Osteochondroma – Causes, Symptoms, Diagnosis, Treatment

Osteochondroma – Causes, Symptoms, Diagnosis, Treatment

Osteochondroma represents the most common bone tumor accounting for 20 to 50% of all benign osseous tumors. Osteochondromas are surface bone lesions composed of both cortical and medullary bone with hyaline cartilage caps. The presence of cortical and medullary continuity of the tumor with the underlying bone is a pathognomonic feature that establishes the diagnosis. Osteochondromas may be solitary or multiple. The multiple forms is an autosomal dominant syndrome referred to as hereditary multiple exostoses (HME) or familial osteochondromatosis.

Osteochondroma (osteocartilaginous exostosis), according to the 2002 WHO definition, is cartilage capped benign bony neoplasm on the outer surface of bones performed by endochondral ossification [–]. They develop and increase in size in the first decade of life and cease to grow at skeletal maturation or shortly thereafter. The most common site of involvement in the metaphyseal region of the long bones of the limbs, like the distal femur, upper humerus, upper tibia, and fibula [,]. However, osteochondromas also occur in flat bones, in particular the ilium and scapula. An important differential diagnostic feature as compared to e.g. metachondromatosis or parosteal and periosteal osteosarcoma is the extension of the medullar cavity into the lesion and the continuity of the cortex with the underlying bone. The perichondrium, the outer layer of osteochondroma, is continuous with the periosteum of the underlying bone.

Types of Osteochondroma

According to the World Health Organization (WHO), osteochondromas are bone projections enveloped by a cartilage cover that arise on the external surface of the bone. Despite their predominant composition of bone, their growth takes place in the cartilaginous portion.

They present two distinct clinical forms: single lesions (solitary osteochondromas) and several lesions (multiple osteochondromas).

Solitary osteochondroma
  • This entity is also known as an osteochondromatous exostosis, osteocartilaginous exostosis, or simply exostosis.
Multiple osteochondromas
  • Among the various synonyms used in the literature, the commonest ones are hereditary multiple exostoses, multiple cartilaginous exostoses, hereditary osteochondromatosis, and multiple hereditary osteochondromatosis.

They most commonly arise from the appendicular skeleton, especially around the knee 3:

  • lower limb: 50% of all cases
    • the femur (especially distal): most common: 30%
    • tibia (especially proximal): 15-20%
    • less common locations: feet, pelvis
  • upper limb
    • humerus: 10-20%
    • less common locations: hands, scapula
  • spine: the posterior elements of the spine are an uncommon but not rare site for these tumors

Pathophysiology

Solitary osteochondroma – Literature suggests that solitary osteochondromas may result from a developmental abnormal rather than representing a true neoplasm. The proposed hypothesis is that a fragment of the growth plate herniates through the periosteum, which then continues to grow, resulting in either a sessile or pedunculated lesion most commonly in the region of the metaphysis. The separation of the growth plate fragment can occur either spontaneously (primary osteochondroma), or secondary resulting from irradiation, surgery, or fractures (secondary osteosarcoma). However, recent studies suggest that solitary osteochondromas represent true benign neoplasms as researchers have identified genetic mutations in the gene encoding exostoses 1 (EXT1).

Hereditary multiple exostoses – The hereditary form of the osteochondroma (HME) is associated with a loss-of-function type of mutation in the tumor suppressor genes EXT1 and EXT2 that are responsible for the synthesis of heparan sulfate proteoglycans (HSPG) which results in HSPG deficiency and subsequent development of multiple osteochondromas. The importance of HSPG in the development of osteochondromas lies in its ability to interact with the bone morphogenetic proteins (BMPs) that have an essential role in the regulation of bone and cartilage formation. HME follows an autosomal dominant inheritance pattern with incomplete penetrance and a male predominance. There is a broad spectrum of EXT mutations associated with EXT1 and EXT2 genes resulting in HME. In general, patients with EXT1 mutations are more severely affected (more osteochondromas and more severe osseous deformities). Interestingly, even within family members with the same EXT mutations, there is a variable expression of the HME severity suggesting a complex incompletely understood pathophysiology.

