Chondroblastoma

Tumor biology and incidence

Benign giant cell and chondroid-type lesion
Rare, aggressive tumor of bone composed of immature chondroblasts and scant chondroid matrix
Predilection for epiphyses of long bones prior to epiphyseal closure
Arise in secondary centers of ossification
Approximately 5% of benign bone tumors

Age

Adolescents most commonly affected
95% of cases ranges from 5 to 25 years old

Gender

Male:Female = 3:2

Presentation

Pain in joint adjacent to tumor without history of trauma
Swelling
Pain often present for months or years; frequently misdiagnosed as chronic synovitis

Physical findings

Joint effusion
Decreased range of motion
Swelling
Tenderness to palpation

Plain films

Well-defined round or oval lytic lesions
Radiolucent
Scalloping or expansion of the cortex not uncommon
Punctate or ring calcifications may be present

Site

Most commonly epiphyseal: femur > humerus > tibia > pelvis > tarsal bones

Size

Variable; typically ranges from 1 to 6 cm

Tumor effect on bone

Lytic lesion with a well defined (geographic) margin
Bulging of overlying cortex can occur due to metaphyseal extension

Bone response to tumor

Sclerotic rim of reacitve bone, which can become thicker with time
May have a metaphyseal periosteal reaction distal to lesion

Matrix

Lytic, with possible internal cartilagenous calcifications

Cortex

May be expanded with metaphyseal lesion

Soft tissue mass

None

Bone scan

Increased uptake of chondroblastomas on bone scan may be related to tumor hyperemia

CT scan

Excellent for visualizing internal calcification
Can depict matrix mineralization, soft-tissue extension, and cortical erosion, if present.
Coronal and sagittal reconstructions may be helpful in evaluating extension across physeal plate

MRI

Typical bright T2-weighted, lobulated chondroid matrix
May have variable surrounding medullary edema and periosteal reaction; may be misleading in defining extent of lesion

Differential diagnosis

Giant cell tumor (no calcifications, ossification, or sclerotic margin)
Clear cell chondrosarcoma
Chondromyxoid fibroma
Enchondroma
Osteomyelitis
Hemangioma
Fibrous dysplasia and nonossifying fibroma (rare to affect epiphysis)
Degenerative joint cyst

Natural history

Small and slow-growing; generally do not resolve without surgical management
Chondroblatoma of the pelvis is usually more aggressive than lesions in long bones
Most patients are close to skeletal maturity; residual deformity after treatment is minimal
Patient less than 10 years of age, take care not to damage growth plate
Synchronous and metachronous metastases are very rare, but have been reported

Pathology

Gross: grey tan tissue; chondroid component not usually seen
Microscopic: proliferating chondroblasts (mononuclear cells); round to oval in shape with well-defined cell margins\
- Variable amounts of chondroid, which stains pink rather than having a typical bluish appearance, are present
- Chicken wire calcification may occur
- Numerous giant cells may be present; differentiation from giant cell tumor can be difficult

Diagnosis and treatment

Lesion must be well visualized at resection; open joint if required
Curettage is treatment of choice; must be thorough
Phenol and liquid nitrogen generally not used for fear of growth plate or articular cartilage damage
Defect packed with autograft or allograft
Recurrence rate from 10% to 30%

Complications

Complications related to surgical treatment
- Infection
- Premature physeal closure
- Failure of allograft
- Development of degenerative joint changes
Pathologic fracture through lesion (rare)
Premature physeal closure, subsequent limb-length discrepency or angular deformity (rare)
Malignant transformation (very rare)