| disease | Fibrous Fleshy Tumor |
Fibrosarcoma of bone is a relatively rare malignant bone tumor. It generally originates from non-osteogenic mesenchymal tissue and the bone membrane, and can be classified into central and peripheral types. The central type arises from the medullary cavity and may eventually penetrate the cortical bone to invade soft tissues. The peripheral type originates from the bone membrane, spreading directly to invade adjacent cortical bone, and is even rarer than the central type.
bubble_chart Pathological Changes
Gross findings: Well-differentiated tumors appear gray-white, firm in texture, with fibrous strands arranged in whorls or bundles on the cut surface, and mitotic figures are rarely seen. In contrast, poorly differentiated fibrosarcomas consist of smaller cells that are round or oval, varying in size, with visible mitotic activity. The stroma contains scant collagen fibers, and the nuclei exhibit hyperchromasia, multinucleation, or nuclear atypia. It is important to note that before diagnosing fibrosarcoma of bone, the possibility of metastatic carcinoma resembling fibrosarcoma must be ruled out, especially when originating from the kidney. 1. Gross findings: In well-differentiated and collagenized specimens, fibrosarcoma tissue is dense, white, and quite firm. In poorly differentiated specimens, due to the predominance of tumor cells over fibrous tissue and increased vascularity, the tumor tissue is softer, liquefied, and congested, ranging in color from white to pink to gray. The appearance may be solid or distinctly medullary, often with areas of hemorrhage, necrosis, or cystic changes, and sometimes mucoid regions are present.
2. Microscopic findings: Fibrosarcoma of bone is graded based on its malignancy and degree of differentiation. This grading is somewhat subjective and imprecise but correlates with prognosis and treatment.Grade I fibrosarcoma: Distinguished from desmoid tumors. It is characterized by increased cellularity, plumper nuclei, slight hyperchromasia, more pronounced pleomorphism, occasional mitotic figures, and abundant collagen fibers.
Grade II fibrosarcoma: The tumor tissue is dense and uniform, featuring a fascicular and streaming pattern, typically arranged in a herringbone fashion. The cells are more abundant, relatively large, and spindle-shaped. The nuclei are plump, deeply stained, with minimal pleomorphism, and mitotic figures are common and may be irregular. Collagen fibers are relatively sparse or very scarce, while the argyrophilic reticulum is abundant and diffuse, nearly surrounding all cells. Sometimes, fibers form large bundles and hyalinized collagen rings that encase tumor cells. The vasculature is relatively rich, with continuous vessel walls. Occasionally, matrix fluid absorption results in a mucoid appearance.
Grade III–IV fibrosarcoma: Collagen fibers are sparse, and the characteristic herringbone fascicular and streaming patterns lose dominance, replaced by a cellular predominance. The cells are large with marked pleomorphism. The nuclei are hyperchromatic, atypical, occasionally bizarre or multinucleated. Mitotic figures are numerous and irregular. Blood vessels may appear cavernous, with discontinuous vessel walls.
In all grades of fibrosarcoma, benign (reactive) multinucleated giant cells and inflammatory cell infiltration, particularly lymphocytes, may be observed.
Although it can occur at any age, it is more common in adults, with a male-to-female ratio of 2:1, and frequently affects the metaphysis or diaphysis of long bones in the limbs, particularly the femur and tibia.
The main symptom is pain, which gradually worsens. In the peripheral type, a localized mass may be the only early sign, with pain appearing later. In the central type, symptoms intensify when pathological fractures occur. The central type has a higher malignancy and often metastasizes hematogenously, while the peripheral type is less malignant and rarely metastasizes.
