Practice Essentials
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]
Although the exact etiology of chondroblastoma remains uncertain, the presentation, appropriate evaluation, and treatment of patients with the condition have been well described. (See Presentation, Workup, and Treatment.) Surgical treatment is generally indicated. Percutaneous radiofrequency ablation (RFA) may be an alternative to surgery for the treatment of certain chondroblastomas.
Pathophysiology
Various theories have been proposed concerning the pathogenesis of chondroblastomas. Mii et al described the results of ultrastructural examination of chondroblastomas, [3] demonstrating subcellular calcium-containing precipitates similar to those seen in chondrocytes. On the basis of these findings, the authors concluded that the tumors are of chondrogenic origin.
Aigner et al, however, noted the presence of osteoid matrix–containing type I collagen and the absence of true cartilage matrix production. [4] They considered the term chondroblastoma to be a misnomer and believed that the tumor should be reclassified as a bone-forming neoplasm.
Brien et al 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). [5] 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.
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. [6]
Etiology
Risk factors for chondroblastoma remain to be fully defined. There have been reports of abnormalities in chromosomes 5 and 8, as well as of p53 mutations, in patients with chondroblastoma. [7] Sjögren et al performed cytogenetic analysis of benign and malignant cartilage tumors, and although no consistent karyotypic abnormalities were oberved, there were recurrent breakpoints seen at 2q35, 3q21-23, and 18q21. [8]
Epidemiology
In the United States, chondroblastoma accounts for approximately 1% of all bone tumors. The international incidence is not reported in the current literature.
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.
The male-to-female ratio has been 2:1 in most series. No racial predilection has been recognized.
Prognosis
Patients with benign chondroblastoma may limit activities because of pain. Malignant chondroblastomas, which may occur many years after the original lesion (even in the absence of radiation), are extremely rare—so rare that chondroblastomas have been reclassified from "rarely metastasizing" to "benign" by the World Health Organization [9] (WHO)—and are associated with a dismal prognosis.
Local recurrence in long-bone lesions is approximately 10% and is higher for chondroblastomas arising in flat bones, especially those lesions arising in the vicinity of the triradiate cartilage. Average time to recurrence is 34 months after initial treatment. Most authors have not reported any significant difference in recurrence rates for tumors, regardless of the age or sex of the patient, the size of the lesion, the amount of calcification or vascular invasion seen on histologic examination, the duration of follow-up, or the method of treatment.
Springfield attributed a higher recurrence rate in patients with open physeal plates to a less aggressive curettage performed in an effort to avoid future growth arrest. [10] Recurrences may be treated with repeat curettage, with or without bone graft or cementation, and with marginal excision of any soft-tissue component. [11]
Whereas most chondroblastomas are small, well-marginated lesions that are successfully treated with intralesional curettage, a small subset of chondroblastomas behave in a much more aggressive fashion. Some of these tumors retain their benign microscopic features but nonetheless become very large or have the capability of metastasizing to the lungs and soft tissues.
Metastases may be synchronous or metachronous, occurring concurrently with the primary bone tumor or up to 33 years later. Metastases can occur even without surgical manipulation or local recurrence of the primary tumor. These more aggressive lesions may be treated with en-bloc resection and reconstruction where intralesional curettage would leave a large, bony defect. Pulmonary implants or soft-tissue metastases should be resected, especially if they are progressive.
Another rare subset of chondroblastomas may become frankly malignant even though no prior radiation therapy was used. Kyriakos et al used the term malignant chondroblastoma to describe tumors that continue to grow or disseminate, not just those that metastasize. [12] Malignant transformation typically occurs many (usually >10) years after treatment of the initial benign lesion. Pulmonary metastases may develop along with the malignant bony lesion.
Microscopic examination of the malignant bone lesion shows features similar to the original lesion (along with other areas with nuclear pleomorphism), abundant and abnormal mitotic figures, tumor necrosis, and intravascular thrombi. Ostrowski et al reported a patient with malignant transformation of a recurrent pelvic chondroblastoma with a p53 mutation. [13] Frankly malignant chondroblastoma tends to be resistant to surgery, radiation, and chemotherapy, and patients with these tumors have had dismal prognoses.
A retrospective study by Farfalli et al focused primarily on long-term joint status and functional outcomes (rather than oncologic outcomes) after curettage for epiphyseal chondroblastoma. [14] The investigators found that aggressive curettage of epiphyseal chondroblastoma frequently led to osteoarthritis and that tumors in the proximal femur appeared particularly likely to be associated with secondary osteoarthritis and prosthetic replacement.
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Radiograph of epiphyseal lesion (hip).
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Radiograph demonstrating tumor on both sides of physis (humerus).
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Bone scan.
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Magnetic resonance image of a hip showing lobular pattern of chondroblastoma.
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Histology of chondroblastoma.
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Chondroblastoma histology demonstrating chicken-wire calcifications.
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Axial computed tomography scan of the pelvis demonstrates a lesion of the femoral head without noticeable internal matrix production. The epiphyseal location of the lesion is a clue to the correct diagnosis.
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Plain film of the hip shows a femoral head with a lytic lesion with surrounding sclerosis in the epiphysis of the proximal femur. Internal matrix formation is not present, but that finding can be a feature of this tumor.
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Coronal T1-weighted sequence shows a lesion of the epiphysis with medium signal intensity. Small islands of matrix are noted.
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Low-power photomicrograph demonstrates islands of hyaline-type cartilage, which can often be seen in chondroblastomas.
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Medium-power photomicrograph with lobules of chondroid matrix. In these lesions, the cartilage can be eosinophilic, with superficial resemblance to osseous matrix. Correlation with the radiologic studies is often helpful when in doubt.
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Medium-power photomicrograph demonstrates secondary cystic changes, which can often accompany chondroblastomas. Careful sampling of the tumor will show the correct etiology for the changes noted here.
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Giant cells are a component of this tumor, and in areas that are rich in giant cells, sampling will show the chondroblastomatous portions of the tumor.
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Immunohistochemistry for S100 is positive in chondroblastomas and is often helpful, especially when the tissue sample is small.
