Pathophysiology
Both non-ossifying fibroma (fibroxanthomas) and fibrous cortical defects (FCDs) are composed of spindle-shaped fibroblasts that are oriented in a cartwheel or storiform whorled pattern, with scattered giant cells (osteoclastlike multinucleated cells), foam (xanthoma) cells, and small amounts of collagen.
Foam cells occur in 30-50% of cases and are more common in older lesions. Abundant hemosiderin in the cytoplasm of the fibroblast cells has been noted; cholesterol crystals also have been identified. At histologic analysis, no mitosis or pleomorphism is present to suggest malignancy.
Frequency
United States: The exact incidence is unknown; however, 30-40% of all children may have one or more of these lesions at one time. In one study, Caffey reported a frequency of 36% in children.
International: No definite distinction has been reported between the frequency in the United States and that worldwide.
Mortality/Morbidity
Because non-ossifying fibroma (fibroxanthoma) and fibrous cortical defect are nonaggressive fibrous lesions of bone, no increase in morbidity or mortality is noted with either one.
Race
No racial predilection exists.
Sex
In the literature, a slight male predominance is reported. Fibroxanthomas occur 2 times more frequently in males than in females. Also, fibrous cortical defects have been reported in males twice as often as in females; however, 1 study revealed an 11:3 ratio of the incidence in males versus females.
Age
Both lesions occur in the developing skeleton. Fibrous cortical defects (FCDs) occur in younger patients, with presentation in those aged 4-8 years. Usually, FCDs are incidental findings on radiographs that are obtained for indications other than the evaluation of FCD.
Peak occurrence is in those aged 10-15 years, with decreasing incidence in 13- to 14-year-old adolescents. The overall age range of patients is reported to be 3-20 years.
FCDs never appear for the first time in adults, and they are thought to have persisted from childhood if they are present in adults.
Fibroxanthomas typically occur in children and adolescents; 70% occur in teenagers. The age range of patients with fibroxanthomas is reported to be 3-42 years.
Anatomy
Approximately 90% of cases of both lesions involve the tubular long bones.
Common sites include the femur (most commonly the distal femoral metaphysis [38%]), the proximal and distal tibia (43%), and the knee (55%); most lesions occur around the knee.
The tibial diaphysis is involved in only 10% of cases. The fibula is affected in 8-10% of cases, as noted in one series at the Armed Forces Institute of Pathology (AFIP). Both fibroxanthoma and fibrous cortical defects (FCDs) are uncommon in the upper extremity; however, of those reported in the literature, 8% were in the humerus, and both radial and ulnar lesions were rare. Less common sites include the innominate bone, clavicle, skull, scapula, mandible, and small bones of the hands and feet.
Typically, both lesions are metaphyseal and arise close to the physeal plate. The FCD arises within the cortex, whereas the fibroxanthoma arises eccentrically within the medullary cavity. Both lesions usually arise from the posterior wall of the tubular bone, and involvement of the medial rather than lateral osseous surface is characteristic. With healthy growth of the osseous skeleton, the lesions extend toward the shaft, and if they do not involute and disappear, they may extend into the diaphysis. An epiphyseal location is distinctly uncommon and has been reported only in unusual cases of multifocal lesions. Both lesions are more commonly solitary, and they can occur in similar locations.
Multifocal lesions in one or more bones can occur with FCDs; however, multifocal fibroxanthomas are less common and, if present, have other clinical manifestations (see Clinical Details). Moser et al described lesions in clusters in the same bone, at opposite ends of the same bone, and at opposite sides of the joints.
Presentation
Typically, fibrous cortical defects (FCDs) are asymptomatic and are detected only incidentally on radiographs obtained for reasons other than the evaluation of FCD. Fibroxanthomas also are characteristically asymptomatic; however, in larger lesions, mild pain may occur secondary to radiographically undetected microfractures that may eventually lead to painful and radiographically evident pathologic fractures.12 Although they are most commonly solitary lesions, multiple lesions have been described. Rare reports of multiple fibroxanthomas in patients with neurofibromatosis (5%) exist in the literature.
The presence of extraskeletal congenital anomalies (eg, café-au-lait spots, mental retardation, hypogonadism or cryptorchidism, ocular abnormality, cardiovascular malformations) in association with multiple nonossifying fibroxanthomas constitute the clinical and radiologic spectrum known as Jaffe-Campanacci syndrome, which was first reported in 1983.13,14 In one series, Moser et al also noted that the coexistent osteochondromas can be present.1
Preferred Examination
Plain radiographic findings are virtually diagnostic of both fibrous cortical defects and nonossifying fibromas; most of these lesions have a characteristic location and appearance. If a discrepancy in appearance or age or an atypical associated symptom is present, advanced imaging (usually computed tomography [CT] or magnetic resonance imaging [MRI]) can be performed.
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