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Flashcards in Bones & Joints Deck (253)
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61

Parosteal osteosarcoma: Presentation (2).

Painless mass of long duration.

Inability to flex the knee.

62

Parosteal osteosarcoma: Radiography (3).

Radiodense boss or fungiform mass arising outside the periosteum.

Radiolucency may separate tumor from cortex ("string sign").

No periosteal reaction.

63

Parosteal osteosarcoma: Radiolucency within the tumor (2).

Peripheral: May represent cartilage cap.

Central: May represent high-grade sarcoma.

64

Parosteal osteosarcoma: Histology

Parallel arrays of tumor osteoid.

Bland, hypocellular, fibroblastic stroma.

Cartilaginous cap or islands of cartilage containing mildly atypical, disordered chondrocytes.

65

Parosteal osteosarcoma: Variant histology.

Areas of dedifferentiation to high-grade sarcoma.

66

Parosteal osteosarcoma: What should not be seen histologically (2).

Periosteal reaction.

Fat or marrow.

67

Parosteal osteosarcoma vs. osteochondroma

Osteochondroma: Association of tumor with fat or marrow.

68

Parosteal osteosarcoma vs. myositis ossificans.

Myositis ossificans: Bone is maturer on the periphery than in the center.

69

Parosteal osteosarcoma vs. high-grade surface osteosarcoma.

High-grade surface osteosarcoma: No residual low-grade tumor.

70

Parosteal osteosarcoma vs. periosteal osteosarcoma (2).

Periosteal osteosarcoma:

- Contains more cartilage that is more malignant.
- Periosteal reaction.

71

Periosteal osteosarcoma: Sites.

Diaphysis or metaphysis:

- Tibia.
- Femur.

72

Periosteal osteosarcoma: Presentation.

Pain and swelling, usually for less than a year.

73

Periosteal osteosarcoma: Radiography (4).

Radiolucent.

Spiculated pattern of perpendicular calcifications.

There may be a periosteal reaction.

Medulla is not involved.

74

Periosteal osteosarcoma: Gross pathology.

Lobulated, cartilaginous-appearing mass on the surface.

75

Periosteal osteosarcoma: Histology (3).

Consists mainly of lobules of cartilage with features of grade 2 or grade 3 chondrosarcoma.

Malignant osteoid is an essentially but minor component.

There may be anaplastic stromal cells between cartilaginous lobules.

76

Periosteal osteosarcoma vs. conventional intramedullary osteosarcoma.

The latter involves the medullary cavity.

77

Periosteal osteosarcoma vs. high-grade surface osteosarcoma.

High-grade surface osteosarcoma lacks cartilaginous differentiation.

78

High-grade surface osteosarcoma: Sites (3).

Distal and middle femur.

Proximal humerus.

Proximal fibula.

79

High-grade surface osteosarcoma: Prognosis.

Similar to that of conventional intramedullary osteosarcoma.

Worse than that of parosteal osteosarcoma.

80

High-grade surface osteosarcoma: Radiography (3).

Similar to that of periosteal osteosarcoma, but with fluffy, "cumulus cloud" calcification.

Can cause a periosteal reaction.

No more than focal involvement of the medulla.

81

High-grade surface osteosarcoma: Histology.

High-grade, similar to that of conventional osteosarcoma, but without significant involvement of the marrow.

82

Low-grade central osteosarcoma: Sites (2).

Middle or distal femur.

Proximal or middle tibia.

83

Low-grade central osteosarcoma: Association.

Fibrous dysplasia.

84

Low-grade central osteosarcoma: Radiography (4).

Intramedullary.

Poorly circumscribed.

Sclerotic or trabeculated.

Usually no periosteal reaction.

85

Low-grade central osteosarcoma: Histology (3).

Irregular bony trabeculae.

Stroma consisting of bland fibroblast-like cells with visible nucleoli.

Rare chondroid foci may be visible.

86

Low-grade central osteosarcoma vs. fibrous dysplasia.

Fibrous dysplasia:

- Radiographically benign.
- Smooth, delicate trabeculae.
- No nuclear atypia, no mitotic activity.

87

Low-grade central osteosarcoma vs. desmoplastic fibroma.

Desmoplastic fibroma: No osteoid in the center.

88

Low-grade central osteosarcoma vs. fibroblastic variant of conventional intramedullary osteosarcoma.

The latter has greater atypia and more mitotic activity.

89

Low-grade central osteosarcoma vs. parosteal osteosarcoma.

Parosteal osteosarcoma: Similar histology but does not involve the medulla.

90

Most common tumor of bone.

Osteochondroma.