Bone Tumors
Osteochondroma

James C. Wittig, MD
Sarcoma Surgeon
Orthopedic Oncologist

Osteochondroma is an outgrowth of medullary and cortical bone
A portion of the cartilaginous growth plate grows outward instead of longitudinally and forms the osteochondroma/exostosis (like a branch on a tree)
It consists of bone covered with cartilaginous cap (exostosis)
May be secondary to a growth plate injury (Node of Ranvier injured)
Osteochondromas are benign, non-neoplastic conditions
Hamartomatous anomaly
It can occur as a solitary lesion or as multiple exostoses associated with a hereditary condition known as Multiple Hereditary Exostoses (MHE)
Radiation exposure can also be a cause of multiple osteochondromas
Solitary Osteochondromas are the most common benign bone tumors and constitute 35% of all benign bone tumors and 10% of all bone tumors overall

There are 2 forms
           Pedunculated (with a stalk)
           Sessile (flat without a stalk)

Osteochondromas likely arise from displaced cartilage through periosteal defect and grow at right angles to normal growth plate
Lesions have self-limited growth that ceases after skeletal maturity
Due to endochondral ossification, cartilage cap diminishes in thickness as age increases

Osteochondroma -(most common benign neoplasm of bone that leads to biopsy)

Types:
          Solitary Osetocartilaginous Exostosis
          Hereditary Multiple Exostoses (HME)

Radiographic Subtypes:
         Pedunculated
         Sessile

Multiple Heredity Exostoses (MHE)
Clinical Data:
          Male predominance (3:1)
          Autosomal Dominant inheritance
          There is variability in size and number of ostechondromas (variable penetrance)
          Any portion of the skeleton preformed in cartilage may be involved
          Evident during childhood
          MHE may be bilaterally symmetric
          One side may predominate
          There is a higher incidence of malignant transformation (10-20%) of osteochondromas that
          develop in MHE. Most commonly a secondary low grade chondrosarcoma develops.

Prevalence:
Male>Female 1.8:1

Age:
Usually presents clinically by the third decade of life

Sites:
         Appendicular skeleton: Femur (30%) Tibia (20%) Humerus (2-%) Hand and Foot (10%) 
         Pelvis (5%) Scapula (4%)
         Surface of metaphyseal portions of long tubular bones 
         Knee area 35% of cases

Plain X-Ray:  Osteochondroma of Proximal Tibia

Proximal Fibula Osteochondroma: Cortical-Medullary Continuity; Ring and Arc Calcifications
(Top arrow)  Calcifications in Cap
(Bottom arrow)  Cortical-Medullary Continuity

MRI of Proximal Fibula Osteochondroma Demonstrates Continuity of Medullary Canal of Fibula with Osteochondroma

 

---

Intraoperative Photograph: Lobular Growth

---

Specimen

Specimen

(arrow) The Cartilage Cap

Plain Xray/MRI: Distal Femur Sessile Osteochondroma

 Xay/MRI: Distal Femur Osteochondroma

 

Gross Specimen Distal Femur Osteochondroma

Osteochondroma of Proximal Femur
(Even though this was a large tumor, the cartilage cap was very thin)

---

X-ray: Left Proximal Femur Osteochondroma

---

MRI: Left proximal Femur Osteochondroma
Cortical Medullary Continuity and Thin Cartilage Cap

Area between arrows: cartilage cap (approximately 1 cm thickness)

CT Scan: Left Proximal Femur Osteochondroma

Gross Specimen: Left Proximal Femur Osteochondroma

---

OSTEOCHONDROMA vs. SECONDARY CHONDROSARCOMA

The cartilaginous cap deserves the most attention when differentiating a benign osteochondroma from a secondary chondrosarcoma that arose from a pre-existing osteochondroma

In adults, the cartilaginous cap regresses and becomes thin due to enchondral ossificastion of the majority of the cap.

Malignant transformation is suggested by:
       Cartilaginous cap thickness greater than 2cm 
       Cortical destruction
       Backgrowth of the cartilaginous cap into the stalk or medullary canal
       Lysis of calcifications in cap

MRI: Secondary Chondrosarcoma of Proximal Femur: Thick Cartilage Cap (>2cm)

Pathology:
     Medullary and cortical continuity w/ underlying bone
     Hyaline Cartilage Cap with lobular growth
     Cartilage cap involutes after growth

The osteochondroma is completely covered in periosteum
Cut surface shows hyaline composition of cartilage cap
      Cap
            Younger patients – thicker cap because of growth hormone
            Smooth or knobby
            2 mm to 1 cm thick
Beneath the cap, calcified cartilage which appear as white deposits are present

Intraoperative Photograph: Lobular Growth
(Top arrow)  Osteochondroma
(Bottom arrow)  Fibula

Specimen

---

MICROSCOPIC PATHOLOGY

---

Hyaline cartilage cap overlying medullary bone Hyaline cartilage cap has normally appearing chondrocytes Nuclei magnified up to 5x normal diameter Mild/Moderate nuclear atypia Junction of cap and bone resembles epiphyseal plate Enchondral ossification Medullary bone contains fatty marrow

Microscopic Pathology:  Osteochondroma

(Top arrow)  Cells in Lacunae; Ground Glass Hyaline Cartilage Matrix (Middle arrow)  Zone of Hypertrophy   (Bottom arrow)  Zone of Provisional Calcification; Enchondral Ossification

Microscopic Pathology:  Osteochondroma
Junction of Cap with Medullary Bone:  Similar to Growth Plate

Simple excision:
           Cosmetic reasons
           Impingement on tendons, nerves or blood vessels
           Pain and limitation of motion
For multiple exostoses, corrective surgery may be necessary due to secondary deformities

Recurrence after excision is rare
Rarely, osteochondromas may give rise to malignant chondrosarcoma
         Solitary osteochondromas 1%-2%
         Multiple osteochondromas 5%-25%
Most common sites to undergo malignant change
         Scapula, pelvis, ribs, proximal femur

Multiple Heredity Exostoses (MHE)

Clinical Data:
      Male predominance (3:1)
      AD inheritance
      Variability in size and number
      Any portion of the skeleton preformed in cartilage may be involved
      Present in childhood
      May be bilaterally symmetric
      One side may predominate
      Increased incidence of malignant transformation (10-20%)
      Radiographically characterized by multiple osteochondromas and undertubulation of bones  
      (Erlenmeyer Flask Deformity)

X-ray: Multiple Hereditary Exostoses of Proximal Femur

X-Ray: Multiple Hereditary Osteochondromas of Scapula/Proximal Humerus