Chondroblastoma also known as Codman tumor, calcifying giant cell tumor or epiphyseal chondromatous giant cell tumor is a rare tumor occurring in young patients. It commonly arises in the epiphyseal region of long bones and usually involves a single bone. Although a majority of them are benign, few can become malignant and even metastasize.
Chondroblastomas occur predominantly in the second and third decade of life and their incidence is higher amongst males . They account for <1% of all primary bone tumors  and arise from the secondary ossification centers  at the epiphyseal ends of long bones like the distal and proximal femur, proximal tibia, and proximal humerus  . They can also be found in flat bones like the acetabulum and ilium, or other sites such as the talus, calcaneus, patella , and the temporal bone .
Characteristic clinical presentation of chondroblastomas is often vague joint pain or localized tenderness, without a history of trauma. A palpable mass, joint effusion, muscle atrophy and decreased range of joint motion may also be present. Constitutional symptoms are usually absent. Fractures are rare but may occur when the tumor is large. Recurrence rates of chondroblastoma have been reported to be higher when they have a component of aneurysmal bone cyst . Chondroblastomas can be localized or can extend into the surrounding soft tissues. Some chondroblastomas behave aggressively and can recur following excision or metastasize to distant organs, especially the lungs. Deaths following widespread metastasis of chondroblastoma have been reported   .
The workup of chondroblastoma relies mainly on radiology and histopathology. On plain X-rays, chondroblastomas appear as circumscribed radiolucent lesions, with sclerotic rims and smooth or lobulated margins located eccentrically within the epiphysis of long bones, typically the humerus, femur or the tibia. Approximately 50% of the tumors have internal calcifications  . A variable amount of joint effusion is noticed in about 30% of patients . Computed tomograms (CT) are preferred to plain X-rays as they can demonstrate more accurately the relationship of the tumor to the epiphyseal and articular region, the extension of the tumor to the cortex, as well as the periosteal reaction, and the internal calcification  . CT scan can also reveal endosteal scalloping .
Magnetic resonance imaging (MRI) is performed to detect transphyseal or transcortical extension, the status of the bone marrow and the extent of the soft tissue edema  .
On histopathology, the characteristic finding in a chondroblastoma is the chicken wire pattern of linear deposition of calcification around individual chondroblasts  . The reaction of neoplastic cells to S-100 protein and vimentin can be demonstrated with immunohistochemical staining.
Differential diagnosis of chondroblastoma include other bone tumors like giant cell tumor, clear cell chondrosarcoma, chondromyxoid fibroma, eosinophilic granuloma, and chondroblastoma-like chondroma and these have to excluded on the basis of their radiological and histological characteristics.