Osteosarcoma: Radiographic Features and Imaging Strategies
Prepared for RadiologyWeb by Joseph A Gagliardi, M.D.
Table of Contents
Introduction
Part 1: Intramedullary Osteosarcoma
Part 2: Surface Osteosarcoma
Part 3: Secondary Osteosarcoma
Part 4: Extraskeletal and Gnathic Osteosarcoma
References
Figure Legend
Part 1: Intramedullary Osteosarcoma
Contributing Authors: Lustberg H1, Gagliardi JA1, Lawson JP2, Fugate M1, Micalizzi GJ1, Specht NT1.
- Department of Radiology, St. Vincent's Medical Center, Bridgeport, CT.
- Department of Radiology, Yale University, New Haven, CT.
Intramedullary or central osteosarcoma accounts for approximately 75% of all osteosarcomas [1]. More than half are found in the long bones of the knee with 90% located in the metaphyseal region (although patellar involvement is reported) [3]. Although extension through the growth plate was once thought to be rare, more recent series, particularly those utilizing MR, have shown that, histologically, a high percentage will in fact extend into the epiphysis [4]. Rarely, extension across the joint can also be seen. Osteosarcoma that originates in the diaphysis has similar clinical features to those located in the metaphysis. However, diaphyseal osteosarcoma is predominantly chondroblastic when compared to other histologic types, and can have a sclerotic margin.
Clinically, patients present with soft tissue swelling and dull intermittent pain at the tumor site, which becomes more relentless with time. A history of antecedent trauma may be obtained, but is of uncertain significance. Patients with an initial presentation of pathologic fracture are uncommon. In any apparently healthy young person with bone pain and no signs of infection or recent trauma, osteosarcoma should be suspected.
Osteosarcoma is divided into histologic subtypes which depend on cellular differentiation such as high grade or low grade, as well as the predominant internal matrix such as osteoblastic, chondroblastic, fibroblastic, fibrohistiocytic, telangiectatic and small cell [1,2]. These are all most commonly found in the bones forming the knee joint. Although there is a slight male predilection in the high grade and telangiectatic subtypes, both low grade and small cell types occur equally in males and females. Patients with low-grade intramedullary osteosarcoma tend to be slightly older with a peak occurrence in the third decade of life [1].
High grade osteosarcoma is the most common subtype, accounting for 75% of intramedullary tumors. This is an aggressive lesion that expands rapidly, invades nearby structures, and on section, frequently reveals areas of necrosis and hemorrhage due to the tumor's rapid growth.
Routine radiographs are essential in the initial work up of all osteosarcomas [5]. High grade osteosarcoma usually shows ill-defined areas of sclerosis and or lytic bone destruction with a wide zone of transition between the tumor and adjacent uninvolved bone (Figure 1). The amount of sclerosis depends not only on the amount of calcified tumor matrix and vascularity, but also on reactive bone response [6]. Soft tissue masses and periosteal reactions (Figure 2a, b) are seen in approximately 80% of patients as the tumor cells readily permeate the bone cortex [1]. The periosteal reaction can have a variable appearance including single and laminated layers of bone and perpendicular bony spicules. Osteosarcoma can also have a predominantly sclerotic (Figure 3a, Figure 4) or lytic appearance (Figure 5a, 5b).
Computed tomography (CT) will show the same features as plain film radiography but is more sensitive in detecting subtle areas of tumor bone production and showing periosteal reaction [5] (Figure 3b). In addition, CT is of value in defining the anatomy and osseous changes in those bones which are difficult to evaluate on plain film radiographs.
Magnetic resonance (MR) imaging is the modality of choice following routine radiography in the evaluation of osteosarcoma. As seen in most neoplasms, osteosarcoma is low to intermediate on T1-weighted pulse sequences that brightens on T2-weighting. Internal ossification will have low signal on both pulse sequences and areas of hemorrhage will usually be bright on all pulse sequences.
MR imaging has better soft tissue resolution in multiple planes of imaging which allows for better evaluation of tumor involvement within the overlying soft tissues, especially the neurovascular bundles. Because the articular surfaces may parallel the CT transverse plane, MR imaging can more accurately detect joint involvement. Furthermore, imaging with a large field of view makes detection of skip metastases easier (Figure 6a, 6b, 6c, 6d).
Bone marrow edema beyond the true margin of the tumor is a potential problem. However, dynamic gadolinium-enhanced images are of value in avoiding overstaging tumor size. These images also help to differentiate viable tumor from areas of cystic change and edema, but one must be aware that neovascularity in necrotic areas may also enhance.
As biopsy of any lesion causes edema, hemorrhage and inflammatory responses, all of which will interfere with the accuracy of staging, it is strongly recommended that all imaging studies be completed before any biopsy is performed.
At St. Vincent's Medical Center, all patients with an intramedullary osteosarcoma, regardless of subtype, undergo an initial radionuclide bone scan to screen for metastases, as other bones are among the two most common metastatic sites, and also to exclude the rare multifocal primary malignancies. A chest radiograph should be obtained, as the lung is the other most common site of metastatic involvement (Figure 7a). Routine CT scanning of the chest is controversial (Figure 7b).
