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)

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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)

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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

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Microscopic Pathology

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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)

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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