Osteochondroma

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]Associate Editor(s)-in-Chief: Maria Fernanda Villarreal, M.D. [2]

Osteochondroma (also known as “osteocartilaginous exostosis”) is a benign bone tumor that consists of cartilage and bone. Osteochondromas arise from cartilage, which is normally involved in the mechanical support of the bone. These tumors take the form of cartilage-capped bony projections or outgrowth on the surface of bones, also known as exostoses.^[1] Osteochondroma is the most common benign bone tumor and usually occurs in the metaphyseal region of the long bones. Osteochondromas may be classified into 2 subtypes: solitary osteochondromas (non-hereditary) and multiple osteochondromas (hereditary); the majority of these tumors present as solitary lesions (85%).^[2] Development of osteochondromas is the result of the developmental anomaly of skeletal growth. Genes involved in the pathogenesis of osteochondroma include EXT1 and EXT2 genes. Osteochondroma is associated with a number of syndromes that include Langer-Giedion syndrome, Potocki-Shaffer syndrome, and metachondromatosis syndrome. Osteochondromas are usually found in adolescents and children. Males are more commonly affected with osteochondroma than females. The incidence of osteochondroma is approximately 0.9 per 100,000 individuals. If left untreated, progression occurs slow and is then followed by malignant transformation. The treatment choice for osteochondroma is surgical removal of solitary lesion or partial excision of the outgrowth.

Osteochondroma was first described by Henry L. Jaffe, an American pathologist, in 1952.^[3]

Osteochondromas may be classified into 2 subtypes: solitary osteochondromas (non-hereditary) and multiple osteochondromas (hereditary).^[2]

Osteochondroma arises from the cartilage cells (chondrocytes), which are normally involved in the mechanical support of the bone. The pathogenesis of osteochondroma consists of abnormal outgrowth of bone and cartilage, associated with the aberrant development of the growth plate.^[2] Genes involved in the pathogenesis of osteochondroma include EXT1 and EXT2 genes. Osteochondroma is associated with a number of syndromes that include Langer-Giedion syndrome, Potocki-Shaffer syndrome, and metachondromatosis syndrome. On gross pathology, osteochondromas have a “mushroom-like shape”, the tumor size ranges from 1 to 2 cm, and they are normally located on the metaphysial region of the affected bone.^[4] On microscopic histopathological analysis, osteochondroma shows cartilage cells growing in columns with a lobular arrangement.^[5]

There are no established direct causes for osteochondroma. The development of hereditary multiple osteochondroma may be the result of multiple genetic mutations.^[2]

Osteochondroma must be differentiated from other diseases that cause bone deformity, bone growth, overlying bursitis, and mechanical joint problems such as enchondroma, chondroblastoma, periosteal chondroma, and chondromyxoid fibroma.^[2]

Osteochondroma is the most common benign bone tumor among general population.^[6] The incidence of osteochondroma is approximately 0.9 per 100,000 individuals in the general population. The incidence of osteochondroma decreases with age; the median age at diagnosis is between 10 to 13 years. Males are more commonly affected with osteochondroma than females. Osteochondroma usually affects individuals of the Caucasian race.^[2]

Common risk factors in the development of osteochondromas, include: previous trauma to the growth plate, exposure to previous radiation, and congenital limb anomalies.^[6]

According to the the Canadian Society of Cancer, there is insufficient evidence to recommend routine screening for osteochondroma.^[7]

If left untreated, patients with osteochondroma may progress to develop overlying bursitis, vascular compromise, and rise to malignant chondrosarcoma. Common complications of osteochondroma include fracture, osseous deformation, and growth arrest. Prognosis is generally regarded as good after surgical excision. The recurrence rate of osteochondroma is 2%.^[6]

According to the Musculoskeletal Tumor Society (MSTS) classification, there are 3 stages of osteochondroma based on the tumoral activity. Each stage is assigned a number that designate the level of bone erosion. The different stages of osteochondroma, include: stage I, stage II, and stage III.^[8]

The hallmark of osteochondroma is a painless growing mass. A positive history of Langer-Giedion syndrome, Potocki-Shaffer syndrome, or metachondromatosis syndrome is highly suggestive of multiple osteochondromas. Symptoms related with osteochondroma will vary depending on the size and location of the tumor. Common symptoms of osteochondroma may include limb numbness, adjacent muscle soreness, and claudication.^[2]

Physical examination findings of osteochondroma will depend on the location of the tumor. Physical examination of patients with osteochondroma is usually remarkable for bone deformity, limited range of limb motion, loss of pulse, and color change.^[2]

There are no diagnostic laboratory findings associated with osteochondroma.

