Background
A chondroblastoma is a rare, usually benign, tumor of bone that accounts for approximately 1% of all bone tumors. In 1931, Codman classified it as a chondromatous variant of giant cell tumors, when he described these lesions in the proximal humerus.[1] A decade later, Jaffe and Lichtenstein renamed the Codman tumor a benign chondroblastoma to emphasize the chondroblastic genesis of the lesion and to distinguish it from the classic giant cell tumor of bone.[2]
Examples of chondroblastoma lesions are shown below.
Radiograph of epiphyseal lesion (hip). 
Radiograph demonstrating tumor on both sides of physis (humerus). 
Magnetic resonance image of a hip showing lobular pattern of chondroblastoma. Recent studies
In a study by Rybak et al of 17 patients who were treated with radiofrequency ablation for chondroblastomas, all patients reported relief the day after the procedure. Of 14 patients available for follow-up, 12 reported complete relief of symptoms without the need for medications, and all returned to previous activities. One patient, who had the largest lesion, required surgery because of articular collapse in the area of treatment. Another patient required surgical treatment because of mechanical problems. The authors concluded that percutaneous radiofrequency ablation is an alternative to surgery for selected chondroblastomas but that larger lesions under weight-bearing surfaces need to be approached with caution because of an increased risk of articular collapse and recurrence.[3]
Sailhan et al studied 87 cases of chondroblastoma in children and found that epiphyseal chondroblastomas were associated with a higher risk of recurrence than were metaphyseal, apophyseal, and epiphyseal-metaphyseal lesions. In 63% of the patients, treatment consisted of intralesional curettage with autogenous bone grafting; functional outcome was good for 68.5% of the patients; and 32% of the lesions recurred.[4]
Pathophysiology
Various theories have been proposed concerning the origin of chondroblastomas. Mii and colleagues described the results of ultrastructural examination of chondroblastomas.[5] Their studies showed subcellular, calcium-containing precipitates that are similar to those seen in chondrocytes. Based on these findings, the authors concluded that the tumors are of chondrogenic origin. Aigner and colleagues, however, noted the presence of osteoid matrix–containing type I collagen and the absence of true cartilage matrix production.[6] They considered the term chondroblastoma to be a misnomer and believed that the tumor should be reclassified as a bone-forming neoplasm.
Brien and colleagues compared the characteristics of chondroblastoma of bone to chondroblastoma of soft tissue, giant cell tumor of the tendon sheath (GCTTS), and pigmented villonodular synovitis (PVNS).[7] On examination of about 15 examples of GCTTS and PVNS, large areas of chondroid differentiation were noted that could not be distinguished from chondroblastoma of bone by either histologic or electron microscopic features. The researchers theorized that chondroblastoma of bone stems from an intraosseous proliferation of tendon sheath cells that have a predilection for chondroid formation. While the exact etiology of chondroblastoma remains uncertain, the presentation, appropriate evaluation, and treatment of patients with the condition have been well described.
Chondroblastomas typically occur in the epiphyses of tubular long bones. The distal femoral and proximal tibial epiphyses are most frequently involved, followed by the proximal humerus, where approximately 18% of chondroblastomas appear.[4]
Epidemiology
Frequency
United States
Chondroblastoma accounts for approximately 1% of all bone tumors.
International
International incidence is not reported in current literature.
Mortality/Morbidity
Patients with benign chondroblastoma may limit activities due to pain. Malignant chondroblastomas, which may occur many years after the original lesion (even in the absence of radiation), are extremely rare and are associated with a dismal prognosis.
Race
No racial predilection is recognized.
Sex
The male-to-female ratio is 2:1 in most series.
Age
Approximately 92% of patients presenting with chondroblastoma are younger than 30 years. However, chondroblastomas have been reported to arise in patients as young as 2 years and as old as 83 years. In several large series, most patients were diagnosed in the second decade of life.
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