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

Abstract

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 tumor.

A 12- year old girl presented with limping, swelling and pain in the mid of the left femur. Radiography showed a 12 cm long intraosseus expansion and lamellated periosteal reaction. 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. On histological grounds fibrous dysplasia, desmoplastic fibromas and low-grade fibrosarcomas had to be considered as differential diagnoses. The diagnosis of low-grade central osteosarcoma was made and confirmed by reference pathology. The tumor 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 adequate treatment, despite a wide range of differential diagnoses,  a multidisciplinary approach is essential.