metastasize, usually to a lung, which may be benign metastasis, Plain radiograph is still the main method of diagnosing giant cell tumour. But MRI and CT scans are useful for staging and surgical planning. CT is more superior than plain radiograph in delineating the tumour outline, its extension into structures outside the bone, determining the involvement of bony cortex and tumour recurrence. CT scans show features such as thin and expanded bony cortex, with or without bony matrix calcifications, and fluid levels due to aneurysmal bone cyst or bleeding within tumour. However, axial views of the subarticular bone (bony area adjacent to the articular cartilage) is not accurate due to voxel signal averaging. MRI is superior than CT on delineating the tumour because of its better contrast resolution and imaging in multiple planes. MRI is also useful in determining the extension outside the bone and evaluating the involvement articular surface, skip lesions within bony matrix, and medullary cavity. However, bony cortex destruction is better demonstrated on CT scan. On MRI, the mass generates intermediate to reduced signal intensity on T1-weighted images, and increased signal intensity on fluid sensitive MRI images such as short tau inversion recovery (STIR). The mass enhances after intravenous gadolinium administration. Differential diagnosis A number of tumors have giant cells, but are not true benign giant-cell tumors. These include, aneurysmal bone cyst, chondroblastoma, simple bone cyst, osteoid osteoma, osteoblastoma, osteosarcoma, giant-cell reparative granuloma, Giant-cell tumor of the tendon sheath and brown tumor of hyperparathyroidism. Treatment General treatment regimens have not changed much in the past 30 years, in part due to the lack of randomized clinical trials. Surgery is the treatment of choice if the tumor is determined to be resectable. Curettage is a commonly used technique. The situation is complicated in a patient with a pathological fracture. It may be best to immobilize the affected limb and wait for the fracture to heal before performing surgery. Patients with tumors that are not amenable to surgery are treated with radiation therapy. However caution is employed since a majority of recurrent tumors with transformations to the malignant sarcoma phenotype have been in patients receiving radiotherapy for their primary benign lesion. Pharmacotherapy for GCTOB, includes bisphosphonates such as Zoledronate, which are thought to induce apoptosis in the MNGC fraction, preventing tumor-induced osteolysis. Indeed, in vitro studies have shown zoledronate to be effective in killing osteoclast-like cells. More recently, humanized