Chondromyxoid fibroma of bone is a rare benign tumor. It originates from connective tissue that forms cartilage and is easily confused with osteosarcoma or chondromyxoid fleshy tumor. Although histomorphologically, the tumor contains both chondroid tissue and myxoid material with large nuclei or bizarrely shaped nuclei among small round cells, resembling malignancy, the tumor progresses slowly and follows a benign course. Clinically, symptoms are mild, and complete surgical removal typically prevents recurrence, with metastasis being extremely rare.

bubble_chart Etiology

(1) Gross Findings The tumor often occurs in the metaphysis of large bones and generally does not invade the epiphysis. When the tumor arises in short bones, it may eventually involve the entire diaphysis. The tumor has a well-defined outline and is usually small, with a diameter ranging from 2 to 8 cm. In the cartilaginous areas, the tumor tissue appears white, slightly glossy, and firm, lacking the bluish-white color and lobulated structure typical of ordinary cartilage tissue. In the mucoid portions, the lesion appears grayish-white, soft, and brittle, without the slippery, viscous sensation characteristic of typical mucoid tissue.

(2) Microscopic Findings The tumor exhibits a lobulated structure, composed of chondroid, myxoid, and fibrous tissues. The predominant feature is spindle-shaped or stellate cells loosely distributed within a myxoid intercellular matrix. The central part of the tumor contains smaller cells, while the periphery shows denser cellularity, forming a pseudolobulated pattern. The tumor stroma may undergo collagenization, and the more mature the tumor, the more abundant the collagen fibers.

The disease is most common in adolescents, with no gender difference. 80% of cases occur in individuals under 30 years old, while it is rare in children under 10. It is frequently seen in the lower limbs, particularly in the upper tibia, femur, and lower fibula, but can also occur in the metatarsals, calcaneus, ribs, and hip bones. In rare cases, the spine may be affected. Lesions are mostly located near the metaphysis. In long bones, the tumor often grows eccentrically and may invade and destroy the local cortical bone. In short tubular bones, the tumor completely occupies the medullary cavity and causes local expansion.

Clinical symptoms are mild, primarily consisting of localized pain and swelling. Some patients may have no discomfort initially, and the tumor is only discovered through imaging after trauma.

X-ray findings In long bones, the typical presentation is a round or oval radiolucent area located eccentrically at the bone end, sometimes lobulated or honeycombed. The peripheral contour is irregular, with wavy or triangular bone ridges projecting toward the center, clearly demarcated from normal bone. The affected bone may show grade I or grade II expansion, with adjacent bone tissue exhibiting sclerosis. The tissue may also contain speckled calcifications. The local cortex is thinned, and most cases show no periosteal reaction or soft tissue mass shadows nearby. In small tubular bones, chondromyxoid fibromas are often centrally located in the medullary cavity and may involve most or all of the bone.

bubble_chart Treatment Measures

The effective treatment for this disease is complete tumor resection combined with bone grafting and surgical curettage, with a possibility of recurrence. It is generally believed that the younger the age, the higher the likelihood of recurrence. The local recurrence rate after curettage is approximately 25%, and recurrent tumors are prone to malignant transformation. Although this tumor is a benign lesion with grade I aggressiveness, distant metastasis is rare. Amputation is only considered when malignant transformation is confirmed.

1. Giant cell tumor: Most commonly found in the epiphyseal region, with significant local cortical expansion and thinning. Primarily characterized by osteolytic destruction, often with multiple intersecting linear bony septa, sometimes presenting a typical "soap bubble" appearance, and prone to pathological fracture.
2. Bone cyst: Frequently seen in the upper end of the humerus and femur. The tumor is located centrally in the metaphysis and expands outward, with a relatively uniform radiolucent area. The bony septa in multilocular bone cysts are also relatively fine.