G. Petur Nielsen, MD

Andrew E. Rosenberg, MD

An osteochondroma is shown arising from the distal femur, which is capped by mineralized cartilage and grows in a direction away from the joint. There is a linear fracture through the base of the stalk.

A typical osteochondroma that has a mushroom-shaped configuration and well-formed hyaline cartilage cap is seen. The cartilage cap overlies newly formed cancellous bone, which contains fatty marrow.



  • Osteochondroma (OCE)


  • Exostosis

  • Osteocartilaginous exostosis


  • Benign cartilage-capped tumor that originates in metaphysis or region of apophysis

  • Arises on surface of bones and enlarges through process of endochondral ossification

  • Osteochondroma occurs in 2 clinical settings

    • As solitary lesion

    • Multiple lesions (multiple hereditary osteochondromatosis)


Neoplastic Process

  • May occur sporadically, but when a manifestation of hereditary multiple osteochondromas (HMO), an autosomal dominant genetic disorder, they tend to be polyostotic and bilaterally symmetrical

  • Previously, osteochondromas were believed to develop from lateral displacement or redirection of growth plate or defects in surrounding periosteal cuff of bone

    • Based on the observation that osteochondromas never arise on surface of existing cortex and were induced experimentally in animals by manipulating the growth plate

  • Recent studies have shown that chondrocytes in cartilage cap have inactivating mutations involving genes EXT1 and EXT2 on chromosomes 8q24 and 11p11-12

    • Indicates that chondrocytes are derived from monoclonal cellular proliferation and strongly suggests that neoplastic component of osteochondromas resides in cartilage cap

  • Involvement of EXT3 on chromosome 19p also seen in some cases

  • Genetic abnormalities of osteochondroma have not been identified in dysplasia epiphysealis hemimelica or metachondromatosis

  • Small minority of osteochondromas are associated with previous radiation

    • Most patients are young

      • 25% of patients ≤ 5 years who receive total body radiation develop osteochondroma

  • Patients with metachondromatosis have both osteochondromas and enchondromas



  • Incidence

    • Most common primary bone tumor

    • Accounts for 36-50% of benign bone tumors and 8.5-15% of all primary neoplasms of bone

    • Approximately 80-85% of osteochondromas are solitary

  • Age

    • Most patients are in their 2nd decade of life at time of diagnosis

      • Incidence is 35/1,000,000 individuals 0-18 years of age

      • Age range is 8-77 years with average of 21 years

  • Gender

    • Male preponderance; M:F = 1.5-2:1


  • Typically arise in appendicular skeleton

    • In metaphysis of bones derived from endochondral ossification

      • Distal femur, proximal tibia, proximal humerus

  • Rarely arise in epiphysis

    • Known as Trevor disease or dysplasia epiphysealis hemimelica in this location

  • Can involve flat bones, such as ilium and scapula

  • Rare in small bones of hands and feet and vertebrae, and never arise in craniofacial skeleton


  • Many are asymptomatic

    • Incidental finding on imaging studies

  • Some are 1st detected as slowly enlarging firm mass present for many years

  • May be painful

    • Impingement upon adjacent neurovascular structures

    • Inflamed overlying bursa: Inflammatory bursitis

    • Fracture of stalk

  • Interferes with range of motion

Natural History

  • Slow growth that usually ceases at puberty

    • Osteochondromas exhibit greatest amount of growth while physeal plates are open

  • Malignant transformation should be considered if osteochondroma grows rapidly


  • Small and asymptomatic osteochondromas do not require intervention

    • May sustain various complications that cause them to become symptomatic and justify removal

  • Excision usually adequate therapy

    • Cortex is transected near base of lesion, which is well defined in pedunculated lesions

    • Overlying bursa should also be removed with cartilage cap

    • If portion of perichondrium or cartilage cap is left behind, then lesion may recur locally


  • Malignant degeneration of solitary osteochondroma is very uncommon (0.4-2%)

  • Development of dedifferentiated component, such as high-grade osteosarcoma or pleomorphic spindle cell sarcoma, is exceedingly rare


Radiographic Findings

  • Arises from surface of bone

  • Cortices of lesion and underlying bone and their marrow cavities are in direct continuity

  • In long tubular bones, lesion typically points away from nearest joint in reaction to forces exerted by muscles and tendons

    • Direction of osteochondroma is not diagnostic feature

  • Cartilaginous surface is lobulated and may contain calcifications

  • Base can be narrow or broad (sessile lesion)

  • Lesion can sometimes be heavily mineralized

MR Findings

  • T1-weighted image shows similar signal intensity of medullary cavity of lesion and underlying bone

  • T2-weighted image shows high signal intensity cartilaginous cap

    • Low signal intensity surrounding cap represents perichondrium

  • Helpful in evaluating thickness of cartilaginous cap

CT Findings

  • Nicely shows continuity of cortices and medullary cavity of osteochondroma and underlying bone

  • Useful in demonstrating thickness of cartilaginous cap

  • Helpful in showing bursa formation

Bone Scan

  • Hot in growing individuals

  • In adults, osteochondromas are often not hot on bone scan

    • Exceptions: Fracture, bursitis, malignant transformation


General Features

  • Mushroom shaped

  • Outer layer consists of thin sheath of fibrous tissue that overlies pearly gray-white cartilaginous cap

    • In older individuals, cartilaginous cap may be very attenuated or gone

    • May contain gritty areas of calcification or cystification

  • Cartilage cap of variable thickness; ranges from < 1 inch to several inches in depth

    • Surface of cap is smooth and lobulated

    • Base has sharp but undulating margin with underlying cancellous bone

  • Cartilage cap may demonstrate variable degrees of mineralization

    • In form of irregular stipples or ring-like calcifications

      • Due to partial or complete “framing” of cartilage lobules by ossification or amorphous mineralization

  • Base of cartilage cap undergoes enchondral ossification and merges with areas that have appearance of cancellous bone


  • 1 cm to > 20 cm in greatest dimension

    • Average: 3-6 cm


Histologic Features

  • Outer layer is perichondrium

    • Composed of dense fibrous tissue that overlies hyaline cartilage cap

    • Overall architecture recapitulates that of disorganized growth plate

  • Peripheral portion of cap is least cellular with individual chondrocytes surrounded by abundant hyaline cartilage matrix

  • Cellularity of cartilage increases in deeper layers

  • Chondrocytes become arranged in vague columns

  • In deeper layers, chondrocytes enlarge with more abundant cytoplasm

  • Chondrocytes exhibit minimal cytologic atypia and no mitotic activity

    • Scattered binucleate cells may be present

  • Matrix calcifies at base of cap

  • Chondrocytes undergo necrosis

    • Portions of mineralized cartilage are resorbed by osteoclasts at base of cap

    • Residual struts of cartilage matrix that are left behind act as scaffolding for bone deposition

  • Newly formed trabeculae mimic primary spongiosa at base of normal growth plate


Bizarre Parosteal Osteochondromatous Proliferation (BPOP)

  • Contains reactive fibrous tissue that overlies cellular cap of cartilage, which undergoes enchondral ossification

  • Underlying cortex is intact

Periosteal Myositis Ossificans

Jul 6, 2016 | Posted by in PATHOLOGY & LABORATORY MEDICINE | Comments Off on Osteochondroma

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