Osteochondroma General Information Osteochondroma is an outgrowth of medullary and cortical bone A portion of the cartilaginous growth plate grows outward instead of longitudinally and forms the osteochondroma/exostosis (like a branch on a tree) It consists of bone covered with cartilaginous cap (exostosis) May be secondary to a growth plate injury (Node of Ranvier injured) Osteochondromas are benign, non-neoplastic conditions Hamartomatous anomaly It can occur as a solitary lesion or as multiple exostoses associated with a hereditary condition known as Multiple Hereditary Exostoses (MHE) Radiation exposure can also be a cause of multiple osteochondromas Solitary Osteochondromas are the most common benign bone tumors and constitute 35% of all benign bone tumors and 10% of all bone tumors overall There are 2 forms Pedunculated (with a stalk) Sessile (flat without a stalk) Osteochondromas likely arise from displaced cartilage through periosteal defect and grow at right angles to normal growth plate Lesions have self-limited growth that ceases after skeletal maturity Due to endochondral ossification, cartilage cap diminishes in thickness as age increases Osteochondroma -(most common benign neoplasm of bone that leads to biopsy) Types:
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Osteochondroma
General Information
Osteochondroma is an outgrowth of medullary and cortical bone A portion of the cartilaginous growth plate grows outward instead of longitudinally and
forms the osteochondroma/exostosis (like a branch on a tree)
It consists of bone covered with cartilaginous cap (exostosis)
May be secondary to a growth plate injury (Node of Ranvier injured)
Osteochondromas are benign, non-neoplastic conditions
Hamartomatous anomaly
It can occur as a solitary lesion or as multiple exostoses associated with a hereditary condition known as Multiple Hereditary Exostoses (MHE)
Radiation exposure can also be a cause of multiple osteochondromas
Solitary Osteochondromas are the most common benign bone tumors and constitute 35% of all benign bone tumors and 10% of all bone tumors overall
There are 2 forms
Pedunculated (with a stalk) Sessile (flat without a stalk)
Osteochondromas likely arise from displaced cartilage through periosteal defect and grow at right angles to normal growth plate
Lesions have self-limited growth that ceases after skeletal maturity
Due to endochondral ossification, cartilage cap diminishes in thickness as age increases
Osteochondroma -(most common benign neoplasm of bone that leads to biopsy)
Usually presents clinically by the third decade of life
Sites:
Appendicular skeleton: Femur (30%) Tibia (20%) Humerus (2-%) Hand and Foot (10%) Pelvis (5%) Scapula (4%)
Surface of metaphyseal portions of long tubular bones
Knee area 35% of cases
Radiographic Presentation
Plain X-rays:
Projects from bone with narrow (pedunculated) to broad (sessile) stalk Corticomedullary continuity: Medullary bone continuous with that of osteochondroma and
cortex blends with that of osteochondroma
Calcification in cartilaginous cap ("Ring and Arc" and stippled calcifications)
Lobular growth pattern
Long bones: arise from metaphysis, grows away from epiphysis toward diaphysis,
May be associated with failure of tubulation in Multiple Hereditary Exostosis
Flat bones: tend to be larger and sessile, variable appearance
Cartilage cap thickness is visualized best on MRI, not XR
Bursa may exist external to cartilage cap (seen on MRI)
Roll over the images for more information
Osteochondroma Vs. Secondary Chondrosarcoma
The cartilaginous cap deserves the most attention when differentiating a benign osteochondroma from a secondary chondrosarcoma that arose from a pre-existing osteochondroma
In adults, the cartilaginous cap regresses and becomes thin due to enchondral ossificastion of the majority of the cap.
Malignant transformation is suggested by:
Cartilaginous cap thickness greater than 2cm Cortical destruction
Backgrowth of the cartilaginous cap into the stalk or medullary canal
Lysis of calcifications in cap
Osteochondroma: Cartilage Cap
Radiographs
Chondroid Calcification in cap Increasing destruction or change in appearance is worrisome for malignancy
Ultrasound
Good for cap and bursae
Bone Scan
Increased uptake in the cap
MRI:
Best test for evaluating thickness of cap and surrounding bursa Intermediate T1W Images
High Intensity T2W Images because of fluid content
CT
The cap will appear as soft tissue with calcification Can be difficult to distinguish from muscle