphoblastic leukemia (ALL) accounts for 15-20% of childhood leukaemias, commonly affecting young children (2-10 years of age).

In children it preferentially involves the long bones, the femur being the most common site.  A variety of appearances of bony involvement may be identified on plain radiograph, one being permeative bone involvement, with a quarter having some form of periosteal reaction, which includes lamellar and sunburst types.  Extramedullary soft tissue is a feature of chloroma.

The differential diagnoses initially proposed for this case include metastatic neuroblastoma, Langerhans cell histiocytosis, lymphoma, and osteomyelitis.