eMedicine Specialties > Radiology > Musculoskeletal

Osteosarcoma, Variants

Geoff Hide, MBBS, MRCP, FRCR, Consultant Musculoskeletal Radiologist, Department of Radiology, Freeman Hospital; Honorary Clinical Lecturer, Faculty of Medical Sciences, University of Newcastle upon Tyne

Updated: May 21, 2007

Introduction

Background

Osteosarcoma is the most common primary malignant tumor of bone, excluding plasma cell myeloma. Approximately 75% of all osteosarcomas are of the classic or conventional type, and the remaining 25% comprise the osteosarcoma variants, which are the subject of this article.¹ The variants are a heterogeneous group of osteosarcomas with a range of different imaging and behavioral features.

Pathophysiology

Osteosarcoma is a malignant mesenchymal sarcoma characterized by the direct formation of bone or osteoid by tumor cells. For further information on the individual pathologic characteristics of the osteosarcoma variants, the reader is directed to the References section.

Frequency

United States

The peak incidence of osteosarcoma occurs in the second decade of life, which corresponds to the maximal period of skeletal growth. The incidence of osteosarcoma in persons younger than 20 years is 4.8 cases per million population. Approximately 75% of these cases are conventional osteosarcomas. Frequency data for the individual osteosarcoma variants is difficult to calculate because many are rare tumors. The table below shows the relative percentages of the osteosarcoma variants.^1,2

Frequency of osteosarcoma variants in the United States

Mortality/Morbidity

The overall prognosis for patients with osteosarcoma depends on the stage of the tumor at presentation. Without metastases, long-term survival is in the order of 60-85%.

• Telangiectatic osteosarcoma has been considered more aggressive than classic osteosarcoma, but studies of long-term survival after optimum treatment now indicate that the aggressiveness of telangiectatic osteosarcoma is similar to that of the classic type.
• Intraosseous low-grade osteosarcoma generally has a good prognosis.
• Gnathic osteosarcoma is less frequently associated with metastatic spread than is conventional osteosarcoma, but local disease recurrence is often problematic.
• The prognosis for intracortical osteosarcoma is unclear because of its rarity.
• Both small-cell and secondary osteosarcoma are generally associated with a poor prognosis.
• High-grade surface osteosarcoma has a prognosis similar to that for a conventional osteosarcoma.
• The prognosis for periosteal osteosarcoma is better than that for conventional osteosarcoma.
• The prognosis for a parosteal osteosarcoma is generally excellent.
• The prognosis for multicentric osteosarcoma is dire.

Race

Osteosarcoma occurs in all racial and ethnic groups, but its frequency is slightly greater in African Americans than in Caucasians.

Sex

Most variants have a sex distribution similar to that of conventional osteosarcoma. That is, they are slightly more common in males than in females. Gnathic osteosarcoma and intraosseous low-grade osteosarcoma are believed to show a more equal sex distribution, and some studies of parosteal osteosarcoma have suggested that the tumor is more prevalent in females.

Age

Conventional osteosarcoma has a wide age range, with a peak in the second decade. This peak is thought to be associated with the period of maximal intensity of skeletal growth.

• Most of the osteosarcoma variants show a similar age distribution, with the exception of intraosseous low-grade, gnathic, and parosteal osteosarcomas. These have a peak slightly later, in the third decade of life.
• A second, smaller peak in the distribution of osteosarcoma as a whole is seen in late adulthood. This second peak is principally due to the occurrence of secondary osteosarcoma at this stage of life.

Anatomy

Conventional osteosarcoma is most frequent in areas of high skeletal growth, especially the metaphyseal regions of the distal femur, proximal tibia, and proximal humerus. Most osteosarcoma variants follow a similar distribution, with the exception of gnathic (mandible and maxilla) lesions, intracortical lesions (rare but more typically diaphyseal), periosteal lesions (more typically diaphyseal), and secondary osteosarcomas. The last osteosarcomas frequently occur in the pelvis and proximal femur, often in association with Paget disease.

