Metaphysis or diaphysis of long bones, especially around the knee.
Femur, tibia, and humerus are, in this order, the more frequent locations.
Pelvis, especially the ilium, follows in frequency.
About any other bone can be more rarely affected.
Clinical Symptoms and Signs
Local pain and/or the presence of a mass is the initial symptom that can present as early as 1 week to several months.
Pathologic fracture may occur.
As this tumor is frequently associated to a preceding disease, there may be symptoms related to the primary condition.
Image Diagnosis
Radiographic and CT Features
Radiographic and CT findings correspond to a high-grade malignant lesion usually located in the metaphysis or diaphysis of a long bone.
Lytic, with no mineral deposits or ossification, poorly circumscribed, with early cortical destruction and extension to soft parts.
Periosteal reaction is unusual.
Evidence of a preceding disorder may be seen.
MRI Features
MRI shows a lesion hypo- or isointense to muscle on T1-weighted images, high signal intensity on T2, and contrast enhancement, especially at the periphery of the tumor.
Bone Scan
Bone scan demonstrates a hot lesion.
Image Differential Diagnosis
Osteosarcoma, in Young Patients
In the absence of discernible mineralized tissue, it may be impossible to differentiate by image methods.
All the following tumors may also present very similar imaging features when a single lesion is considered:
Fibrosarcoma, high grade
Leiomyosarcoma, high grade
Angiosarcoma
Malignant primary lymphoma of the bone
Metastatic carcinoma
Myeloma
Signals of a preexisting lesion can suggest the diagnosis of MFH.
Presence of multiple lesions can suggest metastasis or myeloma, which have to be screened clinically.
Pathology
Gross Features
Usually a large lesion with undefined limits either intramedullary or in its eventual soft tissue extension.
Its cut surface varies from white and fibrous (collagen producing areas) to soft (cellular areas) to tan and yellowish (lipid-laden areas) to hemorrhagic and friable (necrotic areas).
Histological Features
Histologically, MFH is characterized by a mixed population of spindle cells, histiocytic-like cells, multinucleated giant cells, all of which, including the giant cells, may be very atypical, and a chronic inflammatory infiltrate.
Specific kinds of cells may predominate in certain areas.
Spindle cell areas present a storiform or cartwheel pattern.
Histiocytic-like cells may predominate, with large clear cytoplasm and atypical nuclei.
Atypical mitoses are frequent.
Some areas may be richly vascularized, sometimes in a hemangiopericytoma-like pattern.
Foci of inflammatory infiltration are a common finding.
Giant multinucleated very bizarre cells are seen and may be abundant.
Areas with a myxoid background may be seen.
In certain tumors, the presence of intercellular hyalinized collagen matrix may be impossible to tell from osteoid. Extensive sampling may be necessary to rule out this possibility.
Pathology Differential Diagnosis
Osteosarcoma
Always contains neoplastic bone trabeculae that must be sought extensively; may present nuclear positivity with SATB2.
Fibrosarcoma, High Grade
Absolute predominance of spindle cell population
Both differential diagnosis cited above may not be of clinical importance, since these tumors will probably be treated the same way.
Liposarcoma, Pleomorphic Type
Because of the foamy aspect of some neoplastic cells
Leiomyosarcoma, High Grade
Immunohistochemical methods may be necessary in difficult cases.
Metastatic Sarcomatoid Carcinoma
Clinical and immunohistochemical methods may identify a renal tumor and characteristic immunophenotype.
Malignant Lymphoma with Fibrosis
Look for eventual multicentricity.
Spindle cells are not atypical.
Giant Cell Tumor of Bone
Epiphyseal location.
Spindle cell areas may be abundant but do not have atypical features.
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