Imaging Studies
In patients with suspected bone tumors, imaging studies are the initial examinations for determining the nature and extent of the lesion. Plain radiography, magnetic resonance imaging (MRI), computed tomography (CT), and radionuclide bone imaging (ie, bone scanning) help in the differential diagnosis. Patient treatment is often based on the findings from these studies.
On conventional radiographs, pure lytic lesions define these tumors. The tumor margins are frequently permeative; however, well-defined margins have been noted. A sclerotic rim suggests another diagnosis. The lytic lesions may have fluid-filled spaces. Cortical destruction and infiltration into the surrounding soft tissues can occur. This tumor may also evoke a periosteal bone reaction, and it can be associated with the Codman triangle. A pattern of parallel striations is highly suggestive of telangiectatic osteosarcoma.
The literature regarding CT and MRI features of telangiectatic osteosarcoma is relatively sparse.
The differential diagnosis of telangiectatic osteosarcoma, based on imaging studies, often includes the following [35] :
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Aneurysmal bone cyst
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Ewing sarcoma
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Langerhans cell histiocytosis
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Fibrosarcoma
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Malignant fibrous histiocytoma
Histologic Findings
The use of fine-needle aspiration biopsy (FNAB) and the pathologic evaluation of tissue sections obtained during surgery in the diagnosis of telangiectatic osteosarcoma have been reviewed. [4, 5, 36]
Fine-needle aspiration biopsy
The examination of samples obtained by means of FNAB reveals sheets of highly polymorphous cells. The cells include spindled cells reminiscent of fibroblasts, as well as round or oval malignant cells. Multinucleated cells also are frequently identified. Nuclear hyperchromasia, nuclear membrane irregularity, and prominent nucleoli are noted in the malignant cells. Increased mitotic activity may be noted as well. The cytoplasm is variable and granular.
Although FNAB results, in conjunction with highly suggestive clinical and radiographic findings, may be of value in determining the malignant nature of the underlying process, they are not the mainstays in the diagnosis of telangiectatic osteosarcomas. Rather, core-needle or conventional biopsy permits a definitive diagnosis of telangiectatic osteosarcoma.
Gross appearance of the resected tumors
The tumors, which may be 10-20 cm in diameter, have the appearance of a hemorrhagic mass. An aneurysmal bone cyst is often suspected. Sometimes, these lesions have multicystic channels filled with blood that correspond to the radiographic appearance of fluid-filled spaces. A solid, fleshy, sarcomalike appearance is not appreciated in these lesions.
Microscopic features
Malignant cells are noted in a background of blood and necrotic debris. Because the pleomorphic hyperchromatic malignant cells may be diluted in the necrotic and hemorrhagic background, a careful examination to recognize these elements is imperative. Blood lakes, rather than endothelium-lined spaces, are present (see the image below).
Large blood lakes seen at a low magnification are reminiscent of findings in an aneurysmal bone cyst (hematoxylin and eosin, original magnification X4).
In some cases, an osteoid matrix may not be visualized except within the septal walls, which may be thin and difficult to find. In such cases, a characteristic radiographic appearance, when correlated with a careful microscopic search for features suggestive of malignancy, helps in the correct interpretation of the findings. [37] Occasionally, low-power examination reveals a morphologic pattern that is reminiscent of an aneurysmal bone cyst.
A potential trap is created by a radiologic impression of an aneurysmal bone cyst and the characteristic gross features of that cyst. However, examination of the cyst lining reveals overt malignant cells, often with increased mitotic activity (see the first image below). These cells may lie adjacent to the benign osteoclastic giant cells. In some cases, these giant cells are numerous, and the tumor mimics a giant cell–rich osteosarcoma (see the second image below).
Careful examination of the lining of blood-filled lakes shows overt malignant cells. Atypical tripolar mitosis is noted in the field (hematoxylin and eosin, original magnification X20).
Numerous giant cells may be noted in the tumor, which mimics a giant, cell–rich osteosarcoma (hematoxylin and eosin, original magnification X20).
Unlike an aneurysmal bone cyst, telangiectatic osteosarcoma has an osteoid matrix that is delicate and lacelike in appearance. Also, the stroma between the dilated vascular spaces often contains malignant cells.
Role of pathologists
A high degree of suspicion is necessary with a purely destructive long-bone lesion in adolescents. Examinations of bone tumors and tumorlike conditions have been reviewed. [12] Briefly, in the resected specimen, the size and location of the tumor and the extent of disease should be noted. The involvement of the resected margins and of the vessels, nerves, skin, and soft tissues along the biopsy tract should be included in the report.
After preoperative chemotherapy, the resected specimen should be mapped, and multiple sections representing the complete face of the bone should be obtained to document the amount of necrosis and viable tumor in the specimen. This observation is particularly important because the amount of necrosis has strong prognostic significance and affects the subsequent management of telangiectatic osteosarcoma. Tumor necrosis in more than 95-98% of the resected specimen is considered a good response to chemotherapy. [38, 39]
Staging
The American Joint Committee on Cancer (AJCC) staging system for primary bone tumors is based on a combination of the primary tumor (T), regional lymph node involvement (N), distant metastasis (M), and histopathologic grade (G). Because regional lymph node involvement is rare in bone tumors, the pathologic stage grouping involves any combination of these four grades.
