Tumor biology and incidence
- Autosomal-dominant disorder characterized by the formation of multiple osteochondromas or exostoses in the axial and appendicular skeleton
- Estimated to occur in 1 of 50,000 people
- Disease most commonly manifests itself in childhood
- 96% penetrance with variable expressivity
- Spontaneous mutation responsible for 10-20% of affected patients
- Underlying genetic cause thought to be mutation in one of several tumor suppressor genes
- Mutation in one of at least four genes has been identified at the time of writing (genes named Ext-1 to Ext-4)
Presentation
- Long bones, the pelvis, ribs, scapulam and distal ends of the proximal and distal phalanges may be affected
- Pain uncommon, but can result from nerve compression, reactive bursitis, fracture, or malignant degeneration
- Restricted range of motion can occur as a result of soft-tissue tethering or mechanical obstruction
- Skeletal abnormalities
- Short stature
- Unequal growth of the radius and ulna with radio-humeral subluxation, or Madelung deformity
- Valgus knees and ankles caused by unequal tibia and fibula growth
Physical findings
- Firm mass may be palpated
- May elicit a Tinel's sign if adjacent nerves are involved
- Mechanical features -- catching or snapping -- can be reproduced by patient if the osteochondroma is impinging on soft tissue
Radiographic studies
- Radiographic hallmarks include multiple exostoses within a single site of osseous involvement (eg, long bones, hemipelvis, spinal column)
- Exophytic projection of mature bone that demonstrates confluent trabeculae extending within the intramedullary canal in an "uninterrupted" fashion
- Stalk can be narrow (pedunculated) or broad (sessile)
- Involved metaphysis may appear flared from outward growth pattern
- Reactive changes in surrounding bone, such as lysis or sclerosis, are uncommon; may indicate malignant conversion or fracture
- Secondary imaging studies include CT and MRI, depending on whether osseous or soft tissue resolution is desired
- Cartilage cap can be well visualized on MRI, and to some extent on plain films and CT
- Usually less than 1 cm (maximal thickness); cap thickness > 2 cm is atypical, may indicate conversion to a low-grade chondrosarcoma
- CT may clarify whether a lesion communicates with the intramedullary canal (pathognomonic for osteochondroma) or arises from periosteal surface or with adjacent soft tissues
- Bone scan can be helpful to determine whether a lesion is active (increased uptake) or inactive (cold), and may help in predicting morbidity based on future growth
- Bone scan is often positive as ossification persists well into adulthood.
- Negative bone scan implies that the mass is no longer active and future growth is unlikely.
Differential Diagnosis
- Chondrosarcoma arising from osteochondroma
- Surface (parosteal) osteosarcoma (low or high grade)
- Myositis ossificans
- Bizarre parosteal osteochondromatous proliferation (BPOP)
- Heterotopic ossification
- Extraskeletal myxoid chondrosarcoma
- Tumoral calcinosis
Natural history
- Considered benign, active lesions (Enneking stage 2) during active growth
- Become benign, latent or stage 1 lesions with cessation of growth
- Conversion to malignancy estimated to range from 0.5% to 8.3%
- Chondrosarcoma most common sarcoma arising from an exostosis
Treatment
- Deformity in lower extremities may require surgical correction
- Monitor for malignant change.
- Investigate or biopsy for:
- Pain
- Enlargement after skeletal maturity
- New areas of lysis within pre-existing lesions
- Recurrence after excision suspicious for malignancy
Recommended Reading
Legeai-Mallet L, Munnich A, Maroteaux P, Le Merrer M (1997). "Incomplete penetrance and expressivity skewing in hereditary multiple exostoses". Clin. Genet. 52(1):12-6.
Kivioja A, Ervasti H, Kinnunen J, Kaitila I, Wolf M, Böhling T (2000). "Chondrosarcoma in a family with multiple hereditary exostoses". J Bone Joint Surg Br 82(2):261-6.