Causes of Osteochondroma

Osteochondroma can present in the form of a solitary lesion or as a part of numerous osteochondromas in patients with multiple hereditary exostoses (HME). Some studies in the literature suggest osteochondromas are developmental lesions as oppose to true neoplasms resulting from the separation of cells from the epiphyseal growth plate.  This hypothesis has support from reported cases of osteochondroma developing following trauma or irradiation. However, more recent studies suggest that osteochondromas may truly be neoplasms as genetic mutations have appeared in both MHE and solitary forms. The categorization of solitary osteochondromas is according to the etiology into a primary and secondary osteochondroma. Primary osteochondroma develops spontaneously with no precipitating event while secondary osteochondroma can develop either due to childhood radiational exposure or due to trauma (surgery or Salter-Harris-fractures). Post-irradiation prevalence ranges from 6 to 24%, thereby representing the most common benign radiation-induced tumor. The latency period for post-radiation osteochondromas ranges from 3 to 17 years.

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Symptoms of Osteochondroma

  • A painless bump near the joints – The knee and shoulder are most often involved.
  • Pain with activity – An osteochondroma can be located under a tendon (the tough, fibrous tissue that connects muscle to bone). When it is, the tendon may move and “snap” over the bony tumor, causing pain.
  • Numbness or tingling – An osteochondroma can be located near a nerve, such as behind the knee. If the tumor puts pressure on a nerve, there may be numbness and tingling in the associated limb.
  • Changes in blood flow – A tumor that presses on a blood vessel may cause periodic changes in blood flow. This can cause a loss of pulse or changes in the color of the limb. Changes in blood flow resulting from an osteochondroma are rare.

These are the most common symptoms of osteochondroma

  • A hard, mass that is painless and does not move
  • Lower-than-normal-height for age
  • One leg or arm that is longer than the other
  • Pressure or irritation with exercise
  • Soreness of the nearby muscles
  • A hard mass that is painless and does not move
  • Lower-than-normal-height for age
  • Soreness of the nearby muscles
  • One leg or arm that is longer than the other
  • Pressure or irritation with exercise

Diagnosis of Osteochondroma

Macroscopic gross external examination

Grossly, osteochondroma is a lobulated sessile or pedunculated lesion arising from the surface of the bone with a somewhat cauliflower-like appearance.  The cartilage cap has a shiny glistening bluish to grey appearance. There is a thin fibrous capsule or perichondrium which shows continuity with the periosteum of the underlying bone. The thickness of the cartilage cap of 1 to 3 cm is considered normal in children due to the ongoing growth process. The cartilage cap is either absent or only a few millimeters in thickness in the fully mature skeleton. Cap thickness exceeding 2 cm in an adult should raise suspicion for malignancy. Varying degrees of mineralization may be present within the cartilage cap.

Macroscopic cross-sectional examination

The perichondrium, cortex, and the medulla of the osteochondroma are all continuous with the underlying bone.

Microscopic examination

Starting from the periphery, the cartilage cap that covers the tumor has a similar histological feature to the growth plate. At the junction of the cartilaginous cap and the underlying bone, evidence of endochondral ossification is visible. The medullary part is usually formed by yellow marrow rather than hematopoietic marrow through the process of endochondral ossification.

History and Physical

Solitary osteochondromas are usually asymptomatic lesions discovered incidentally on radiographs obtained for non-contributory symptoms. Symptomatic lesions may be secondary to fracture, malignant transformation, compression of adjacent neurovascular structures, bursal formation and/or bursitis, or palpable mass. When lesions are symptomatic, cross-sectional imaging is indicated to assess for the previously listed complications. Patients with HME are generally more severely affected and present at a younger age with multiple osseous deformities such as bowing of the extremities, short limbs, short stature, leg length discrepancy, coxa valgus or genu valgus.

