Chondroblastoma is a benign primary bone tumor with cartilaginous differentiation usually involving ends of long bones and is characteristically epiphyseal tumor
Incidence – less than 2% of all bone tumors & 5% of benign tumors
Clinical features – Patient presents with mild localised pain with duration of few weeks to years and with tender swelling over involved bone
Age – mostly second decade (but can occur from 2 to 83 years)
Sex – male predominance
Sites–
long tubular bones(60%), usually femur (distal epiphysis), proximal humerus and proximal tibia
Other regions are ilium ( from the region of triradiate cartilage, temporal bone, calcaneous and talus together
Size – Usually less than 5cms
X-ray findings:
Typical lucent defect at the end of a long bone mainly involving medulla
Some of the tumors may arise in cortex or rarely on the surface of bone
Tumors appears as round or oval lucency located eccentrically or in the middle of epiphysis
Lucency has epicentre in epiphysis and extend across the epiphyseal plate to involve metaphysis is characteristic of chondroblastoma
Scletotic rim is present in 50% of tumors
10% of tumors show periosteal new bone formation
Presence of secondary aneurysmal bone cyst suggest an aggressive neoplasm
CT scan is helpful to know extent of joint involvement
MRI shows peritumoral oedema and defines better periosteal new bone formation
Gross:
On curettage, chondroblastomas are soft pink to gray tumors with chalky white foci of calcification
Cysts and areas of haemorrhages may be present
On excision tumor appears well circumscribed lobulated with cystic areas
Microscopic findings:
Tumor consists of giant cells and mononuclear cells
Mononuclear cells have oval elongated nucleus with evenly distributed chromatin and longitudinal groove giving “ coffee bean” appearance
Nucleoli are not prominent
Multinucleated giant cells may be present which may range from few to large number
Cartilagenous matrix formed by tumor may be focal or abundant which stains pink rather than blue
Chondroblastomas may contain calcification which has lace like arrangement between the individual tumor cell (chicken wire like calcifications)
Mononuclear cells may have vesicular nuclei and abundant pink cytoplasm resembling epithelioid cells are seen in chondroblastomas of skull
Some of cells may have brown granular pigment in the cytoplasm
Few tumors may have mononucleated cells which are spindle shaped and have hemangiopericytomatous vascular pattern
Secondary aneurysmal bone cyst is found in more than 1/3rd of chondroblastomas
IHC – Mononuclear cells in tumor stain for S-100 positive
Differential diagnosis:
Differential diagnosis includes
Giant cell tumor
Chondomyxoid fibroma
Osteosarcoma
Giant cell tumor:
Do not show reactive sclerosis at periphery as chondroblastomas
Mononuclear cells lack nuclear grooving
They lack chondroid matrix and calcification which are seen in chondroblastoma
Chondromyxoid fibroma:
Involves metaphysis in contrast to chondroblastoma which involve epiphysis
It also has lobulated growth pattern and myxoid background
Mononuclear cells also has similar features as chondroblastoma
It is distinguished on the basis of location
Osteosarcoma
Cells are arranged in sheets and infiltrate bony trabeculae
Treatment :
Curettage is the treatment of choice
Recurrence can occur in 6 to 15% of cases
Benign pulmonary metastasis occur with chondroblastoma
Reference
K.Krishnan Unni,Carrie Y. Inwards, Julia A.Bridge, Lars-Gunnar Kindblom, Lester E. Wold. Chondroblastoma. In:Cartilagenous lesions: Tumors of the Bones and joints. AFIP Atlas of tumor pathology. Series 4.61-66.