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Enchondroma

Definition

  • Benign intramedullary cartilage tumour producing mature hyaline cartilage

Aetiology

  • Popular theory is
    • Arise from the physis as cell rests
    • Fail to undergo endochondral ossification & deposited into the metaphysis
    • Moves into diaphysis as it grows
  • Central location = Enchondroma
  • Outside the cortex = Periosteal or Juxtacortical Chondroma

Incidence

  • Most seen in the 2nd-4th decades
  • No sex prediliction
  • Start near physis (metaphyseal) but may become diaphyseal
  • Involves any bone formed by enchondral ossification
  • Most common sites
    • Short tubular bones of hand (50%) especially phalanges
    • Femur
    • Humerus
    • Ribs

Clinical Features

  • Young adults
  • Usually incidental finding
  • May be pathological fracture

Radiology

  • X-ray
    • Well-defined centrally located radiolucent lesion
    • Often located at junction of metaphysis & diaphysis
    • Endosteal scalloping
    • Intra-lesional calcification in adults
      • Especially long bones
    • Annular, comma-shaped, punctate
    • Calcification often absent in hand lesions
    • Thin sclerotic rim
    • Bone expansion
      • Due to lack of remodelling of metaphysis
      • Not due to expansion by tumour
    • No periosteal reaction
    • Often appears to travel down into diaphysis as physis grows away from it
  • Bone Scan
    • Usually ↑ uptake (↑ bone turnover)

Pathology

Gross

  • Lobulated translucent cartilage which may have calcification
  • Pearly-white tissue

Microscopic

  • Bland hyaline cartilage matrix with chondrocytes in lacunae
  • Chondrocytes have small dark nuclei & in sparse numbers
  • No obvious cellular atypia
  • Hand lesions tend to look more hypercellular & pleomorphic
  • Calcification common
  • No invasive infiltration of marrow spaces (cf. Chondrosarcoma)

Differential Diagnosis

  • Long Bone with intralesional calcification
    • Medullary Bone Infarct (serpiginous calcification)
    • Chondrosarcoma
  • Phalanx
    • Epidermoid Inclusion Cyst
    • Glomus Tumour
      • 50% subungual
      • Triad of severe pain, tenderness, cold sensitivity
  • At End of Bone
    • GCT

Treatment

  • If asymptomatic then observation adequate
  • If pain or pathological fracture
    • Intralesional curettage & grafting will allow resolution
    • Recurrence high & seeding to soft tissues can occur
  • Complications
    • Usually 1A lesions
  • Malignant transformation rare
    • < 1% of cases
    • Usually seen in
      • Central lesions – pelvis & scapula
      • Diaphyseal lesions (ie. older lesions)
    • Considered if
      • Onset of pain in absence of pathological fracture
      • Enlargement of lesion
      • Cortical erosion
      • Thickening or destruction of cortex
      • Presence of soft tissue mass

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