Osteochondroma overview

# Overview
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. 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%). 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.

# Historical Perspective
Osteochondroma was first described by Henry L. Jaffe, an American pathologist, in 1952.

# Classification
Osteochondromas may be classified into 2 subtypes: solitary osteochondromas (non-hereditary) and multiple osteochondromas (hereditary).

# Pathophysiology
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. 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. On microscopic histopathological analysis, osteochondroma shows cartilage cells growing in columns with a lobular arrangement.

# Causes
There are no established direct causes for osteochondroma. The development of hereditary multiple osteochondroma may be the result of multiple genetic mutations.

# Differentiating Osteoid Osteoma from other Diseases
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.

# Epidemiology and Demographics
Osteochondroma is the most common benign bone tumor among general population. 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.

# Risk Factors
Common risk factors in the development of osteochondromas, include: previous trauma to the growth plate, exposure to previous radiation, and  congenital limb anomalies.

# Screening
According to the the Canadian Society of Cancer, there is insufficient evidence to recommend routine screening for osteochondroma.

# Natural History, Complications and Prognosis
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%.

# Diagnosis

## Staging
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.

## History and Symptoms
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.

## Physical Examination
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.

## Laboratory Findings
There are no diagnostic laboratory findings associated with osteochondroma.

## X Ray
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.

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

## MRI
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.

## Ultrasound
On ultrasound, the osteochondroma cartilage cap is visualized accurately as a hypoechoic region bounded by bone.

## Other Imaging Findings
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).

## Other Diagnostic Studies
There are no other diagnostic studies for osteochondroma.

# Treatment

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

## Surgery
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).

# Primary Prevention
There is no primary prevention for osteochondroma.

# Secondary Prevention
There is no secondary prevention for osteochondroma.