On conventional radiography, characteristic findings of osteochondroma include: sessile or pedunculated bony growth, located at the metaphyseal region, bone growth projecting away from the epiphysis, and widening of the metaphysis.^[9]

On CT scan, osteochondroma shows the same findings as on radiograph, but it has better accuracy to demonstrate medullary continuity and the cartilage cap.^[9]

On MRI, osteochondroma shows cartilage thickness (and thus assessing for malignant transformation), presence of edema in bone or adjacent soft tissues, and visualization of neurovascular structures. MRI is the imaging modality of choice to assess malignant transformation of osteochondroma.^[9]

On ultrasound, the osteochondroma cartilage cap is visualized accurately as a hypoechoic region bounded by bone.^[9]

Other imaging findings, include nuclear medicine (bone scintigraphy) in which osteochondroma shows increased uptake on bone scans. Conversely, presence of increased activity in adults should raise the possibility of a complication (e.g. fracture, malignancy).^[9]

There are no other diagnostic studies for osteochondroma.^[9]

There is no medical treatment for osteochondroma; Observation surveillance is suggested if lesions are asymptomatic.

Surgery is the mainstay of therapy for osteochondroma. Surgery for osteochondroma should be considered, until bone growth is complete (assessed by mature skeleton x-ray evaluation).^[10]

There is no primary prevention for osteochondroma.

There is no secondary prevention for osteochondroma.

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor(s)-in-Chief: Maria Fernanda Villarreal, M.D. [2]

Osteochondroma was first described by Henry L. Jaffe, an American pathologist, in 1952.^[1]

Osteochondroma was first described by Henry L. Jaffe, an American pathologist, in 1952.^[1]

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor(s)-in-Chief: Maria Fernanda Villarreal, M.D. [2]

Osteochondromas may be classified into 2 subtypes: solitary osteochondromas (non-hereditary) and multiple osteochondromas (hereditary).^[1]

The table below differentiates between the 2 subtypes of osteochondromas:^{[1][2][3][4][5][6][7][8]}

Type of Osteochondroma	Features
Solitary osteochondroma	Non-hereditary 85% of osteochondromas No genetic mutations Located in long bones Onset is in early adolescence
Multiple osteochondromas	Hereditary Approximately 20% of osteochondromas Related genetic mutations EXT-1 and EXT-2 Early onset of disease (newborn or children)

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]Associate Editor(s)-in-Chief: Maria Fernanda Villarreal, M.D. [2]

Osteochondroma arises from the cartilage cells (chondrocytes), which are normally involved in the mechanical support of the bone. The pathogenesis of osteochondroma consists of abnormal outgrowth of bone and cartilage, associated with the aberrant development of the growth plate.^[1] Genes involved in the pathogenesis of osteochondroma include EXT1 and EXT2 genes. Osteochondroma is associated with a number of syndromes that include Langer-Giedion syndrome, Potocki-Shaffer syndrome, and metachondromatosis syndrome. On gross pathology, osteochondromas have a “mushroom-like shape”, the tumor size ranges from 1 to 2 cm, and they are normally located in the metaphysial region of the affected bone.^[2] On microscopic histopathological analysis, osteochondroma shows cartilage cells growing in columns with a lobular arrangement.^[3]

