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

• Fibrous Dysplasia
• Eosinophilic Granuloma
• Ewing’s Sarcoma
• Adamantinoma

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