summary Non-Ossifying Fibromas are benign fibrogenic lesions that result from dysfunctional ossification that are most commonly found in the metaphysis of long bones. Patients typically present between the ages of 5 and 15 with an asymptomatic lesion discovered incidentally on radiographs. Diagnosis is made on radiographs with a characteristic metaphyseal eccentric "bubbly" lytic lesion surrounded by a sclerotic rim. Treatment is observation as most lesions resolve spontaneously. Epidemiology Incidence occurs in 30-40% of skeletally immature children Demographics more common in males (2:1) common in children 5-15 years old Anatomic location metaphysis of long bones 80% in lower extremity distal femur > proximal tibia > distal tibia uncommon in proximal femur, proximal humerus Etiology Mechanism non-ossifying fibroma (NOF) is a benign fibrogenic lesion that is related to dysfunctional ossification one of the most common benign bone tumors in childhood (with osteochondroma) other names metaphyseal fibrous defect nonosteogenic fibroma cortical desmoid fibrous cortical defect fibromatosis fibroxanthoma Pathophysiology possibly due to abnormal osteoclastic resorption at the subperiosteal level during remodeling of the metaphysis Associated conditions Jaffe-Campanacci syndrome congenital syndrome of multiple non-ossifying fibromas and cafe au lait pigmentation mental retardation heart, eyes, gonads involved neurofibromatosis familial multifocal NOF ABC Presentation Symptoms asymptomatic usually found incidentally may present with pathologic fracture Imaging Radiographs diagnostic metaphyseal eccentric "bubbly" lytic lesion surrounded by sclerotic rim cortex may be expanded and thin length > width as bone grows migrates to diaphysis lesions enlarge (1-7cm) as patient approaches skeletal maturity, lesions become sclerotic avulsion of adductor magnus insertion in the posteromedial aspect of the distal femur may produce a similar looking lesion CT quantitative CT shown to be useful in predicting fracture risk Studies Histology classic characteristics are fibroblastic spindle cells in whirled or storiform pattern (helicopter in wheat field) fibroblastic connective tissue background numerous lipophages and giant cells hemosiderin pigmentation occasional ABC component Differential Giant cell tumor painful rare in skeletally immature no mineralization Osteosarcoma painful irregular zone of bony destruction with less defined zone of transition periosteal reaction mineralized soft tissue mass Differential of non-Ossifying Fibroma "Bubbly" lytic lesion on xray Hemosiderin seen on Histology Treatment is Observation alone NOF o o o ABC o UBC o PVNS o Fibrous dysplasia o Enchondroma o Osteochondroma o Eosinophillic granuloma o Paget's o Treatment Nonoperative observation indications first line of treatment most lesions resolve spontaneously and progressively reossify as child enters 2nd and 3rd decade of life technique radiographs at 6 and 12 months, then annually until reossified casting indication pathologic fracture can be treated as per the fracture alone (long leg casting for distal femur pathologic fx) Operative curettage and bone grafting indication symptomatic and large lesion (> 50-75% cortical involvement) increased risk of fracture shown on quantitative CT Complications Pathologic fracture incidence 90% occur in the lower extremity 50% occur in the distal tibia risk factors >50% involvement of transverse diameter >33mm length in weight-bearing bones (femur and tibia) treatment cast immobilization indications nondisplaced fractures Prognosis Usually spontaneously resolves No malignant or metastatic potential