• Osteochondroma arises from the cartilage cells (chondrocytes), which are normally involved in the mechanical support of the bone.
• The pathogenesis of osteochondroma consists of abnormal outgrowth of bone and cartilage, associated with the aberrant development of the growth plate.^[3]
• A hallmark feature of osteochondromas is that they grow independently away from the nearby joint, without the need of an epiphysis.^[4]
• As the osteochondroma cartilage grows, it forms a cap over a bony mass that develops by progressive enchondral ossification.^[5]
• The bony portion of the osteochondroma contains both cortical and medullary bone with the marrow space contiguous with the parent bone.
• Osteochondromas have their own growth plate and will the tumor growth will stop after a certain age due to the skeletal maturity of the growth plate.
• Osteochondroma usually presents as a solitary cartilage-capped bony outgrowth protruding from the bone surface at the metaphysis of long bones.
• Osteochondroma is usually located in the metaphyseal region of the long bones. Common anatomical locations include: the femur, the proximal tibia, and the proximal humerus. These locations account for 65-85% of cases.^[5]
• Osteochondroma is a slow growing tumor which may undergo malignant transformation after a certain period of time.

• Development of osteochondroma is the result of multiple genetic mutations.
• Genes involved in the pathogenesis of osteochondroma include:^[6]

• Germ line mutation in EXT1 gene located on chromosome 8q24.11-q24.13
• Germ line mutation in EXT2 gene located on chromosome 11p11-12

• Osteochondroma is associated with a number of syndromes that include:^[1]

• Langer-Giedion syndrome
• Potocki-Shaffer syndrome
• Trevor disease
• Metachondromatosis syndrome

• On gross pathology, osteochondroma is an irregular mass with a “mushroom-like shape”, a bluish gray cap of cartilage, which is usually located at the metaphysial region of the affected bone.
• Other gross pathology findings, include:^[2]

• Tumor size ranges from 1 to 2 cm.
• Opaque yellow cartilage with calcification in the matrix.
• The base of the lesion has a rim of cortical bone and central cancellous bone.
• The cartilage cap is usually thin (1-6 mm); irregular and thick cap (> 2 cm) may be indicative of malignant transformation.

• On microscopic histopathological analysis, the characteristic feature of osteochondromas is the presence of cartilage-like extracellular tumor matrix.^[3]
• Other histopathological features of osteochondroma, include:

• The presence of cartilage cells growing in columns with a lobular arrangement.^[3]
• Mild atypia with nuclear enlargement.
• The perichondrium demonstrates a thin layer of cells with higher cellular density than cartilage.

• 
  Bone – osteochondroma^[2]
• 
  Bone – osteochondroma^[2]
• 
  Bone – osteochondroma^[2]
• 
  Bone – osteochondroma^[2]
• 
  Gross pathology – osteochondroma^[2]

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]Associate Editor(s)-in-Chief: Maria Fernanda Villarreal, M.D. [2]

There are no established direct causes for osteochondroma. The development of hereditary multiple osteochondroma may be the result of multiple genetic mutations.^[1]

• There are no established direct causes for osteochondroma.^[2]
• The development of hereditary multiple osteochondroma may be the result of multiple genetic mutations.^[1]
• Common genetic mutations for the development of osteochondroma can be found here.^[3]

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor(s)-in-Chief: Maria Fernanda Villarreal, M.D. [2]

Osteochondroma must be differentiated from other diseases that cause bone deformity, bone growth, overlying bursitis, and mechanical joint problems such as enchondroma, chondroblastoma, periosteal chondroma, and chondromyxoid fibroma.^[1]

• The table below summarizes the findings that differentiate osteochondroma from other conditions that cause bone deformity, bone growth, overlying bursitis, and mechanical joint problems.^{[1][2][3][4][5]}

Disease	Malignant lesion in patients > 40 years	chondrogenic Histology	Sacral lesions in elderly	Treatment is wide resection alone
Chondrosarcoma	+	+	+	+
Metastic disease	+	–	+	–
Lymphoma	+	–	+	–
Myeloma	+	–	+	–
Malignant Fibrous Histiocytoma	+	–	+	–
Secondary sarcoma	+	–	–	–
Enchondroma	–	+	–	–
Periosteal chondroma	–	+	–	–
Osteochondroma	–	+	–	–
Parosteal osteosarcoma	–	–	–	+
Adamantinoma	–	–	–	+
Chordoma	–	–	–	+
Squamous cell carcinoma	–	–	–	+

