Osteochondroma pathophysiology

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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]

Overview

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 in the metaphysial region of the affected bone. On microscopic histopathological analysis, osteochondroma shows cartilage cells growing in columns with a lobular arrangement.

Pathogenesis

• 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.
• A hallmark feature of osteochondromas is that they grow independently away from the nearby joint, without the need of an epiphysis.
• As the osteochondroma cartilage grows, it forms a cap over a bony mass that develops by progressive enchondral ossification.
• 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.
• Osteochondroma is a slow growing tumor which may undergo malignant transformation after a certain period of time.

Genetics

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

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

Associated Conditions

• Osteochondroma is associated with a number of syndromes that include:

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

Gross Pathology

• 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:

• 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.

Microscopic Pathology

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

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

Gallery

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  Gross pathology - osteochondroma