Presentation

Most osteosarcoma variants have presentations similar to that of a conventional osteosarcoma, with pain, swelling, and a palpable mass that may have been present for weeks or months. Parosteal osteosarcoma is notable for the presence of a mass that in some cases may have been present for years. Intraosseous low-grade tumors may have a presentation that is similarly prolonged.

Multicentric osteosarcoma may result from 1 of 2 processes. Multiple primary tumors may occur either synchronously or asynchronously. Alternatively, multicentric disease may occur from a single primary lesion with metastases to other skeletal sites at presentation. Regardless of controversies over which mechanism is more likely, when multicentric disease is initially present, the prognosis is poor.

Preferred Examination

Preferred modalities for evaluating primary disease are radiography, magnetic resonance imaging (MRI), and sometimes computed tomography (CT) scanning. Staging is always performed by using chest CT scanning to detect pulmonary metastases. Isotopic bone scanning is generally used to detect skeletal metastases or synchronous tumors, but whole-body MRI may replace this study.

Differential Diagnoses

Other Problems to Be Considered

Osteochondroma (parosteal osteosarcoma)
Myositis ossificans (parosteal osteosarcoma)
Aneurysmal bone cyst (telangiectatic osteosarcoma)
Fibrosarcoma

Differential diagnoses

Ewing and primitive neuroectodermal tumor
Langerhans cell histiocytosis
Infection
Rhabdomyosarcoma

Radiography

Findings

Telangiectatic osteosarcoma is generally lytic, with a periosteal reaction and soft-tissue mass. When the tumor margins are well defined, it may mimic an aneurysmal bone cyst. Small-cell osteosarcoma appears similar to a conventional osteosarcoma; it often has mixed areas of sclerosis and lysis. Intraosseous low-grade osteosarcoma may be lytic, sclerotic, or mixed; it often has deceptively benign features of well-defined margins and the absence of periosteal changes or a soft-tissue mass.

Gnathic tumors may be lytic, sclerotic, or mixed, and bone destruction, periosteal reaction, and soft-tissue extension are common. Intracortical osteosarcomas are described as radiolucent and geographic, and they contain a small amount of internal mineralization. High-grade surface osteosarcomas are shown as broad-based soft-tissue masses with varying degrees of mineralization arising from the surface of the bone.

Parosteal osteosarcomas are typically densely ossified tumors arising from a broad base on the adjacent bone. Unlike osteochondromas, parosteal osteosarcomas involve no continuation of the medullary cavity into the tumor.

Computed Tomography

Findings

CT scanning is helpful in the evaluation of a variety of the osteosarcoma variants. It may demonstrate fluid levels in telangiectatic osteosarcoma, and a contrast-enhanced CT scan can be helpful in discriminating such a lesion from an aneurysmal bone cyst. Telangiectatic osteosarcoma differs from an aneurysmal bone cyst in that the former has a rim of tumor cells that surrounds the cystic spaces. This tissue rim shows typically nodular enhancement after the intravenous administration of contrast material.

CT scanning is useful in the evaluation of bone changes occurring in areas of complex anatomy. Examples are the changes in the maxilla or mandible that are associated with gnathic osteosarcoma and those in the pelvis that are associated with secondary osteosarcoma. CT scanning provides useful information about the surface osteosarcoma variants, including parosteal, periosteal, and surface high-grade tumors.

When appropriate and performed in consultation with an orthopedic oncologist, CT scanning can be useful in guiding biopsy.

Magnetic Resonance Imaging

Findings

MRI is the optimum technique for local staging of osteosarcomas. In certain cases, MRI is combined with CT scanning. MRI accurately demonstrates the extent of a tumor within bone and soft tissue.

