Practice Essentials
Fibrous cortical defect (FCD; also referred to as nonossifying fibroma [NOF] or nonosteogenic fibroma) was first described by Phemister in 1929. Sontag and Pyle reported a radiologic description in 1941, [1] and in 1942, Jaffe and Lichtenstein described clinical and anatomic aspects and the natural history. [2]
FCD probably is the most frequent bony lesion in children, occurring in as many as 30-40%. [3] It is most common in adolescents. The term FCD was coined to describe the smaller variety of NOF [4] ; for a lesion large enough to encroach on the medullary canal, the term NOF has commonly been used. However, no histologic difference exists between these lesions. The authors believe that FCD and NOF should be considered the same entity, and in this article, the two terms are used interchangeably (except where cited studies distinguish between them). These lesions are, in fact, developmental abnormalities, as opposed to benign neoplasms.
FCD usually is an incidental finding on radiographs. Always benign, it may result in pathologic fracture, though this is is a rare first presentation. [5] These lesions can exist in multiple sites. FCD may be difficult to diagnose in the presence of pain or swelling of soft tissues. It also can be confused with a more aggressive lesion [6, 7] ; therefore, biopsy may be necessary.
The characteristic location and appearance are usually suggestive of a benign lesion and are often pathognomonic; thus, no further action is necessary unless a pathologic fracture has occurred or risk of fracture is high. Fractures and impending fractures are indications for surgical intervention. Association with other bone lesions, such as aneurysmal bone cyst, is rare. [2, 4, 8, 9, 10, 11]
Pathophysiology
The average duration of FCD is in the range of 29-52 months, after which period the lesion spontaneously resolves. FCD may be present during childhood, but lesions tend to disappear in adolescence.
Etiology
The etiology of FCD remains obscure. FCD is a proliferation of benign fibrous tissue, possibly developing as a result of periosteal injury or secondary to abnormalities at the epiphyseal plate. Others postulate that FCD is related to the normal cutback phenomenon seen in maturing physeal plates. Progression of this lesion introduces abnormal tissue into the metaphyseal cortex.
Epidemiology
FCD has been reported to account for 5% of benign tumoral lesions of bone. It has been argued that the true incidence is more likely to be on the order of 30% or higher, but because FCD is asymptomatic in most patients, most lesions are never identified.
Sontag and Pyle identified this lesion in 54% of boys and 22% of girls in a series of 200 healthy children. [3, 12] Collier et al, in a longitudinal radiographic study of 252 asymptomatic children screened for benign bone tumors at a median age of 8 years, identified 19 NOFs in the 33 patients found to have tumors. [13]
An epidemiologic study from Japan assessed 6222 children (3567 boys, 2455 girls) aged 5-15 years who had undergone standard anteroposterior and lateral radiography of the knee to determine the prevalence of NOF and FCD and evaluate the association between lesion size and pain. [14] There were 143 NOF cases (prevalence, 2.3%) and 437 FCD cases (prevalence, 7.0%), figures lower than those reported in previous studies. The average lesion size was 22.1 mm for NOF (range, 4-102 mm) and 13.2 mm for FCD (range, 5-21 mm). Lesion size was not associated with spontaneous pain in either NOF or FCD.
These lesions occur in multiple sites in approximately 50% of patients. FCD is rare in children younger than 2 years and is most common in adolescents. Collier et al found NOF to have a bimodal distribution, with one peak occurring at the age of 5 years and the other after skeletal maturity. [13]
Prognosis
The rarity of FCDs in adults confirms that these lesions regress with time. The prognosis is excellent in those unusual cases where patients require curettage and bone grafting. [15]
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Plain radiograph demonstrating multiple fibrous cortical defects in multiple bones.
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Plain radiograph of fibrous cortical defect of the proximal tibia.
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Lateral radiograph demonstrating a solitary fibrous cortical defect in the proximal tibia.
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CT scan of the fibrous cortical defect shown in the plain radiographs in Images 2-3; note the cortical location and the sclerotic rim around the central lucency.
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Methylene diphosphonate technetium bone scan of the fibrous cortical defect in Images 2-4; uptake is minimally increased at the site of the lesion.
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Histologic section of a fibrous cortical defect demonstrating a bland fibrous stroma in the absence of nuclear atypia or mitoses; a few giant cells are scattered within the stroma.