**X-ray findings**: Central fibrous fleshy tumors primarily destroy cancellous bone, appearing on X-rays as focal lucent areas without osteogenesis. The margins are irregular, and occasional scattered small calcifications may be present. The adjacent cortex may be locally thinned, with grade I expansion. Although the cortex is often breached, periosteal reaction is usually absent. In some cases, the lesion is more extensive, with disorganized trabeculae interspersed with small patchy lucent areas of bone destruction, diffusely distributed. Occasionally, minimal periosteal new bone formation may be seen. Peripheral tumors are typically located in soft tissues, appearing as round or oval shadows slightly denser than muscle, with occasional small, uniform calcifications. The incidence is low, at least 10 times lower than that of osteosarcoma. There is no significant gender difference, or only a slight male predominance. It can occur at any age, with no notable variation between 15 and 60 years, and cases before puberty are rare.
The most common sites, in order, are the distal femur, proximal tibia, proximal femur, proximal humerus, and pelvis. Approximately 50% of cases occur around the knee joint, 20% in the proximal limbs, 20% in the axial skeleton, and rarely in the bones of the hands or feet.
Multiple fibrous fleshy tumors are rare and typically involve one or more bones in the same limb. Concurrent or sequential multifocal fibrous fleshy tumors in both bone and soft tissue are equally uncommon.
Pain is the primary symptom. In low-grade malignant fibrous fleshy tumors, swelling is mild and late, sometimes absent. However, in more aggressive cases, swelling appears earlier. Pathological fractures are common in fibrous fleshy tumors.
bubble_chart Auxiliary Examination
X-ray findings are predominantly osteolytic, strictly speaking, with no tumor-induced osteogenesis. The imaging changes are significant but lack distinct features. The osteolytic area is extensive, with blurred boundaries, cortical bone fractures, and invasion into soft tissues, with little or no periosteal reaction. In some cases, fleshy fibrous tumors may penetrate cancellous and cortical bones, producing a "moth-eaten" appearance, with small and fused osteolytic areas.
bubble_chart Treatment Measures
The primary treatment is generally surgical. Depending on the extent of the tumor and its clinical biological behavior, options include local wide excision, segmental resection, amputation, or disarticulation. Poorly differentiated tumors have an extremely poor prognosis, as local surgical treatment fails to achieve the desired outcomes. Wide resection is suitable for Grade I fleshy tumors. It may also be applied to selected cases of Grade II–IV fleshy tumors, where the tumor's location and extent allow for sufficiently wide excision. Most cases of fleshy tumors, especially Grade III–IV, require amputation. Since the tumor is often already extensively spread in the bone by the time of surgery (due to lack of symptoms and delayed timing), and the recurrence rate in the residual limb is high, the amputation site must be carefully determined. Imaging techniques such as angiography, bone scans, CT, or MRI can be referenced, and the amputation site must be far from the tumor location. For example, when the fleshy tumor is located in the femur, the amputation site must be very high, sometimes necessitating hip disarticulation or hemipelvectomy. The amputation level for fleshy tumors is often higher than that for osteosarcoma.
Fleshy tumors are not sensitive to radiotherapy, which is only used as palliative treatment for inoperable cases. Preoperative chemotherapy has no significant effect and is not routinely administered. Postoperative periodic combination chemotherapy may be considered, following the chemotherapy regimen for osteosarcoma, and can be attempted in high-risk cases or younger patients.
Surgical resection of pulmonary metastases is necessary and appropriate.
The imaging diagnosis of a fibrous fleshy tumor is at best a hypothesis, as the imaging of fibrous fleshy tumors resembles that of all primary or metastatic malignant osteolytic tumors in adults.
The diagnosis of a fibrous fleshy tumor must rely on pathology. Histologically, grade I fibrous fleshy tumors may be difficult to distinguish from desmoid tumors, but in fibrous fleshy tumors, the nuclei are more numerous, larger, and plumper, with overly dark staining, marked pleomorphism, mitotic figures, less collagenous components, and greater immaturity. Fibrous fleshy tumors are more easily distinguished histologically from benign sexually transmitted disease lesions, such as histiocytic fibromas or fibrous dysplasia, apart from the absence of malignant features. Histiocytic fibromas exhibit more pronounced whorl-like structures, contain hemosiderin and giant cells, and occasionally foam cells; fibrous dysplasia forms fewer bundles and contains characteristic woven bone islands.
