Tumor biology and incidence

  • Benign lesion of cortical bone located in metaphysis
  • Generally latent
  • Common lesions; many go without diagnosis
    • Approximately 5% of all investigated benign bone tumors
    • Actual incidence probably much higher as many are asymptomatic

Age

  • Most often diagnosed in children ages 4-8 years
  • Symptomatic almost exclusively in children; rarely symptomatic after cessation of skeletal growth

Gender

Males are more commonly affected than females

Presentation

  • Usually asymptomatic, incidental finding
  • May present with a pathologic fracture or pain

Physical findings

Usually none

Plain films

Site
  • Distal femur and tibia
  • Eccentric and usually confined to cortex
Size

Usually less than 4 cm

Tumor effect on bone

Radiolucent, elliptical lesion withinmetaphyseal or metaphyseal-diaphyseal cortex of long bone

Bone response to tumor
  • Sharply demarcated by thin sclerotic margin
  • Metaphyseal neo-cortical response seen when lesion grows into metaphysis
Cortex

Lesion confined to cortex

Soft tissue mass

None

Bone scan

May demonstrate increased uptake due to bone remodeling

Differential diagnosis

  • Infection
  • Chondromyxoid fibroma
  • Fibrous histiocytoma, non-ossifying fibroma of bone

Natural history

  • Most heal spontaneously with progressive ossification
  • Lesion that continues to enlarge and then encroaches on medullary cavity is designated a non-ossifying fibroma

Pathology

  • Gross: Cortex is replaced with fibrous tissue with granular appearance; may have yellow areas
  • Microscopic: Spindle cell proliferation with storiform arrangement
  • Multinucleated giant cells and abundant iron
  • Foamy histiocytes may be seen
  • Usually no bone formation

Diagnosis and treatment

  • Plain x-rays usually diagnostic; biopsy rarely indicated
  • Observation only
    • Repeat radiographs at 3 to 6 month intervals for approximately 1 year if the lesion is atypical
    • Lesions usually heal spontaneously
  • Treatment for the progressive painful lesion is curettage and bone graft