At least 1 sequence, either a T1-weighted or a short-tau inversion recovery (STIR) sequence, should be performed to image the entire bone. This is necessary to exclude skip lesions that are present within the same bone but are distant from the primary lesion. Periosteal osteosarcoma is typically a chondroblastic lesion, and the tumor usually has high signal intensity on T2-weighted MRIs.

Degree of Confidence

MRI is more sensitive than CT scanning in demonstrating fluid-fluid levels in telangiectatic osteosarcoma because of its greater intrinsic soft-tissue contrast.

False Positives/Negatives

Fluid-fluid levels can be seen in benign bone lesions as well, particularly aneurysmal bone cysts.

Ultrasonography

Findings

Ultrasonography can demonstrate the soft-tissue extent of the tumor, but it cannot be used to evaluate the intramedullary component of the lesion. Ultrasonography is not routinely used in staging such lesions. Sonography can be useful in guiding percutaneous biopsy of the soft-tissue component of the tumor, again in consultation with an orthopedic oncologist.

Nuclear Imaging

Findings

Osteosarcomas typically show increased uptake of radioisotope; this characteristic makes bone scans sensitive but not specific. Bone scans are most useful in excluding multifocal disease. Multiple-gated acquisition (MUGA) cardiac scans may be required to monitor the toxic effects of certain chemotherapeutic agents.

Angiography

Findings

Angiography is no longer used in the staging of osteosarcoma.

Intervention

Histologic confirmation of the nature of the tumor is initially required; the analysis should be performed after MRI and in consultation with the tumor surgeon. Biopsy must be performed after the MRI study because hemorrhage occurring at the time of biopsy alters the signal intensity characteristics of the tumor at subsequent MRI examinations. The site of the biopsy track must be planned to prevent contaminating the muscle compartments that the surgeon would not otherwise excise. The biopsy track is removed during surgery, and consideration should be given to marking the track with suture material or dye if there will be a delay between biopsy and formal excision.

Tumors are often densely sclerotic and difficult to examine with percutaneous biopsy, but the associated soft-tissue component is often amenable to sonography-guided biopsy.

Treatment is geared around surgery, with limb salvage when possible. Presurgical chemotherapy is used. The response to chemotherapy is assessed in the resected specimen or by means of pre-resection biopsy. The response is considered good when tumor necrosis is greater than 90%. This necrosis is a predictor of a successful outcome.

Multimedia

Media file 1: Frontal radiograph of the distal femur in a patient with telangiectatic osteosarcoma. The radiograph shows mixed medullary sclerosis and lucency, cortical destruction medially, aggressive periosteal changes, and a large soft-tissue mass with peripheral ossification.

Media file 2: Coronal short-tau inversion recovery (STIR) magnetic resonance imaging (MRI) scan of the same patient as in Image 1. Note the abnormal signal intensity of the bone marrow in the metaphysis of the femur, the cortical destruction, and the prominent soft-tissue mass with the surrounding edema or reactive zone.

Media file 3: Axial T2-weighted magnetic resonance imaging (MRI) scan of the same patient as in Images 1-2. A fluid-fluid level is present within the abnormal extraosseous tumor mass (arrow). The abnormal intramedullary tissue is less obvious in this sequence than in others.

Media file 4: Lateral radiograph of the proximal tibia in a patient with parosteal osteosarcoma. Note the opaque, lobulated, amorphous or cloudlike mass of abnormal, ossified tumor, which is inseparable from the posterior aspect of the tibia.

Media file 5: Axial computed tomography (CT) scan of the same patient as in Image 4. The ossified tumor mass is readily shown, and the thickened cortex is visible at the junction of tumor and normal bone (arrow). The medullary cavity of the tibia appears normal.

Media file 6: Axial T1-weighted magnetic resonance imaging (MRI) scan of the same patient as in Images 4-5. The medullary cavity of the tibia shows predominantly normal signal intensity, except posteriorly, where the slightly reduced signal intensity raises the possibility of early tumoral invasion (arrow). This area was normal on histologic examination.

