Fibrocartilaginous mesenchymoma is composed of two distinct tissue types: one is cartilaginous tissue, which is benign and resembles the growing epiphyseal plate; the other is similar to low-grade malignant fibrous fleshy tumor tissue. This disease is rare.

bubble_chart Pathological Changes

1. Gross appearance: The tumor is firm, white, and has a fasciculated appearance, resembling a desmoid tumor or low-grade malignant fibrous fleshy tumor. In the stroma, there are cartilage-like substances arranged in a distinctive spiral pattern, resembling a growing cartilage plate.

2. Microscopic appearance: There are continuous, intersecting spindle cells and collagen fiber bundles. Within the tumor tissue, the nuclei are plump, showing pleomorphism and hyperchromasia, with rare mitotic figures. In the stroma, there are well-demarcated cartilage islands, which are well-differentiated and exhibit benign features, often forming a thick undulating band resembling the epiphyseal plate, with progressive columnar arrangement, proliferation, and endochondral ossification. In short, the main component of fibrocartilaginous mesenchymoma resembles a grade I fibrous fleshy tumor, while another distinct component resembles the epiphyseal plate, suggesting a benign, organoid, hamartomatous characteristic.

bubble_chart Clinical Manifestations

It predominantly occurs in males, aged 9 to 23 (average 13 years). Located in the metaphysis of the proximal fibula, it only involves the epiphysis in adulthood. The tumor grows slowly and may cause grade I discomfort and tenderness. If located in superficial bones, regular, firm bone expansion with clear boundaries may be observed.

X-ray findings reveal a radiolucent lesion adjacent to the growth plate. In adults, it may invade the metaphysis, with grade II expansion of the affected bone's contour and thinning of the cortical bone, which may appear scalloped or lobulated. The cortical bone often exhibits small areas of destruction, through which the tumor extends into the surrounding soft tissues. Periosteal reaction is rare and typically shows a chronic response, resulting in a smooth or grade I rough surface of the thinned cortical bone. The tumor often contains mineral deposits—granular or ring-like patterns suggest cartilaginous components, while a cloudy appearance suggests osseous components.

bubble_chart Treatment Measures

The disease progresses slowly but is a low-grade malignant tumor. Local recurrence of the tumor is common after intralesional resection, and it may even recur several years post-surgery. Both the primary tumor and recurrent tumors should be treated with en bloc resection. No cases of metastasis have been reported.

bubble_chart Differentiation

In imaging, it needs to be differentiated from several types of tumors. Non-ossifying fibroma and low-grade malignant fibrous fleshy tumors show no mineral deposits within the mass. Soft osteosarcoma does not occur in underage patients. Chondroblastoma presents as ground-glass or cloud-like increased density rather than granular or ring-shaped. Giant cell tumor of bone is rare during the growth period and lacks mineral deposits. Pediatric osteosarcoma and adult clear cell soft osteosarcoma also require differentiation. Histologically, it should be distinguished from fibrous dysplasia, which contains cartilaginous components, but its fibrous tissue is benign. Additionally, fibrous dysplasia has bone islands, and the cartilage does not resemble growth cartilage.