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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)
Types:
Solitary Osetocartilaginous Exostosis Hereditary Multiple Exostoses (HME)
Radiographic Subtypes:
Pedunculated Sessile
Multiple Heredity Exostoses (MHE)
Clinical Data:
Male predominance (3:1) Autosomal Dominant inheritance
There is variability in size and number of ostechondromas (variable penetrance)
Any portion of the skeleton preformed in cartilage may be involved
Evident during childhood
MHE may be bilaterally symmetric
One side may predominate
There is a higher incidence of malignant transformation (10-20%) of osteochondromas that
develop in MHE. Most commonly a secondary low grade chondrosarcoma develops.
Clinical Presentation
Signs/Symptoms:
Hard swelling for many years Symptoms dependent on location/size
May cause mechanical symptoms from compression of adjacent structures such as tendons,
nerve or blood vessels
An overlying bursa may form and result in a bursitis
Rare vascular injuries and arterial aneurysms from adjacent osteochondromas
Malignant Transformation: Solitary osteochondroma <1%
Prevalence:
Male>Female 1.8:1
Age:
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
Cap thickness
Benign < 1.5cm (0.1 - 3.0cm; Avg. 0.6 - 0.9 cm) Malignant > 1.5 cm (1.5 - 12cm; Ave. 6cm)
Roll over the images for more information
Pathology
Pathology:
Medullary and cortical continuity w/ underlying bone Hyaline Cartilage Cap with lobular growth
Cartilage cap involutes after growth
Gross Pathology
The osteochondroma is completely covered in periosteum Cut surface shows hyaline composition of cartilage cap
Cap
Younger patients thicker cap because of growth hormone Smooth or knobby
2 mm to 1 cm thick
Beneath the cap, calcified cartilage which appear as white deposits are present
Roll over the images for more information
Microscopic Pathology
Roll over the images for more information
Treatment
Simple excision:
Cosmetic reasons Impingement on tendons, nerves or blood vessels
Pain and limitation of motion
For multiple exostoses, corrective surgery may be necessary due to secondary deformities
Prognosis
Recurrence after excision is rare Rarely, osteochondromas may give rise to malignant chondrosarcoma
o Solitary osteochondromas 1%-2%
o Multiple osteochondromas 5%-25%
Most common sites to undergo malignant change
o Scapula, pelvis, ribs, proximal femur
Multiple Heredity Exostoses (MHE)
Clinical Data:
Male predominance (3:1) AD inheritance
Variability in size and number
Any portion of the skeleton preformed in cartilage may be involved
Present in childhood
May be bilaterally symmetric
One side may predominate
Increased incidence of malignant transformation (10-20%)
Radiographically characterized by multiple osteochondromas and undertubulation of bones
(Erlenmeyer Flask Deformity)
Roll over the images for more information
Subungal Exostosis - Dupuytren Exostosis
Osteochondroma Variant Females > Males (2:1)
Often painful and associated with trauma and infection
Fibrocartilage cap
Located away from physis
Dysplasia Episphysealis Hemimelica - Trevor Disease
Male predominance (3:1) Very rare < 100 cases
Swelling, pain and deformity
Usually lower extremity, unilateral
65% multiple done involvement: talus, distal femur, tibia
Dysplasia Episphysealis Hemimelica - Trevor Disease
Ankle and knee most common Medial joint 2X lateral
Lobular epiphyseal mass
Histologically identical to an osteochondroma
May produce deformity and secondary osteoarthritis