Media file 7: Anteroposterior (AP) radiograph of the proximal tibia in a child with periosteal osteosarcoma. The metal pointer localizes the lesion for biopsy.

Media file 8: Coronal short-tau inversion recovery (STIR) magnetic resonance imaging (MRI) scan of the same patient as in Image 7. The ossified component of the tumor shows low signal intensity (white arrow), but superficially, hyperintense material (black arrow) is present. This may be chondroblastic soft-tissue extension of tumor, adjacent reactive edema, or a combination of both.

Media file 9: Frontal radiograph of the mandible in an adult with gnathic osteosarcoma. The radiograph shows a large, expansile lesion in the right ramus (arrow), with a mixed lytic and sclerotic appearance.

Media file 10: Axial computed tomography (CT) scan obtained with bone window settings, in the same patient as in Image 9. Osseous expansion and the mixed lytic and sclerotic process are again appreciated. A large soft-tissue component (arrow) also is now visible.

Media file 11: Axial computed tomography (CT) scan obtained with soft-tissue window settings, in the same patient as in Images 9-10. Extension of ossified matrix into the soft-tissue component of the tumor is shown (arrow).

Media file 12: Anteroposterior (AP) radiograph of the proximal femur in a patient with Paget disease demonstrates the typical features of cortical thickening, osseous expansion, and trabecular coarsening. In addition, irregular bone lucency and cortical destruction are shown in the medial aspect of the shaft; this is consistent with secondary sarcoma formation.

Media file 13: Localized isotopic bone scan in the same patient as in Image 12 shows a large area of reduced uptake in the medial side of the proximal femoral shaft at the site of the secondary sarcoma (arrow).

Media file 14: Coronal T1-weighted magnetic resonance imaging (MRI) scan of the same patient as in Images 12-13. The tumor is shown in the proximal shaft of the right femur (white arrow), with cortical destruction and a large soft-tissue component (black arrow).

References

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Keywords

primary malignant tumor of bone, bone tumor, bone malignancy

Contributor Information and Disclosures

Author

Geoff Hide, MBBS, MRCP, FRCR, Consultant Musculoskeletal Radiologist, Department of Radiology, Freeman Hospital; Honorary Clinical Lecturer, Faculty of Medical Sciences, University of Newcastle upon Tyne
Geoff Hide, MBBS, MRCP, FRCR is a member of the following medical societies: British Medical Association, Royal College of Physicians, and Royal College of Radiologists
Disclosure: Nothing to disclose.

Medical Editor

Amilcare Gentili, MD, Clinical Professor of Radiology, University of California at San Diego; Consulting Staff, Department of Radiology, Thornton Hospital
Amilcare Gentili, MD is a member of the following medical societies: American Roentgen Ray Society, Radiological Society of North America, and Society of Skeletal Radiology
Disclosure: Nothing to disclose.

Pharmacy Editor

Bernard D Coombs, MB, ChB, PhD, Consulting Staff, Department of Specialist Rehabilitation Services, Hutt Valley District Health Board, New Zealand
Disclosure: Nothing to disclose.

Managing Editor

Murali Sundaram, MBBS, FRCR, FACR, Consulting Staff, Department of Diagnostic Radiology, The Cleveland Clinic Foundation
Disclosure: Nothing to disclose.

CME Editor

Robert M Krasny, MD, Consulting Staff, Department of Radiology, The Angeles Clinic and Research Institute
Robert M Krasny, MD is a member of the following medical societies: American Roentgen Ray Society and Radiological Society of North America
Disclosure: Nothing to disclose.

Chief Editor

Felix S Chew, MD, MBA, EdM, Professor, Department of Radiology, Vice Chairman for Radiology Informatics, Section Head of Musculoskeletal Radiology, University of Washington
Felix S Chew, MD, MBA, EdM is a member of the following medical societies: American Roentgen Ray Society, Association of University Radiologists, and Radiological Society of North America
Disclosure: Nothing to disclose.

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