bubble_chart Overview

Fibroma is fibroma, whose cells tend to differentiate into fibroblasts directionally, producing reticular fibers and collagen fibers.

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 rarely show mitotic figures. In contrast, poorly differentiated fibrosarcomas (fleshy tumors) 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 a fibrosarcoma (fleshy tumor) of the bone, the possibility of metastatic carcinoma resembling a fleshy tumor must be ruled out, especially those originating from the kidney. 1. Gross Findings: In well-differentiated and collagenized specimens, fibrosarcomas (fleshy tumors) have dense, white tissue that is quite hard. In poorly differentiated specimens, the tumor tissue is softer, liquefied, and congested due to a higher cellularity and vascularity. The color ranges from white to pink to gray, with a solid or markedly medullary appearance. Hemorrhage, necrosis, or cystic areas are common, and sometimes mucoid regions may be present.

2. Microscopic Findings: Fibrosarcomas (fleshy tumors) of the bone are graded based on their malignancy and degree of differentiation. This grading is somewhat subjective and imprecise but correlates with prognosis and treatment.

Grade I Fibrosarcoma (fleshy tumor): Distinguished from desmoid tumors. Characterized by increased cellularity, plumper nuclei, slight hyperchromasia, more pronounced pleomorphism, occasional mitotic figures, and abundant collagen fibers.

Grade II Fibrosarcoma (fleshy tumor): The tumor tissue is dense and uniform, featuring a characteristic herringbone pattern with streaming fascicles. The cells are relatively abundant, large, and spindle-shaped. 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 reticulin network is abundant and diffuse, often encircling nearly all cells. In some cases, fibers form large bundles and hyalinized collagen surrounds tumor cells, embedding them. Vascularity is relatively rich, with continuous vessel walls. Occasionally, matrix fluid absorption results in a mucoid appearance.

Grade III–IV Fibrosarcoma (fleshy tumor): Collagen fibers are scarce, and the characteristic herringbone pattern of streaming fascicles is no longer dominant, with cellularity predominating. The cells are large and exhibit marked pleomorphism. 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 (fleshy tumor), benign (reactive) multinucleated giant cells and inflammatory cell infiltration, particularly lymphocytes, may be observed.

bubble_chart Clinical Manifestations

Although it can occur at any age, it is more common in adults, with a male-to-female ratio of 2:1. It 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 peripheral types, a local mass may be the only early manifestation, with pain appearing later. In central types, symptoms intensify when pathological fractures occur. Central types are highly malignant and often metastasize via the bloodstream, whereas peripheral types are less malignant and rarely metastasize.

**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 scattered small calcifications may occasionally be seen. The adjacent cortex is locally thinned, with grade I expansion. Although the cortex is often penetrated, periosteal reaction is usually absent. In some cases, the lesion is more extensive, with disordered trabeculae interspersed with small, patchy lucent areas of bone destruction, diffusely distributed. Occasionally, minimal periosteal new bone formation is observed. Peripheral tumors are typically located in soft tissues, presenting as round or oval shadows slightly denser than muscle. A few uniform calcifications may appear within the mass. 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; cases before adolescence are rare.

The most common sites, in order, are the distal femur, proximal tibia, proximal femur, proximal humerus, and pelvis. About 50% of cases occur around the knee joint, 20% in the proximal limbs, 20% in the trunk bones, and rarely in the bones of the hands or feet.

In long bones, the tumor is usually located at one end of the diaphysis or metaphysis. In adults, it often involves the epiphysis, while purely diaphyseal localization is uncommon.

Multiple fibrous fleshy tumors are rare and typically involve one or more bones in the same limb. Concurrent or sequential involvement of both bone and soft tissue is 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-related 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 minimal or no periosteal reaction. In some cases, fibrous fleshy tumors can 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 has often already extensively invaded 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 sufficiently distant from the tumor. For example, when a fleshy tumor is located in the femur, the amputation must be performed at a high level, sometimes requiring 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, using the same regimen as for osteosarcoma, and can be attempted in high-risk cases or younger patients.

Surgical resection of pulmonary metastases is necessary and appropriate.

bubble_chart Differentiation

The imaging diagnosis of fibrous fleshy tumor is at best a hypothesis, as the imaging of fibrous fleshy tumor resembles that of all primary or metastatic malignant osteolytic tumors in adults.

The diagnosis of fibrous fleshy tumor must rely on pathology. Histologically, grade I fibrous fleshy tumor may be difficult to distinguish from desmoid tumors, but in fibrous fleshy tumor, the nuclei are more numerous, larger, plumper, with grade I hyperchromasia and marked pleomorphism, mitotic figures, less collagenous components, and immaturity. The histological distinction between fibrous fleshy tumor and benign sexually transmitted disease lesions, such as histiocytic fibroma or fibrous dysplasia, is easier. Apart from the absence of malignant features, histiocytic fibroma exhibits more pronounced whorl-like structures, hemosiderin and giant cells, and occasionally foam cells; fibrous dysplasia has fewer bundles and contains characteristic woven bone islands.