Just as for osteosarcoma, fibrosarcoma has a preference for the metaphyses of long bones, especially the distal femur, with the proximal femur, distal humerus, proximal tibia, and pelvis following in frequency.
Clinical Symptoms and Signs
Local pain and/or the presence of a mass is the usual initial symptom of primary fibrosarcoma of the bone.
Limitation of motion of a neighboring joint and pathological fracture can occur in some cases at presentation.
Image Diagnosis
Radiographic and CT Features
Imaging methods show a metaphyseal eccentric lytic lesion, with a predominantly permeative pattern, without peripheral or periosteal bone reaction even after cortical permeation and soft tissue extension.
There is no sign of mineral deposits or of bone production by the tumor.
Geographical, permeative, or “moth-eaten” patterns can probably be related to different histological grades.
MRI, and bone scan do not contribute with further data for the diagnosis.
Image Differential Diagnosis
Fibroblastic Osteosarcoma and Low-Grade Central Osteosarcoma
These tumors present very scarce or variable bone production that when and if identified by imaging methods can suggest the correct diagnosis.
Desmoplastic Fibroma of Bone
Fibrosarcoma shows indistinct borders due to tumor permeation, and expansion of the cortices is unusual.
Malignant Lymphoma of Bone
In long bones, it is preferentially situated in the diaphysis. Both lesions can share the “moth-eaten” pattern; other infiltration patterns are more suggestive of fibrosarcoma.
Undifferentiated Pleomorphic Sarcoma/MFH
Has no imaging differences in relation to high-grade fibrosarcoma
Pathology
Gross Features
Fibrosarcoma presents a white and firm cut surface, with a trabeculated pattern and circumscribed margins.
Higher-grade tumors present a more fleshy appearance and focal friable necrotic or hemorrhagic areas.
Margins tend to be indistinct.
Histological Features
Fibrosarcoma is composed by a uniform spindle cell population arranged in “herringbone” or fascicular pattern.
Collagen production is variable and related to tumor grade, high-grade lesions scarcely showing collagen matrix.
By definition, there can be no other kind of matrix production except pure collagen to categorize a neoplasia as fibrosarcoma.
High-grade lesions also present more frequent mitotic and atypical nuclei as well as occasional areas of necrosis.
Pathology Differential Diagnosis
Fibrous Dysplasia
If the sample does not include immature bone trabeculae, it may be difficult to separate, on exclusively histological grounds, from well-differentiated fibrosarcoma.
Attention to infiltrated margins on histology and radiological signs of aggressiveness can help in the diagnosis.
Fibroblastic Osteosarcoma
Always contains neoplastic bone trabeculae that must be sought extensively in these predominantly fibroblastic tumors
Desmoplastic Fibroma of Bone
Has elongated strands of well-differentiated active-appearing spindle cells and is seldom permeative, less cellular, and less atypical than fibrosarcoma; mitoses, when present, are always typical.
Leiomyosarcoma of Bone
Spindle cell bundles are disposed at cross angles and present a “schoolfish” pattern different from the herring bone predominant pattern of fibrosarcoma; nuclei are elongated and blunt ended (cigar-shaped).
Positive for smooth muscle markers and keratin.
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