Giant Cell Tumor
The giant cell tumor is found relatively frequently, but malignant transformation is rare, occuning in fewer than 10% of lesions.
There is a slight female preponderance, and the peak incidence is between 20 and 49 years of age. It is rare before closure of the growth plate or after 50 years of age.
This tumor is localized to the metaphysis. Ninety percent of cases involve the long bones, where the lesion is localized to the metaepiphyseal region. More than 50% of giant cell tumors involve the knee (distal femur and proximal tibia metaepiphyseal region).
Other bones that can be affected include, in order of frequency, the distal radius, sacrum, distal tibia, proximal humerus, pelvis, and proximal femur, Other sites are rarely affected.
On CT scans, giant cell tumors appear as lytic lesions with thinning and erosion of the cortex. A sclerotic margin may be present between the tumor and the normal marrow cavity. On MR images, giant cell tumors are well defined with a low-signal-intensity rim or halo surrounding the tumor. On TI-weighted images, they have intermediate signal intensity and are usually homogeneous; on T2-weighted images, they have intermediate to high signal intensity and may be inhomogeneou. Focal areas with increased signal intensity may be seen on both TI-weighted and T2-weighted images and represent hemorrhage. Fluid-fluid levels, often seen in aneurysmal bone cysts and telangiectatic osteosarcomas, are present only rarely in giant cell tumors.
Both CT and MRI accurately demonstrate the intraosseous and soft tissue extension of the tumor; CT is better at showing cortical destruction, whereas MRI is better at demonstrating intra-articular involvement as a result of its multiplanar capabili