Basics
Description
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NOF is a common developmental abnormality in children and adolescents with open physes; it is not seen in adults.
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Despite the name, this condition mineralizes and disappears with skeletal maturity.
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When the lesion is very small, it is called a fibrous cortical defect.
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Occurs eccentrically in the metaphyses of long bones, most commonly in the distal femur, proximal tibia, or distal tibia
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The lesion is seen in children and adolescents, but not in adults.
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Staging (as with other benign lesions):
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Stage 1: Latent (~96%)
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Stage 2: Active (~2-3%)
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Stage 3: Aggressive (<1%)
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Natural history:
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Active stage 2 during childhood
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Becoming latent stage 1 at skeletal maturation
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Synonyms: Benign metaphyseal cortical defect; Metaphyseal fibrous defect; Benign fibrous histiocytoma; Fibrous xanthoma
Epidemiology
A common skeletal lesion
Incidence
Estimated to occur in 35% of healthy children with open physes
Etiology
The cause is hypothesized to be a focal area of increased periosteal resorption during growth.
Associated Conditions
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NF:
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NOF-appearing lesions may be found (~5%).
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Rare, congenital disorder
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Multiple NOFs (widespread and symmetric)
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Cafe-au-lait pigmentation
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Nonskeletal abnormalities
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Mental retardation
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Diagnosis
Signs and Symptoms
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Most lesions are asymptomatic and are found incidentally on radiographs.
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Occasionally, the condition is painful if a pathologic fracture occurs through the lesion or if such a fracture is impending.
Physical Exam
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Usually, the lesion is nontender.
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No swelling or tenderness should be present with weightbearing, unless a fracture is impending.
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NOF-like lesions may occur in NF.
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Jaffe-Campanacci syndrome
Tests
Imaging
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On plain radiographs, a lytic (radiolucent) lesion is seen eccentrically in the metaphyses of long bones (usually the distal femur, proximal tibia, or distal tibia).
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Based in the cortex
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Overlying cortex if thinned
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Surrounded by a scalloped, reactive rim of sclerotic (radiopaque) bone
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Often appears multiloculated, producing a bubbling appearance
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Ranges in size from a few millimeters to a few centimeters
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Usually solitary
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If a bone scan is obtained, the lesion will appear hot early on from the reactive rim of bone.
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As the lesion heals, the bone scan will become normal.
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Pathological Findings
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The lesion is filled with fibrous connective tissue arranged in a whirled, starry night pattern.
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Also seen are multinucleated giant cells, foam-filled histiocytes, and hemosiderin pigmentation.
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Cystic spaces are not typical.
Differential Diagnosis
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Chondromyxoid fibroma
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Fibrous dysplasia
Treatment
General Measures
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In general, full, unrestricted activity is allowed.
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If weightbearing pain develops, AP and lateral radiographs should be obtained to look for stress fractures.
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MRI is effective in detecting stress fractures.
Medication
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The treatment for large lesions is radiographic monitoring according to the physician’s judgment because the lesion is self-healing at skeletal maturity.
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Patients with large lesions should be seen every 6 months.
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This monitoring may continue until growth is complete.
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If >50% of the cortex is involved, and the patient is symptomatic (pain), a pathologic fracture is possible.
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In this case, treatment is surgery with curettage and bone grafting.
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If the lesion is small and asymptomatic (<25% of the width of the cortex), no monitoring is needed.
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No restrictions are placed on activity unless a pathologic fracture is impending (>50% of the cortex is involved in a symptomatic child), in which case the child should be nonweightbearing or have protected weightbearing on the affected extremity.
Surgery
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For impending pathologic fracture, curettage (scraping the lesion) followed by bone grafting (placing bone graft into the lesion) should be performed.
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Internal fixation usually is not necessary.
Follow-up
Prognosis
All these lesions are self-healing at skeletal maturity.
Complications
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Pathologic fracture is seen rarely.
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Pathologic fractures usually occur only in lesions involving >50% of the cortex in symptomatic patients or in patients who have had severe trauma.
Patient Monitoring
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Serial radiography:
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AP and lateral views of the affected part
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Miscellaneous
Codes
ICD9-CM
213.9 Fibrous cortical defect
Patient Teaching
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Tell children that they must report pain or limp to their parents.
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Reassure the child and parents regarding the benign nature of the lesion, the natural course of self-healing, and the prevalence of the lesion in healthy children (35%).
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If the lesion is small, no follow-up is needed.
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If it is large, follow-up should be obtained every 6-12 months.
FAQ
Q: If a child has a large NOF and is completely asymptomatic, is protected weightbearing or surgery necessary?
A: In general, if the child is completely asymptomatic, protected weightbearing is not necessary. A small risk of fracture is likely with trauma. Surgery is not necessary.
Q: What are the disadvantages of surgery?
A: A major disadvantage is the scar and the need for protected weightbearing for 3-6 months after surgery.
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