Practice Essentials
Osteosarcoma of bone is a high-grade tumor with a long-term survival rate of 60-85%. Several variants of osteosarcoma exist. [1, 2] High-grade variants include telangiectatic osteosarcoma, small-cell osteosarcoma, high-grade surface osteosarcoma, and secondary osteosarcoma. Other variants (eg, low-grade central osteosarcoma, parosteal osteosarcoma, and periosteal osteosarcoma) are less aggressive entities with a lower rate of metastasis and a long-term survival rate approaching 90%.
Low-grade central osteosarcoma is a rare variant of osteosarcoma that originates within the medullary cavity of bone and is often mistaken for fibrous dysplasia. [3] At histologic examination, it appears as a Broders grade 1 or grade 2 lesion.
The Broders grading system was designed to determine the grade of malignancy of a given tumor on the basis of histologic features. [4] These characteristics include the following:
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Degree of cellularity
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Cellular pleomorphism or anaplasia
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Mitotic activity
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Necrosis
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Expansive or infiltrative growth
Initial diagnosis of osteosarcoma is often difficult. [5, 6] Frequently, it is diagnosed only after a recurrence of disease in an area of bone where a diagnosis of fibrous dysplasia had previously been made. [7] Osteosarcoma has also been mistaken for other benign and malignant bone conditions, including nonossifying fibroma, well-differentiated fibrosarcoma, aneurysmal bone cyst, osteoblastoma, and desmoplastic fibroma. [8, 9, 10] Its rarity likely contributes to these inaccurate diagnoses.
To the author's knowledge, the largest series in the literature to date is that of Kurt et al, which was published in 1990 and included 80 cases. [11] Low-grade central osteosarcoma has a better prognosis than high-grade osteosarcoma does. (See also Aneurysmal Bone Cyst Imaging and Osteoblastoma Imaging.)
The presence of a low-grade central osteosarcoma is an indication for treatment. (See Treatment.) The only contraindication would be the presence of widespread metastases, for which palliative treatment may then be indicated. The use of radiation therapy or chemotherapy has been controversial. Wide excision, possibly including amputation, is the treatment of choice.
Anatomy
Low-grade central osteosarcoma may occur in long bones (82.25%), [12] flat bones (13.75%), or the hands and feet (4%).
Sites in specific long bones are as follows:
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Distal femur - 41%
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Proximal tibia - 12.5%
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Distal tibia - 8.75%
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Fibula - 5%
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Radius - 5%
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Proximal femur - 3.75%
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Midshaft femur - 2.5%
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Humerus - 2.5%
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Ulna - 1.25%
Sites in specific flat bones are as follows:
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Ribs - 3.75%
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Mandible - 2.5%
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Maxilla, clavicle, occipital bone, scapula, vertebra, and ilium - 1.25% each
Pathophysiology
Low-grade central osteosarcomas typically develop de novo in the long bones of patients aged 20-30 years. Patients typically seek treatment when symptoms, which usually involve pain only at the site of the tumor, persist. The tumor grows locally within the bone of origin. Approximately 25-55% of these tumors invade the surrounding adjacent soft tissue. If the tumor is not adequately resected early in its course, pulmonary metastasis may develop as a late complication.
Etiology
The exact etiology of low-grade central osteosarcoma is unknown. Osteosarcomas have been experimentally induced in animals by a variety of means, including irradiation, [13] inoculation with Moloney sarcoma virus, [14] injection of bone-seeking radionucleotides, [15] and inhalation of aerosolized plutonium 238 dioxide. [16] Many of these induced tumors are well-differentiated osteosarcomas, including low-grade central osteosarcomas.
Epidemiology
In the study by Kurt et al, low-grade central osteosarcoma accounted for 1.2-1.9% of all cases of osteosarcoma. [11] Internationally, low-grade central osteosarcoma has accounted for 0.7% of all cases of osteosarcoma, as reported by the Instituto de Rizzoli at the University of Bologna, Italy.
The mean patient age at presentation is 28.3 years. Patients with low-grade central osteosarcoma are approximately 1 decade older than patients with traditional osteosarcoma, though cases have been reported in patients aged 9-83 years. The male-to-female ratio is 1:1; this is unlike traditional osteosarcoma, which has a male-to-female ratio of 1.4:1.
Prognosis
Recurrences rates for of low-grade central osteosarcoma are as follows:
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Recurrence rate after wide excision - Less than 5%
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Recurrence rate after intralesional curettage or marginal excision - 80-100%
Survival rates for patients with the disease are as follows:
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Five-year disease-free survival rate - 90%
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Ten-year disease-free survival rate - 85%
Of tumors that recur, 15% recur as high-grade osteosarcomas with prognoses similar to those associated with traditional osteosarcomas. Recurrences can be observed 6 months to 20 years after primary treatment.
Pulmonary metastases are rare, but they can occur 5-10 years after successful surgical excision of the primary tumor. Metastases are more common in recurrences, especially when the lesions recur as high-grade osteosarcomas.
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Standard radiographs of a low-grade central osteosarcoma of the distal femur.
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Magnetic resonance image (MRI) of low-grade central osteosarcoma of the distal femur.
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Magnetic resonance image (MRI) of low-grade central osteosarcoma of the distal femur.
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Magnetic resonance image (MRI) of low-grade central osteosarcoma of the distal femur.
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Bone scan of a low-grade central osteosarcoma of the distal femur.
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Photomicrograph of a low-grade central osteosarcoma (original magnification, X40). Courtesy of Dr Ronald Burns, Palmetto Richland Department of Pathology.
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Photomicrograph of a low-grade central osteosarcoma (original magnification, X100). Courtesy of Dr Ronald Burns, Palmetto Richland Department of Pathology.
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Photomicrograph of a low-grade central osteosarcoma (original magnification, X400). Courtesy of Dr Ronald Burns, Palmetto Richland Department of Pathology.
