Osteochondroma
AKA Exostosis
Epidemiology:
- Late adolescence
and early adulthood
- Multiple osteochondromas apparent during childhood
- M:F 3:1
Common sites:
- Metaphysis of long bones, especially around
knee
- Pelvis, scapula,
ribs occasionally
- Only in bones of endochondral origin
Gross features:
- cartilage-capped
outgrowth
- attached to
underlying skeleton by a bony stalk
- solitary or
multiple
- mushroom-shaped
Histologic features:
- cap is benign
hyaline cartilage covered peripherally by perichondrium
- 3 layers:
cartilage cap, bone, marrow
- cartilage has
appearance of disorganized growth plate
- enchondral ossification
Immunophenotype:
Marker:
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Sensitivity:
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Specificity:
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Molecular features:
- inactivation of
both copies of the EXT gene in growth plate chondrocytes
Other features:
- benign
- slow-growing
- usually stop
growing at the time of growth plate closure
- rarely give rise to chondrosarcoma
(<1%) (higher in hereditary syndrome)
- multiple osteochondromas occur in multiple hereditary exostosis
- autosomal dominant inheritance
References: