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Case Report | Discussion

Case report:

A 14-year-old boy presented with the complaints of pain in the right shoulder since three months associated with minimal restriction of movements. The physician had advised a radiographic examination to rule out any local pathology.

The radiograph of the right shoulder showed an eccentrically located, 7-8 cms sized , spherical, osteolytic lesion with well-defined margins at the epiphyseal end with no involvement of the joint cavity. There was no evidence of periosteal reaction. The zone of transition was narrow.. The cortex of the lesion was thinned out. The scapula & the clavicle were unremarkable. (Fig 1,2)

Fig. 1	Fig. 2

For further evaluation, a CT scan was performed. This showed an expansile osteolytic lesion measuring 7 X 4 cms at the humeral epiphysis with cortical irregularity & few specks of calcification within the lesion. The 3-dimensional CT showed no joint involvement. ( Fig . 3,4,5).

Fig. 3	Fig. 4
Fig. 5

These findings suggested the diagnosis of a benign tumor. In view of the epiphyseal plate location and calcification, a chondroblastoma was considered most likely.

To confirm the diagnosis, histopathologic evaluation (Fig 6)of the lesion was performed. This microscopic examination revealed broad areas of both mature & immature cartilaginous cells – chondroblasts-associated with a scanty chondroid matrix with pericellular deposits of calcification that appeared like a "chicken – wire".

 

Fig. 6

Discussion

Chondroblastoma is a rare primary bone tumor of chondrogenic origin seen in younger individuals before epiphyseal closure and usually has origin from the region of the chondral plate of the long bones & the secondary ossification centers – such as greater trochanter of the femur, humeral tuberosity etc. The sites of chondroblastoma seen are distal femur, proximal tibia (17%), proximal femur (16%), proximal humerus (17%).

Radiographic features:

This tumour is medullary in origin in more than 90% of cases. It is eccentrically located always touching the epiphyseal plate. The size of the lesion varies from 1 to 10 cms with spherical / oval shape. In most cases, there is complete bone replacement, which gives an uniform lucent appearance to the interior part of the lesion. In only 1/4^th cases, tiny calcific flecks / strands may be present. The margin of the tumor is smooth & well defined. The cortex of the lesion is usually thinned out & occasionally there is complete destruction of the cortex which may simulate giant cell tumor / fibrosarcoma. Soft tissue swelling is usually present. Invasion of the joint is rare. The tumour shows hypervasularity on angiographic study.

Malignant transformation of the lesion is rare but when present often involves the joint cavity. Cysts are present in about 20% of the cases & both MRI & CT can define fluid levels.

Differential Diagnosis -

1.Giant cell tumour which is seen in mature skeleton & always begins at the metaphysial ends of the long bone adjacent to the ossified epiphyseal line. It is usually subarticular in location & has soap bubble appearance.

2. Enchondroma has predilection for the short tubular bones (50 %). Long bones are less commonly involved. The lesion is geographic, expansile osteolytic lesion in the metaphysis of the long bone. It has popcorn like / annular calcifications with a lobulated growth pattern with frequent scalloping of the endosteal cortex

3. Chondromyxoid fibroma has also eccentrically located radiolucent lesion with scalloped margins often eroding / ballooning the cortex. It has predilection for lower extremity bones

4. Aneursymal bone cyst is seen in childres & adolescents below 20 years of age. It is eccentric in location with a buttress of periosteum.