| disease | Central Osteosarcoma |
| alias | Central Chondrosarcoma |
Central osteosarcoma is a fleshy tumor, with cells tending to differentiate into cartilage. It is classified into: central osteosarcoma; peripheral osteosarcoma; and periosteal osteosarcoma. Treatment is limited to surgical intervention, with a relatively high cure rate, as radiotherapy and chemotherapy are ineffective against osteosarcoma. Due to the slow growth of osteosarcoma, local recurrence and metastasis can still occur more than a decade after the removal of the primary tumor.
bubble_chart Pathological Changes
1. Gross Appearance
In low-grade central chondrosarcoma (Grade I), the cortical bone may appear normal or show Grade I expansion without tumor infiltration, making it visually similar to benign cartilage tumors. However, in long-standing cases, Grade I central chondrosarcoma can also penetrate the cortical bone and grow significantly larger.
In Grade II–III central chondrosarcomas, the cortical bone is almost always infiltrated and disrupted by the tumor. In areas with well-differentiated cartilage, the tumor tissue retains a cartilaginous appearance, tending to form clustered polyhedral lobules. This cartilage is grayer, softer, more translucent, and contains more fluid than normal cartilage or that of benign cartilage tumors. In mucoid regions (particularly abundant and diffuse in Grade II central chondrosarcoma), the tissue is somewhat gelatinous, grayish-white, and may exhibit areas of mucoid liquefaction and hemorrhage.
In central chondrosarcoma, the tumor tissue compressed within the bone and poorly vascularized often undergoes degeneration and necrosis. Areas of cartilage degeneration may appear as white, opaque zones (resembling cooked rice), yellowish, dry necrotic areas, or cystic or hemorrhagic liquefaction. Calcifications are clearly visible, presenting as chalky, pale yellow-to-white deposits that are gritty and hard, existing as small granules or flakes, either isolated or fused, sometimes forming rings around cartilage lobules.
Unlike osteosarcoma, which rapidly invades through cortical bone, central chondrosarcoma tends to infiltrate areas of low resistance, such as the medullary cavity of the diaphysis. Thus, there can be a significant discrepancy between radiographic and anatomical findings. A central chondrosarcoma that appears radiographically confined to the epiphysis-metaphysis without cortical breach may have infiltrated the medullary cavity of the diaphysis over a considerable distance.In some cases, tumor invasion into the joint may be observed, typically in cases where the tumor volume is substantial.
2. Microscopic Findings
(1) Grade I Central Chondrosarcoma: Accounts for approximately 20%. The cartilage is well-differentiated, with minimal mucoid areas. Cytological features distinguishing it from benign cartilage tumors include: ① Larger nuclei; ② Variation in nuclear size, generally round; ③ Frequent binucleated cells, with no mitotic figures observed (cell proliferation occurs via direct division); ④ Higher cellularity compared to benign cartilage tumors.
(2) Grade II Central Chondrosarcoma: The most common form, accounting for about 60%. The cartilage tissue exhibits marked atypia, with large nuclei, characteristic hyperchromasia, frequent binucleated cells, and rare trinucleated cells. Some nuclei are 4–5 times larger than normal and/or have bizarre shapes.
(3) Grade III Central Chondrosarcoma: Accounts for approximately 20%. The cartilage is well-differentiated, with lobules surrounded by a thick cellular halo composed of densely packed, hyperchromatic chondroblasts and undifferentiated mesenchymal cells. The chondrocytes show pronounced atypia and are abundant, characterized by marked nuclear pleomorphism and hyperchromasia. The cells are often giant, 5–10 times larger than normal, with many cells containing three or more nuclei or bizarre nuclei.
bubble_chart Clinical Manifestations
Central chondrosarcoma is an intraosseous chondrosarcoma, ranking fourth among primary malignant bone tumors, following plasmacytoma, osteosarcoma, and Ewing's sarcoma. It is more common in males, with a male-to-female ratio of 1.5–2:1. It predominantly occurs between the ages of 30 and 70, mainly in adulthood, rarely before the age of 20, and is exceptionally rare before puberty.
There is a distinct predilection for specific sites, in order: the femur (especially the proximal end), pelvis, proximal humerus, scapula, and proximal tibia. Less common sites include other bones of the trunk, radius, ulna, foot, and hand (cartilaginous bone tumors are more common in the hand and rare in the trunk bones).