Evaluation

Osteochondromas are often asymptomatic and may not cause any kind of discomfort. They are often found accidentally when an X-ray is done for an unrelated reason.[11]

  • X-rays – are the first tests performed that characterize a lesion. They show a clear picture of dense structures of bones, and will also indicate bone growth pertaining to osteochondroma.[5][11]
  • Computed tomography (CT) scan – can identify the bony lesion in great details and show the presence of calcification. These tests also provide great details, especially in soft tissues with the aide of cross-sectional images.
  • Ultrasound – is done if aneurysms or pseudoaneurysms and venous or arterial thrombosis is suspected. Ultrasound is an accurate method for examining the cartilaginous cap of the osteochondroma. It is also a way of pinpointing bursitis. However, it cannot be used to predict if the growth of tumor is inward in regards to the cap.[4]
  • Angiography – is used to detect vascular lesions caused by osteochondroma due to ossified cartilaginous cap. It is also used to characterize malignant transformation lesions through neovascularity.[4]
  • Clinical testing – such as sequence analysis can be done of the entire coding regions of both EXT1 and EXT2 to detect mutations.[rx]
  • A biopsy – of the tissue sample of the tumor can also be taken to check for cancer.[11]
  • MRI – also offers an exceptional assessment of other complications. Bursae show up well on T2 and PD fat-suppressed images appearing as well defined hyperintense fluid collections with or without bursitis. MRI is also useful to assess displacement and/or impingement on neurovascular structures. In patients with neurologic findings, the involved nerve may be displaced, enlarged, and/or demonstrate a hyperintense T2/PD signal. Additionally, the musculature innervated by the affected nerve may demonstrate edema (acute denervation injury), fatty infiltration (chronic denervation injury) or both. Vascular complications may include pseudoaneurysm formation, compression, or occlusion. The presentation of vascular complications will vary depending on the involvement of arterial or venous structures. In the setting of fracture, MRI will demonstrate bone marrow edema and periosteal reaction. The extent of these findings will vary with chronicity and the extent of healing.
  • Patients with HME – commonly demonstrate bowing deformities of the long bones, short stature, and short extremities. The distribution of the multiple lesions varies in the literature with some authors reporting bilateral symmetric distribution while others report unilateral. The individual lesions are similar to the solitary form with both sessile and pedunculated lesions present. Malignant transformation is more common in patients with HME, and therefore, clinical and imaging surveillance is required.
  • Bone scintigraphy – is generally not helpful as both benign and malignant lesions may demonstrate increased radiotracer activity.
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Treatment of Osteochondroma

Treatment varies from patient to patient. In the solitary form, small asymptomatic osteochondroma without suspicious imaging features requires only follow-up. However, if the lesion becomes symptomatic further assessment with cross-sectional imaging is required. Large, symptomatic lesions or lesions with suspicious imaging features such as growth in a skeletally mature patient, irregular or indistinct margins, focal areas of radiolucency, osseous erosions or destruction require surgical resection. Not surprisingly, excision of pedunculated lesions is easier than sessile lesions. Following resection, there is a 2% recurrence rate reported in the literature. Surgical intervention is much more common in patients with HME owing to both increased risk of malignant transformation and more severe osseous deformities. Surgical intervention may be performed to correct or improve the associated osseous deformities. Patients with HME undergo an average of 2.7 surgical procedures.

Nonsurgical Treatment

In most cases, treatment consists of careful observation over time. Your doctor may want to take regular x-rays to keep track of any changes in the tumors.

Indications for surgical removal of tumors are the same as for solitary osteochondromas: pain, pressure on nerves or blood vessels, and a large-cap of cartilage.

Surgical Treatment

If surgical removal of an osteochondroma is indicated, the procedure is the same as with a solitary tumor. Deformities such as knock-knees or ankles may require surgery to straighten the bone.

Should multiple osteochondromatosis become cancerous, treatment will depend on the stage of cancer’s progress. In general, malignant tumors are removed using surgery and no further treatment is recommended. Rarely, radiation therapy and chemotherapy are used in combination with surgery.