Differential Diagnosis	Similar Features	Differentiating Features
Enchondroma	Benign cartilaginous neoplasm Usually found in children, enchondromas are asymptomatic These tumors arise from remnants of the growth plate Located in the metaphyseal region	Imaging features, such as: Endosteal scalloping Well circumscribed mass Lytic lesions
Chondroblastoma	Benign cartilaginous neoplasm Affects young patients Located on long bones	They arise in the epiphysis or apophysis of a long bone Classical location is the upper one-third of the tibia
Periosteal chondroma	Benign cartilaginous neoplasm Commonly located on the proximal humerus and distal femur Affects young patients	Symptomps are usually present for a long period of time Imaging features, include: No stalk or peduncle as in an osteochondroma
Chondromyxoid fibroma	Benign cartilaginous neoplasm Located in the metaphyseal region of long bones	Occur in young adults (second and third decades) Usually located in the tibia

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]Associate Editor(s)-in-Chief: Maria Fernanda Villarreal, M.D. [2]

Osteochondroma is the most common benign tumor of the bone.^[1] The incidence of osteochondroma is approximately 0.9 per 100,000 individuals in the general population. The incidence of osteochondroma decreases with age; the median age at diagnosis is between 10 to 13 years.^[2] Males are more commonly affected with osteochondroma than females. Osteochondroma usually affects individuals of the Caucasian race.^[3]

• Osteochondroma is the most common benign bone tumor among general population.
• Osteochondroma is considered an uncommon tumor among adults, as it comprises fewer than 20% of all bone tumors among that age group.^[4]

• The overall adjusted incidence rate of osteochondroma is approximately 0.9 per 100,000 individuals in the general population.^[3]

• The incidence of osteochondroma decreases with age; the median age at diagnosis is between 10 to 13 years.
• The subtypes of osteochondroma has an influence on the age of presentation such as:

• Hereditary multiple osteochondroma presents among younger children or newborns
• Single osteochondroma presents among infants and adolescents

• Males are more commonly affected with osteochondroma than females. The male to female ratio is approximately 2 to 1.^[5]
• In multiple osteochondromas, males are more commonly affected by severe manifestations than females.

• Osteochondroma usually affects individuals of the Caucasian race.
• The incidence rate of osteochondroma among Caucasians is 2 per 100,000 individuals in the general population.^[3]

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor(s)-in-Chief: Maria Fernanda Villarreal, M.D. [2]

Common risk factors in the development of osteochondromas, include: previous trauma to the growth plate, exposure to previous radiation, and congenital limb anomalies.^[1]

Common risk factors in the development of osteochondromas, include:^[1]

• Previous trauma to the growth plate
• Exposure to previous radiation
• Congenital limb anomalies

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor(s)-in-Chief: Maria Fernanda Villarreal, M.D. [2]

According to the the Canadian Society of Cancer, there is insufficient evidence to recommend routine screening for osteochondroma.^[1]

According to the the Canadian Society of Cancer, there is insufficient evidence to recommend routine screening for osteochondroma.^[1]

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]Associate Editor(s)-in-Chief: Maria Fernanda Villarreal, M.D. [2]

If left untreated, patients with osteochondroma may progress to develop overlying bursitis, vascular compromise, and rise to malignant chondrosarcoma. Common complications of osteochondroma include fracture, osseous deformation, and growth arrest. Prognosis is generally regarded as good after surgical excision. The recurrence rate of osteochondroma is 2%.^[1]

• Most patients with osteochondroma are initially asymptomatic.^[2]
• The symptoms of osteochondroma usually develop in the first and second decade of life, and initially patients complain of bone pain that is increased upon activity.
• If left untreated, patients with osteochondroma may develop a palpable lump, bursitis, and malignant transformation.^[1]

• Common complications of osteochondroma, include:^[3]

• Bone fracture
• Growth arrest
• Osseous deformation
• Pseudoaneurysm
• Cosmetic deformities
• Impingement on adjacent structures
• Secondary arthritis

• Osteochondroma prognosis is generally regarded good after surgical excision.^[4]
• The overall recurrence rate after resection is 2%.^[1]
• The prognosis for malignant transformation of osteochondroma will depend on the histological grade, such as:^[2]

• The 10-year survival rate of patients with grade I chondrosarcoma is approximately 83%
• The 10-year survival rate of patients with grade III chondrosarcoma is approximately 29%

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