Telangiectatic osteosarcoma is a less common intramedullary tumor that is similar to the high-grade variant with respect to patient population and tumor location. Radiographically, these lesions appear as lytic lesions with bone expansion which may be similar to an aneurysmal bone cyst [7] (Figure 8, Figure 9). On routine radiographs, penetration of the cortex by the tumor cells, with or without evidence of periosteal reaction, is a variable finding. Fluid-fluid levels can be seen on cross sectional imaging, and, again, may be similar to those seen in aneurysmal bone cysts [5]. Therefore, careful attention is needed in the diagnosis of telangiectatic osteosarcoma, as these lesions can appear identical to aneurysmal bone cysts, especially if a pathologic fracture is present which could result in an aggressive-appearing periosteal response. CT or MR imaging may demonstrate the presence of a solid-appearing peripheral rim of thick contrast enhancement, which can be nodular. This is reported to be a reliable finding for diagnosing telangiectatic osteosarcoma [5]. In contrast, thin septal or peripheral enhancement may be noted in an aneurysmal bone cyst. CT is the optimal imaging modality for detecting calcified foci due to osteoid tumor matrix. Thus, CT should be considered if the diagnosis remains in doubt after MR imaging.
Both low grade and small cell osteosarcoma are rare subtypes, each accounting for less than 5% of intramedullary osteosarcoma [1]. Low grade osteosarcoma can have features suggesting indolence, such as a thin sclerotic border or a ground glass appearance, and may simulate fibrous dysplasia, for which they can be commonly misdiagnosed. However, areas of aggressive change may be found. Periosteal reactions are rare [8].
Small cell osteosarcoma is histologically composed of small blue cells similar to round cell tumors [9]. However, these osteosarcomas produce a neoplastic osteoid matrix. Radiographically, these lesions appear like round cell lesions and have aggressive features with bone destruction, extension through the cortex and periosteal reaction [10].
References (Part 1)
1. Resnick D, Kyriakos M, Greenway GD. Tumor-like diseases of bone: imaging and pathology of specific lesions. In: Resnick D ed. Diagnosis of Bone and Joint Disorders. 3rd ed. Philadelphia: Saunders, 1995: 3648-3697.
2. Robbins SL, Coutran RS, Kumar V. Musculoskeletal pathology. In: Cotran RS, Kumar V, Collins T, Robbins SL eds. Robbins Pathologic Basis of Disease. 4th ed. Philadelphia: Saunders, 1989: 1336-1338.
3. Goodwin MA. Primary osteosarcoma of the patella. A case report. J Bone Joint Surg (Br). 1961;43:338-341.
4. Simon MA, Bos GD. Epiphyseal extension of metaphyseal osteosarcoma in skeletally immature individuals. J Bone Joint Surg (Am). 1985;62:195-204.
5. Murphy MD, Robbin MR, McRae GA, Flemming DJ, Temple HT, Kransdorf MJ. The many faces of osteosarcoma. Radiographics. 1997;17:1205-1231.
6. Greenfield GB. The solitary lesion. In: Greenfield GB ed. Radiology of Bone Disease. 4th ed. St. Louis: J.B. Lippincott, 1986: 558-582.
7. Huvos AG, Rosen G, Bretsky SS, Butler A. Telangiectatic osteogenic sarcoma: a clinicopathologic study of 124 patients. Cancer. 1982;49:1679-1689.
8. Ellis JH, Siegel CL, Martel W, Weatherbee L, Dorfman H. Radiologic features of well-differentiated osteosarcoma. Am J Roentgenol. 1988;151:739-742.
9. Sim FH, Unni KK, Beaubout JW, Dahlin DC. Osteosarcoma with small cells simulating Ewing's tumor. J Bone Joint Surg (Am). 1979; 61:207-215.
10. Edeiken J, Raymond K, Ayala AG, Benjamin RS, Murray JA, Carrasco HC. Small cell osteosarcoma. Skeletal Radiol. 1987;16:621-628.
Figure Legend (Part 1)
Figure 1. Frontal radiograph of the knee shows a mixed lytic and sclerotic lesion in the tibia with cortical destruction which was proved to be osteosarcoma.
Figure 2a. Frontal radiograph of the knee in a patient with osteosarcoma demonstrates an aggressive poorly defined lesion with areas of lytic destruction sclerosis and spiculated periosteal reaction in the tibia.
Figure 2b. Coronal T1 weighted MR image demonstrates areas of decreased signal which correlate with the area of sclerosis and areas of intermediate signal compatible with the areas of lytic bone destruction and edema. The soft tissue mass extends beyond the bony spicules which are of low signal.
Figure 3a. Lateral radiograph of the proximal tibia shows an osteosarcoma which is predominantly sclerotic.
Figure 3b. CT scan shows the sclerotic osteosarcoma, the transcortical extension with spiculation and soft tissue mass is more obvious.
Figure 4. Lateral radiograph of the left knee shows a predominantly sclerotic osteosarcoma in the femur. Note how the tumor stops abruptly at the physis.
Figure 5a, 5b. Frontal and lateral radiographs show a predominantly lytic osteosarcoma with small sclerotic focus anteriorly with spiculated periosteal reaction. (The calcifications medial to the thigh on the frontal view are in the tail of this German Shepherd.)
Figure 6a, b, c, d. Lateral radiograph of the femur in this patient shows an aggressive osteosarcoma with large soft tissue mass. The proximal extent both in the soft tissues and bone is not as clearly seen as on the MR images which show tumor foci extending into the proximal metadiaphyseal region on the coronal images. The soft tissue extension occupies almost all muscle compartments on the axial images.
Figure 7a,b. This patient with osteogenesis imperfecta and right femoral osteosarcoma showed abnormal uptake on a bone scan both in the right humerus and lung. Frontal radiograph of the humerus and CT scanning of the chest show metastatic lesions. The right humeral metastatic focus has a similar appearance to a primary osteogenic sarcoma. The lung lesion shows the typical focus of ossification seen in pulmonary mets.
Figure 8. Frontal and lateral radiographs of the knee show an expansile lytic osteosarcoma in the femur which extends to the distal epiphysis. A codman triangle is present (arrow).
Figure 9. Radiograph of the elbow shows a pathologic fracture in a telangiectatic osteosarcoma.
© 2000, RadiologyWeb
|
