Tumor biology and incidence

Chondroblastoma is a rare, aggressive tumor of bone composed of immature chondroblasts and a scant chondroid matrix. The cell of origin is thought to arise from the epiphyseal plate or some remnant of it. Chondroblastoma is an epiphyseal lesion found primarily in long bones of adolescents.  It represents 1% of all bone tumors.

Age

The mean age at presentation of chondroblastoma is 20 years old. Ninety percent of cases occur in 5 to 25 year olds. 

Gender

Male:Female = 2-3:1

Presentation

Chondroblastomas typically present as pain near a joint without a history of trauma.  Pathologic fracture is rare, but patients may develop a secondary synovitis. Usually constitutional symptoms are absent.

Physical findings

Decreased range of motion, swelling, tenderness to palpation at the nearby joint is common.  Effusion may be present (approximately 30%).

Plain films

Chondroblastomas are well-defined lytic lesions.  Scalloping or expansion of the cortex is not uncommon.  Consistent with it's chondroid nature, punctate or ring calcifications may be present.

Site
Chondroblastomas are found in the epiphysis of long bones.  They are more often found in the lower extremity with the distal femur being the most common site.  They are also commonly found in the proximal tibia, proximal humerus, and distal tibia.

Size

The size is variable but typically ranges from 1-6cm.

Tumor effect on bone

Chondroblastomas may cause expansion or scalloping of the cortex. 

Bone response to tumor

A sclerotic rim of reacitve bone is generally present.

Matrix

Primarily lytic, with punctate calcifications sometimes present.

Cortex

Scalloping or expansion of the cortex is not uncommon.

Soft tissue mass

None

Bone scan

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

CT Scan

CT scans can depict matrix mineralization, soft-tissue extension, and cortical erosion, if present.  Coronal and sagittal reconstructions may be helpful in evaluating extension across the physeal plate.

MRI

Chondroblastomas typically demonstrate low signal intensity on T1-weighted images and high or variable intensity on T2-weighted images.  Variable signal intensity is related to abundant immature chondroid matrix, chondroblastic hypercellularity, calcification, and hemosiderin deposition.  Adjacent inflammatory changes leading to high signal intensity within the meduallary canal may be misleading in defining the extent of the lesion. 

Differential Diagnosis

Giant cell tumor (generally older, do NOT have calcifications)

Clear cell chondrosarcoma

Chondromyxoid fibroma

Enchondroma

Osteomyelitis

Hemangioma

Fibrous dysplasia and nonossifying fibroma (RARE to affect epiphysis)

Natural history

Most chondroblastomas are small and slow-growing.  They generally do not resolve and therefore surgical management is recommended.  A small subset of chondroblastomas, more common in pelvic lesions, behave in a more aggressive fashion.  Synchronous and metachronous metastases are very rare, but have been reported.

Pathology

Grossly, the tumor appears as lobulated, grayish-pink soft tissue with blue chondroid tissue (rarely seen) and calcifications.  Histologically, the lesion is composed of chondroblasts, multinucleated giant cells, and foci of chondroid and occaisionally hyaline matrix. The classic description is that of "chicken-wire calcification" which occurs as the matrix surrounding the tumor cells begins to calcify.

Diagnosis and treatment

As stated above, managment is typically surgical as there is little evidence to suggest that chondroblastomas spontaneously resolve.  The most common treatment is curettage and autograft or allograft bone grafting.  Polymethalmethacrylate is occasionally used for large lesions needing more structural support.  The rare, more aggressive lesions may be treated with en bloc resection and reconstruction when intralesional curettage would leave a large bony defect. 

Complications

Local recurrance rates are reported around 10%.  Pathologic fracture through the lesion is rare.  Premature physeal closure and subsequent limb-length discrepency or angular deformity is rare.  Complications related to surgical treatment includes infection, premature physeal closure, failure of allograft, and development of degenerative joint changes.  Malignant transformation is very rare.

Recommended Reading

Suneja R, Grimer RJ, Belthur M, Jeys L, Carter SR, Tillman RM, Davies AM. Chondroblastoma of bone: long-term results and functional outcome after intralesional curettage.J Bone Joint Surg Br. 2005 Jul;87(7):974-8.

Ramappa AJ, Lee FY, Tang P, Carlson JR, Gebhardt MC, Mankin HJ. Chondroblastoma of bone. J Bone Joint Surg Am. 2000 Aug;82-A(8):1140-5.

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