Central low-grade osteosarcoma with an unusual localization in the diaphysis of a 12-year old patient

Low-grade central osteosarcoma is a very rare subtype of osteosarcoma with a predilection for the metaphysis of long bones and a peak incidence in the 3^rd decade of life. Absence of specific clinical symptoms and a good prognosis after wide resection are the characteristics of this entity. Chemotherapy is not indicated in this highly differentiated tumour. A 12-year old girl presented with limping, swelling and pain in the mid of the left femur. Radiography showed a 12 cm long intraosseous expansion with lamellated periosteal reaction and contrast medium enhancement in MRI. Although radiology led to the differential diagnoses of Ewing’s sarcoma, osteomyelitis and fibrous dysplasia, the histological specimen showed a hyopocellular spindle-cell proliferation arranged in fascicles with mild cytologic atypia and only single mitotic figures. In synopsis with radiology the diagnosis of low-grade central osteosarcoma was made and confirmed by reference pathology. The tumour was resected with wide margins and reconstruction was performed with a vascularized fibula, a homologous allograft and a plate. Staging was negative for recurrence and metastasis at a follow-up of 16 months. Low-grade osteosarcoma accounts for only 1% of all osteosarcomas with a peak incidence in the 3^rd decade. The diaphyseal localization and the young age make this case special. To achieve the correct diagnosis of this rare low-grade entity and thereby the adequate treatment, despite a wide range of differential diagnoses, a multidisciplinary approach is essential