In long bones, central chondrosarcoma typically originates at one end of the diaphysis or the metaphysis. Since patients are usually adults whose growth cartilage has disappeared, the tumor often invades the epiphysis and may sometimes extend into the joint. Central chondrosarcoma originating from the mid-diaphysis is rare, and at diagnosis, the tumor may already involve one-third, half, or more of the long bone. In the pelvis, central chondrosarcoma frequently occurs around the acetabular region (ilium, ischium, or pubis); in the scapula, it is commonly found in the coracoid-glenoid region. Central chondrosarcoma in the pelvis and scapula can also involve large portions of the bone.
Symptoms are mild and progress slowly. The clinical history is often prolonged, sometimes presenting as a recurrent "cartilaginous bone tumor-like" mass after local surgery. The main symptom is deep, non-severe, intermittent pain. Since the tumor has not yet expanded into the soft tissues, an extraosseous mass is usually not palpable, with only slight bone enlargement observed. In advanced stages, a large spherical extraosseous mass may form.
Some cases grow rapidly and are highly aggressive, early destroying the cortical bone and invading soft tissues, forming a large soft tissue mass.
In some cases, the tumor may invade the joint from the epiphysis, causing joint symptoms. Pathological fractures are rare.
Occasionally, postoperative recurrent central chondrosarcoma may exhibit greater aggressiveness than the original tumor.
bubble_chart Auxiliary Examination
X-ray findings show osteolytic changes within the bone, which may have calcified deposits. Most tumors grow slowly, while a few grow rapidly. In the epiphyseal-metaphyseal region, the tumor is eccentric; in the diaphysis, it is located centrally.
Central osteosarcoma may present as osteolysis with blurred margins, with or without cortical interruption. Due to the tendency of cartilage to calcify and ossify, radiopaque areas may appear within the tumor. Calcification often occurs around the cartilage lobules, lacking a definite structure, and is characterized by irregular hazy granules, nodules, or radiopaque rings.
Due to bony ridges on the tumor wall, the tumor may exhibit a bubbly or breadcrumb-like appearance. If calcification is dense, the tumor may appear as a radiopaque metal-like mass. If the tumor infiltrates the medullary cavity of the cancellous bone without destroying the trabeculae, calcified deposits and reactive bone hyperplasia may present as a uniform radiopaque spongy bone. If the tumor infiltrates the cancellous bone without destroying the trabeculae and without calcification, the intraosseous portion of the tumor may not be visible. In such cases, without the aid of bone scans, CT, or MRI, the diagnosis of central osteosarcoma is difficult and delayed.
Well-differentiated central osteosarcoma shows abundant calcification, whereas grade III central osteosarcoma and dedifferentiated central osteosarcoma exhibit less calcification and more mucoid areas.
The cortical bone may be very thin, scalloped internally, and interrupted in some areas. Sometimes, due to slow tumor expansion, the cortical bone undergoes hyperplasia and may appear thickened. This thickened cortical bone is quite typical, indicating tumor infiltration.
Central osteosarcoma tends to expand into areas of lesser resistance, such as the medullary cavity of the diaphysis. In nearly half of the cases, radiographic imaging shows the tumor occupying one-third, one-half, or more of the long bone, but in the early stages, the tumor may not be visible. This characteristic is crucial; otherwise, the surgical plan may be inappropriate, and the resection margin may be insufficient. After diaphyseal resection or amputation, the tumor may recur in the residual limb. To prevent this, the extent of the tumor within the medullary cavity must be determined preoperatively using bone scans, CT, or MRI.
In more aggressive cases, central osteosarcoma may exhibit extensive cortical disruption early on, with a large soft tissue mass. The tumor invading the soft tissue shows minimal calcification. The infiltrated and elevated periosteum may reactively produce a thin, slightly radiopaque band perpendicular to the cortex, but the typical "sunburst" appearance seen in osteosarcoma and Codman's triangle are never observed.
bubble_chart Treatment Measures
The treatment for central chondrosarcoma is surgical. At initial diagnosis, most central chondrosarcomas have not yet metastasized to the lungs, so surgical resection has a relatively high cure rate, and limb-sparing treatment is often employed.
Regardless of the histological grade of central chondrosarcoma, curettage is not appropriate. Intralesional resection is only suitable for borderline cases between benign chondroid tumors and grade I central chondrosarcoma, where a cure is possible. However, such intralesional resection must be extensive and involve the use of local adjuvants such as phenol, bone cement, or liquid nitrogen.
