Extraskeletal osteosarcoma is an osteosarcoma that arises in soft tissues. It can be classified into myxoid, mesenchymal, and differentiated types. Since the differentiated type is very rare, only extraskeletal myxoid osteosarcoma will be discussed here.

bubble_chart Pathological Changes

1. Extraskeletal myxoid osteosarcoma

(1) Gross findings The tumor appears multinodular with an intact membrane, showing a lobulated cut surface, gelatinous in texture, and may exhibit areas of hemorrhage and cystic degeneration.

(2) Microscopic findings The cells are distributed in a lobular pattern, with small tumor cells arranged in cords within the abundant mucoid matrix of each lobule. Chondroblasts can be observed, featuring eosinophilic cytoplasm, vacuolated cells, and small hyperchromatic nuclei.

2. Extraskeletal mesenchymal fleshy tumor

(1) Gross findings The tumor is relatively large and multinodular, with a grayish-white fish-flesh-like cut surface, and may contain scattered small cartilage-like tissues.

(2) Microscopic findings The tumor is composed of undifferentiated mesenchymal cells, which are spindle-shaped with hyperchromatic nuclei and scant cytoplasm. Well-differentiated island-like cartilage tissues can be seen, with possible calcification at the center of the cartilage.

bubble_chart Clinical Manifestations

1. Extraskeletal myxoid osteosarcoma mostly occurs in middle-aged individuals, with an average age of around 50, and is more common in males than females. It is frequently found in the thigh and around the knee joint, usually deep within the muscles.

2. Extraskeletal mesenchymal fleshy tumor predominantly affects young women aged 15 to 35 and is commonly seen in the head and neck region. It can also occur in the limbs and retroperitoneum.

1. Extraskeletal myxoid osteosarcoma: Radical tumor resection is performed. Since this tumor grows relatively slowly, the prognosis is generally favorable. However, metastasis can still occur.

2. Extraskeletal mesenchymal fleshy tumor: Wide local excision is required. Due to the high incidence of pulmonary metastasis, the prognosis is poor.

bubble_chart Differentiation

1. Extraskeletal myxoid osteosarcoma should be differentiated from myxoid liposarcoma and myxoid malignant fibrous histiocytoma.

2. Extraskeletal mesenchymal chondrosarcoma should be differentiated from synovial sarcoma.