Disease associate with

The differential diagnosis for osteochondroma includes both benign and malignant lesions :

  • Subungual Exostosis (also referred to as Dupuytren exostosis) – This is a common lesion of unknown etiology, thought to arise secondary to prior trauma or infection. The lesions classically arise from the dorsal aspect of the distal phalanx near the nail bed. The lesions may be painful with associated skin ulceration. Like osteochondromas, subungual exostosis is a surface lesion. However, there is no medullary continuity. Location is also a key distinguishing feature.
  • Dysplasia Epiphysealis Hemimelica (Trevor Disease) – This is a rare process with the development of multiple osteochondromas from the epiphysis, most commonly of the lower extremities. There is a 3 to 1 male to female predominance. The process is similar to HME, presenting in young patients secondary to altered gait, osseous deformity or palpable mass. There are no reports of malignant degeneration in the literature.
  • Turret Exostosis – Extracortical mass on the back of the middle or proximal phalanx. No medullary continuity.
  • Bizarre Parosteal Osteochondromatous Proliferation (Nora lesion) – Surface lesion most commonly involving the osseous structures of the hands and feet. Unknown etiology, however, thought to be secondary to prior trauma. The lesion does not have medullary continuity. There is no reported risk of malignant degeneration.
  • Parosteal osteosarcoma – Subtype of osteosarcoma arising from the surface of long bones. Radiographs demonstrate a large, lobulated, dense osseous mass without medullary continuity; however, in advance stages, the lesion can infiltrate into the medullary space. Most commonly arises from the metaphysis of the long bones with the posterior margin of the distal femur the single most common location.
  • Juxtacortical chondroma – A surface lesion that most commonly results in the cauterization of the adjacent cortex with associated periosteal reaction. More common in patients age 20 to 40.
  • Subperiosteal hematoma – A surface lesion with a smooth superficial cortical margin with an elliptical shape arising in patients with a history of prior trauma. There is no medullary continuity. Centrally the lesion may demonstrate heterogeneity with cystic areas, mineralization or fat.

Complications

Complications of osteochondroma can range from simple cosmetic concern to serious neurological complications and malignant transformation. Complications fall under three categories, including cosmetic deformity, mechanical effect, and malignant transformation.

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Cosmetic deformity

Painless swelling is the most common complaint that triggers patients to seek medical advice due. The osseous deformity is often more severe in HME than solitary osteochondroma.

Mechanical effect

An osteochondroma can result in various complications either due to impingement and compression to adjacent neurovascular structures causing neuropathy and vascular insufficiency or due to irritation to adjacent soft tissue leading to the formation of a bursa that could be inflamed and causes pain. Neurological impingement by osteochondroma can have a wide variety of clinical presentations ranging from peripheral neurological symptoms and radiculopathy due to nerve root compression to more serious myelopathy and spinal stenosis depending on the site of the lesion. The presence of osteochondroma can compromise the blood supply to the tissues either by the formation of pseudoaneurysm or by direct compression of the adjacent blood vessels interfering with blood flow. Pseudoaneurysm formation results from the chronic repetitive mechanical compression and friction of the blood vessels by osteochondroma. Not surprisingly since the knee is the most common location of osteochondroma, popliteal pseudoaneurysm and peroneal nerve entrapment are the most common neurovascular complications. Restriction of joint motion, premature osteoarthritis, and osseous deformities affecting ADLs are other possible mechanical complications.

Malignant transformation

Malignant transformation is estimated to be 1% in solitary lesions and up to 3 to 5% in HME. An increase in size or change of radiographic appearance as previously described should raise the suspicion of malignancy. Suspicious signs of malignancy on radiograph include surface irregularity, areas of lucency and heterogeneous mineralization, and thick cartilage cap (greater than 2 cm). Chondrosarcoma is the most common form of malignant transformation. However, osteosarcoma has also been reported.

References

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