Fibrocartilaginous Intramedullary Bone Forming Tumor of the Distal Femur Mimicking Osteosarcoma
A 9-yr-old boy presented with pain on his left distal thigh for 6 months without any trauma history (date of initial consultation: 2009-12-31). On physical examination, no palpable mass, no tenderness was identified and the range of motion was full. A plain radiograph was taken () and it showed moth eaten both osteolytic and osteosclerotic lesions in the left distal femoral metaphysis. But there was no periosteal reaction or no cortical destruction. Magnetic resonance imaging (MRI) showed T1 low and T2 heterogenous signal intensity intramedullary lesion in the metaphysis which had not crossed the growth plate and no definite cortical destruction was also identified (). A radiologist reported that this case was consistent with an osteosarcoma but the possibility of benign lesion could not be excluded. A whole body bone scan () showed mild increased uptake in the left distal femur. Complete blood count, erythrocyte sedimentation rate, C-reactive protein level and blood chemistry were all within normal limits. An incisional biopsy was performed in the belief of possible malignancy. Pathologic specimen () showed that the lesion revealed many irregular shaped and sclerotic mature and immature bony trabeculae with moderately cellular stroma composed of relatively uniform spindle cells and cartilaginous components without significant cellular atypia. A "diagnosis" was not easily made because of conflicting debates for the diagnosis were issued from the conventional osteosarcoma to low grade central osteosarcoma or benign intramedullary bone forming lesion after case conference discussion and consultations with foreign pathologic specialists. We informed all of the findings to his parents and decided to have a close observation without any further invasive procedures or surgical treatments, because the boy had a just minimal symptom of intermittent pain and the parents agreed.\nThirty-six months after initial visit, radiologic findings from the plain radiographs () and MRI findings () showed no significant interval changes of extent and morphology. A whole body bone scan showed mild decreased uptake in comparison to the initial scan (). Now he is 12-yr-old and clinically he is pain free and has no restriction of any activities until now. There is no sign of growth disturbance. He will be followed annually.