Rapidly growing giant cell tumor of bone in a skeletally immature girl.

Giant cell tumor of bone (GCTB) in skeletally immature patients is rare, and little is known regarding how fast GCTB can grow. We report a case of a 10-year-old skeletally immature girl with pathologically proven GCTB with obvious growth plate invasion that showed surprisingly rapid growth over only 14 days. A radiograph of the left knee revealed well-circumscribed, geographic bone destruction at the distal metaphysis of the femur with a focal cortical defect, suggesting a pathologic fracture. No abnormal mineralization or periosteal reaction was seen. A CT without contrast and an MRI demonstrated a homogeneous lesion with cortical disruption posteriorly and laterally with a slight soft tissue extension. Biopsy showed numerous multinucleated giant cells and spindle-shaped mononuclear cells without any sign of malignancy, suggesting GCTB. However, rapid lesion enlargement and destruction of the surrounding cortex were noted 14 days after biopsy. Considering the amount of bone destruction, traditional treatment of curettage and bone cement would not suffice to sustain structural strength. In addition, considering the patient's age, the tumor location, and the aggressive course, a malignant tumor, especially a giant cell-rich osteosarcoma, could not be excluded. Therefore, en bloc resection, including the growth plate and prosthetic replacement, were performed. Confirmation of GCTB was made from a pathologic evaluation, and a breach to the growth plate was identified. Since very little inflammatory reaction, degenerative change, or aneurysmal, bone, cyst-like change was found, the growth plate invasion was confirmed as due to GCTB extension, not due to the preoperative biopsy.