Bone & joints
Other chondrogenic tumors
Osteochondroma


Topic Completed: 29 December 2020

Minor changes: 4 January 2021

Copyright: 2003-2021, PathologyOutlines.com, Inc.

PubMed Search: Osteochondroma[TI] bone pathology "free full text"[SB]

Jose G. Mantilla, M.D.
Robert Ricciotti, M.D.
Page views in 2020: 20,435
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Cite this page: Mantilla JG, Ricciotti R. Osteochondroma. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/boneosteochondroma.html. Accessed January 24th, 2021.
Definition / general
  • Benign bone surface tumor composed of mature bone with a cartilage cap
  • May be solitary or occur as multiple hereditary exostoses (MHE)
Essential features
  • Exophytic lesion of bone surface composed of a stalk of mature bone with a cartilaginous cap; the marrow space / cancellous bone of the stalk communicates with that of the underlying bone
Terminology
  • Osteocartilaginous exostosis
ICD coding
  • ICD-O: 9210/0 - Osteochondroma
  • ICD-11: 2E83.Y & XH5Y87 - Other specified benign osteogenic tumors and osteochondroma
Epidemiology
  • Common, approximately 35% of benign bone tumors and 10% of all bone tumors
  • Predominance in men (M:F = 2:1)
  • Most cases diagnosed in the first 2 decades of life
Sites
  • Most common in the metaphysis of long bones: femur > humerus > tibia
  • Involvement of flat bones (ilium, scapula) may occur
  • Involvement of small bones of the hands and feet, ribs and vertebra is rare
Etiology
  • Both solitary sporadic tumors and multiple hereditary exostoses (MHE) are associated with loss of function mutations in EXT1 (8q24) and EXT2 (11p11) genes (J Genet 2015;94:749)
  • In solitary lesions, EXT gene inactivation is restricted to the cartilage cap and is somatic
  • MHE shows autosomal dominant inheritance (Am J Hum Genet 1998;62:346); patients have heterozygous germline EXT1/EXT2 mutation, while their tumors usually show homozygous EXT mutation
Clinical features
Diagnosis
  • Radiologic pathologic correlation is often specific
  • Secondary chondrosarcoma:
    • Histologic features alone are usually not definitive for diagnosis
    • Diagnosis of secondary chondrosarcoma arising in osteochondroma can be challenging and requires correlation with clinical and imaging findings (Mod Pathol 2012;25:1275, Radiology 2010;255:857, Oncogene 2012;31:1095)
    • Tumor growth and thickening of the cartilage cap (usually > 2 cm) are suggestive of malignant transformation in skeletally mature patients
Radiology description
  • Pedunculated or sessile
  • Mature bony stalk continuous with the cortex; cancellous bone of stalk communicates with that of underlying bone
  • Thin, lobulated cartilaginous cap, which may contain calcifications
  • Growth perpendicular to the long axis of the bone
Radiology images

Contributed by Jose G. Mantilla, M.D.

Osteochondroma arising in the proximal femur

Osteochondroma arising in the distal femur


AFIP images
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Distal portion of femur


Contributed by Mark R. Wick, M.D.
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Metatarsal Xray

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Xray

Prognostic factors
Case reports
Treatment
  • Growth often stops after skeletal maturity and may spontaneously regress
  • Excision is typically curative in solitary lesions, with rare local recurrence
Gross description
  • Pedunculated or sessile bony lesion with hyaline cartilage cap
Gross images

Contributed by
Jose G. Mantilla, M.D.

Hyaline cartilage cap



AFIP images
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Outer and cut surfaces

Microscopic (histologic) description
  • Cap composed of mature hyaline cartilage with overlying fibrous perichondrium
  • In young patients, transition between bone and cartilage cap resembles growth plate, showing endochondral ossification into mature bone; cartilage cap diminishes and may essentially be absent in older adults
  • Marrow elements may be present within bony stalk; marrow space / cancellous bone contiguous with that of the native bone
Microscopic (histologic) images

Contributed by Jose G. Mantilla, M.D.

Whole slide

Cartilage cap


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Whole mount section

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Cellular cartilaginous foci

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Junction of cartilage cap and underlying bone

Molecular / cytogenetics description
  • Solitary osteochondroma and MHE associated with EXT1 and EXT2 mutations
Sample pathology report
  • Knee mass, excision:
    • Osteochondroma
Differential diagnosis
  • Bizarre parosteal osteochondromatous proliferation (Nora lesion):
    • Disorganized growth of bone and cartilage with characteristic blue bone
    • Typically located in the distal extremities (J Orthop 2018;15:138)
  • Florid reactive periostitis:
    • Mixture of reactive woven bone and fibrous tissue without zonation
    • Typically arises in the periosteum of fingers
  • Parosteal osteosarcoma:
    • Similar location and age group
    • More aggressive growth areas of neoplastic woven bone formation and fibroblastic areas
    • Can have a cartilage cap in up to 25% of cases
  • Secondary chondrosarcoma:
    • Infiltrative growth with permeation of bone or extension into soft tissue
    • Usually well differentiated but with invasion into surrounding tissue
Board review style question #1
Which of the following is true about the epidemiology of osteochondromas?

  1. Congenital lesions are relatively common
  2. Female predominance
  3. Most lesions arise in long bones
  4. Most common in the elderly
  5. Multiple lesions are more common
Board review style answer #1
C. Most lesions arise in long bones

Reference: Osteochondroma

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Board review style question #2
Which of the following is true regarding secondary chondrosarcoma?

  1. Most common subtype is clear cell chondrosarcoma
  2. Patients with multiple osteochondromas have a higher overall risk of developing chondrosarcoma
  3. Risk of malignancy in patients with multiple hereditary exostosis is near 50%
  4. Risk of malignancy in solitary osteochondromas is high
Board review style answer #2
B. Patients with multiple osteochondromas have a higher overall risk of developing chondrosarcoma

Reference: Osteochondroma

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