With respect to these bone tumors, AJCC definitions for primary tumor characteristics are as follows:
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TX - The primary tumor cannot be assessed
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T0 - No evidence of a primary tumor is present
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T1 - The tumor is confined within the cortex
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T2 - The tumor invades beyond the cortex
Definitions for regional lymph node involvement are as follows:
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NX - Regional lymph nodes cannot be assessed
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N0 - No regional lymph node metastasis is present
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N1 - Regional lymph node metastasis is present
Definitions for distant metastasis are as follows:
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MX - Distant metastasis cannot be assessed
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M0 - No distant metastasis is present
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M1 - Distant metastasis is present
Definitions for histopathologic grades are as follows:
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GX - Grade not assessable
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G1 - Well differentiated, low grade
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G2 - Moderately differentiated, low grade
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G3 - Poorly differentiated, high grade
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G4 - Undifferentiated, high grade
Definitions for pathologic stages are as follows:
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Stage IA - G1 or G2, T1, N0, M0
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Stage IB - G1 or G2, T2, N0, M0
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Stage IIA - G3 or G4, T1, N0, M0
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Stage IIB - G3 or G4, T2, N0, M0
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Stage III - Not defined
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Stage IVA - Any G, any T, N1, M0
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Stage IVB - Any G, any T, any N, M1
Enneking initially proposed a system for staging bone tumors that was based on the histopathologic grade, the site of the lesion, and evidence of metastasis (see Table 1 below).
Table 1. Initial Enneking Clinical Staging System for Primary Malignant Bone Tumors (Open Table in a new window)
Stage |
Grade |
Location |
Metastasis |
IA |
Low grade, G1 |
T1 |
M0, intracompartmental |
IB |
Low grade, G1 |
T2 |
M0, intracompartmental |
IIA |
High grade, G2 |
T1 |
M0, intracompartmental |
IIB |
High grade, G2 |
T2 |
M0, extracompartmental |
IIIA |
Low or high grade, G1 or G2 |
T1 |
M1, intracompartmental with metastasis |
IIIB |
Low or high grade, G1 or G2 |
T2 |
M1, extracompartmental with metastasis |
In the Enneking method of staging malignant bone tumors, histologic grade is defined as follows:
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Low grade, G1 - Well-differentiated tumor with few mitoses and moderate nuclear atypia
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High grade, G2 - Poorly differentiated tumor with high cell-to-matrix ratio, many mitoses, and marked nuclear atypia
The site of the lesion is specified as follows:
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Intracapsular, T0 - Lesion surrounded by an intact capsule of fibrous tissue or reactive bone
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Extracapsular, T1 - Lesion within the compartment of its origin (the lesion remains within an intraosseous, intrafascial and/or muscular plane or periosteal or parosteal compartment)
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Extracapsular, T2 - Lesion extension beyond its compartment of origin or lesion origin within an incompletely bound space, such as the popliteal fossa, axilla, or groin
Metastasis is specified as follows:
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M0 - No known metastasis
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M1 - Metastasis present
More recently, another system, the Birmingham classification, has been proposed for the surgical staging of high-grade osteosarcoma. [40] Further study will be requried to assess the validity of this system.
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Large blood lakes seen at a low magnification are reminiscent of findings in an aneurysmal bone cyst (hematoxylin and eosin, original magnification X4).
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Careful examination of the lining of blood-filled lakes shows overt malignant cells. Atypical tripolar mitosis is noted in the field (hematoxylin and eosin, original magnification X20).
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Numerous giant cells may be noted in the tumor, which mimics a giant, cell–rich osteosarcoma (hematoxylin and eosin, original magnification X20).
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Areas of necrosis with persistent tumor cells are present after neoadjuvant chemotherapy (hematoxylin and eosin, original magnification X10).
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Anteroposterior radiograph of the distal femur shows a large, aggressive lytic lesion replacing the distal femur with no appreciable intralesional matrix. Courtesy of Robert Lopez-Ben, MD.
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Lateral radiograph of the distal femur shows a large, aggressive lytic lesion that replaces the distal femur with no appreciable intralesional matrix. Courtesy of Robert Lopez-Ben, MD.
Tables
Stage |
Grade |
Location |
Metastasis |
IA |
Low grade, G1 |
T1 |
M0, intracompartmental |
IB |
Low grade, G1 |
T2 |
M0, intracompartmental |
IIA |
High grade, G2 |
T1 |
M0, intracompartmental |
IIB |
High grade, G2 |
T2 |
M0, extracompartmental |
IIIA |
Low or high grade, G1 or G2 |
T1 |
M1, intracompartmental with metastasis |
IIIB |
Low or high grade, G1 or G2 |
T2 |
M1, extracompartmental with metastasis |
