parosteal osteosarcoma

(redirected from juxtacortical osteosarcoma)

pa·ros·te·al os·te·o·sar·co·ma

low-grade osteosarcoma arising on the surface of bone without involvement of the underlying marrow, usually occurring as a heavily ossified mass of the distal femur in women in the third and fourth decades of life.

parosteal osteosarcoma

An uncommon (4% of all osteosarcomas (OS)) indolent, painless OS of patients age 30 to 60, which arises in the metaphysis and is confined to the surface long bones (posterior distal femur, tibia, humerus; rarely hands or mandible). Parosteal OS lacks intramedullary involvement; it has mature lamellar bone, fibrous stroma, minimally increased cellularity, atypia and increased mitotic activity. Up to 70% arise on the surface of the distal femur. Recurrent parosteal OSs may dedifferentiate.

Imaging
Prominent extracortical calcified mass encircling bone.
 
Prognosis
Generally good—80% 5-year survival; recurrence with dedifferentiation significantly worsens the prognosis.