parosteal osteosarcoma

Definition: Parosteal osteosarcomais a distinctive type of osteosarcoma that originates on the external surface of bone specifically in relation to the periostum or the immediate parosteal connective tissue or both.

Images

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Macroscopical synopsis

 hard, white, dense bone with frequent, small, peripheral, satellite nodules
 areas of fat or fibrous tissue interspersed within the lesion or in the clefts between satellites.
 areas of dedifferentiation appear soft and fleshy.
 amorphous, heavy trabeculae of disorganized bone admixed with dense, white, fibrous connective tissue.

Microscopical synospsis

 repetitive pattern of heavy trabeculae containing "Pagetoid" cement lines
 monotonous stroma of mature, spindle cells without cytologic atypia.
 nuclei of the stroma tend to be arranged parallel to each other and give the appearance of a "school of fish".
 areas of higher-grade osteosarcoma are rare and may be minute.
 mature, nonstress-oriented trabeculae are enmeshed in stroma of well-differentiated spindle cells.
 low cell-matrix ratio in the spindle cell stroma. The cells have a monotonous pattern resembling a school of fish swimming along a reef.
 long axis of the cells are parallel, there is no cellular atypia or mitoses and each cell looks exactly like the next.
 irregular, heavy cement lines in the neoplastic trabeculae and the low cell-to-matrix ratio in the stromal cells. low
 hyperchromatic spindle cells

Subtypes

 dedifferentiated parosteal osteosarcoma

See also

 opsteosarcomas