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Fibrous Cortical Defect

  • AKA Non-ossifying fibroma

Definition

  • Benign well-circumscribed eccentric solitary lesion in metaphysis of long bone in children
  • Multiple lesions rare
  • Lesions seen in children called fibrous cortical defect
  • Lesions seen in adults traditionally called non-ossifying fibroma

Epidemiology

  • 35% incidence in normal children on radiological surveys
  • Most common skeletal lesion
  • Most common cause of pathological fracture in children
  • Peak age of 15 years
  • Gender
    • M:F – 1.5:1
  • Localized defect in cortex of long bone
    • Failure of bone to form
    • Self limiting
    • Usually ossify by early adulthood
  • Location
    • 50% about the knee
    • Distal tibia
    • Proximal femur
    • Proximal humerus
    • Lesions usually regress spontaneously

Clinical Features

  • Most incidental findings on XR & asymptomatic
  • Rarely have pathological fracture

Radiological

  • Cortical eccentric position in metaphysis (cf. Fibrous Dysplasia)
  • Well-demarcated central lucent zones surrounded by scalloped sclerotic margins
  • Usually < 1/3 diameter of bone
  • May be elongated in longitudinal axis of bone
  • Will migrate away from the epiphysis with growth
  • As regresses replaced with residual sclerosis

Pathology

Gross

  • Soft, friable, yellow or brown tissue

Microscopic

  • Cellular tissue
  • Unremarkable spindle cells in interlacing or whorled pattern
  • Interspersed with multinucleated giant cells & histiocytes
  • May be similar to GCT

Differential Diagnosis

Treatment

  • Usually observation only
    • Serial observation (XR 4/12 for 1st year then yearly)
    • Usually don't require biopsy
    • Biopsy if uncertain
  • If > 50% of diameter of bone
    • Curettage & bone graft
  • If pathological fracture
    • Treat closed if possible
    • Fracture heals in normal length of time
    • Lesion may heal with fracture union
    • If persists then curettage & graft
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