Parosteal Osteogenic Sarcoma Low Grade Osteogenic Sarcoma

Parosteal osteosarcoma rarely involves the orbit; its craniofacial involvement is usually limited to the jaw bones (Figure 16.3).31-34 It originates in the periosteum or from the immediate parosteal connective tissue and is a rare type of osteogenic sarcoma, representing about 5% of all tumors.

Accurate diagnosis and subclassification of parosteal osteosarcoma is important because although the tumor is fairly rare (approximately 16% of cases), dedifferentiation is associated with a worse prognosis. Parosteal osteosarcoma may dedifferentiate into a higher grade sarcoma, such as liposarcoma, rhabdo-myosarcoma, or malignant fibrous histiocytoma.31

Because surrounding tissue is frequently invaded by parosteal osteosarcoma, local recurrence is common. One study found as high as 46% soft tissue involvement adjacent to tumor, and 22% had adjacent

FIGURE 16.3. (A,C,D) Axial CT and MR images of focally sclerotic, well-delineated tumor of the inferior orbital rim. (B) Bone window study shows well-delineated tumor with intralesional deposits of young bone.

neurovascular bundle involvement.33 Therefore, wide excision is advocated (Figure 16.4). Along with appropriate surgical management, continued monitoring is important. Craniofacial parosteal osteosarcomas are detected early, and prognosis for these tumors, when fully excised, is better than for the conventional os-teogenic sarcoma.

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