The resection margin for central chondrosarcoma must achieve wide or radical excision. Marginal excision carries a high risk of tumor recurrence, which increases with the degree of histological malignancy. In most cases, wide excision can achieve the goal of limb preservation.
Amputation is indicated for central chondrosarcoma with large soft tissue tumors, especially in grade III central chondrosarcoma and dedifferentiated chondrosarcoma.
When planning the surgical approach, the extent of tumor invasion within the medullary cavity or cancellous bone must be precisely determined, aided by bone scans, CT, and MRI.
When central chondrosarcoma recurs in soft tissue after resection, it often lacks clear boundaries (unlike some peripheral chondrosarcomas), making en bloc resection generally unfeasible and necessitating amputation.
Central chondrosarcoma located in the trunk bones is extremely difficult to resect surgically.
Central chondrosarcoma is a radioresistant tumor, and radiotherapy is highly ineffective, even for pain relief. Chemotherapy is similarly ineffective and is only used in some cases of dedifferentiated chondrosarcoma.
If pulmonary metastases are localized, resection of the metastatic lesions should be performed.
Grade I central soft osteosarcoma generally does not metastasize. If the surgical resection is not sufficiently extensive, the tumor may recur locally. If Grade I central soft osteosarcoma invades visceral compartments or the spinal canal, it can lead to death.
Despite its slow progression and histological appearance lacking obvious malignant features, Grade II central soft osteosarcoma can metastasize early, with a high likelihood of local recurrence post-surgery. If treated promptly and adequately, the cure rate is approximately 60%.
The prognosis for Grade III central soft osteosarcoma is poor, with a survival rate of about 40%.
The prognosis of central soft osteosarcoma primarily depends on two factors: the histological grade of malignancy and the correct surgical approach (wide or radical resection, avoiding contamination).
When diagnosing central chondrosarcoma, clinical and imaging data are more important than with other tumors. Cartilaginous tumors with the same histological appearance can be either benign or malignant, and must be evaluated based on age, location, symptoms, imaging, bone scans, CT features, and other characteristics.
The preoperative diagnosis of central chondrosarcoma is often straightforward, yet the differential diagnosis involves a wide range of tumors and tumor-like lesions. First, central chondrosarcoma must be distinguished from enchondroma, particularly differentiating between grade I central chondrosarcoma and borderline malignant chondrosarcoma. Enchondromas commonly occur in children and cease growth in adulthood, often remaining unchanged for many years unless a pathological fracture occurs. Enchondromas are painless, typically of moderate size, without scalloping or disruption of the cortex, and without soft tissue swelling. In short, except for small tubular bones in the hands and feet, enchondromas usually preserve cortical integrity. Since cartilaginous tumors in the hands are almost always benign, diagnosing central chondrosarcoma in this location requires caution and should only be made when clinical, imaging, and histological findings unequivocally indicate malignancy. Conversely, cartilaginous tumors in the axial skeleton are often malignant, and unless proven otherwise, central chondrosarcoma should be considered in these locations. In doubtful cases, wide excision should be performed.
In cases of multiple enchondromas or enchondromatosis, enchondromas can grow quite large and may continue to enlarge in adulthood, characterized by histologically active proliferation. Due to the significant likelihood of transformation into central chondrosarcoma, any changes in symptoms or imaging in adults with enchondromatosis should raise suspicion of central chondrosarcoma, and biopsy should be performed promptly for definitive diagnosis.
Typical (chondroblastic) osteosarcoma occurs in childhood, whereas central chondrosarcoma rarely presents before adolescence. Even in adults, the imaging and gross pathology of these two tumors differ, but the primary distinction lies in histology. In osteosarcoma, even if the tumor cells are predominantly chondroblastic, osteogenic differentiation and direct production of osteoid by tumor cells can always be identified. Additionally, the malignancy grade (grade IV) of chondrocytes in osteosarcoma is higher than in central chondrosarcoma. However, in rare cases, differential diagnosis based on limited biopsy specimens may be difficult or even impossible. In such situations, it is advisable to repeat the biopsy with larger and more specific samples before deciding on chemotherapy.
The gross pathology of chondromyxoid fibroma can resemble that of central chondrosarcoma. Histologically, the lobulated central cells of chondromyxoid fibroma may be misdiagnosed as grade I or II central chondrosarcoma. However, the occurrence in infancy, imaging features, and typical histological characteristics of chondromyxoid fibroma aid in differential diagnosis.
