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fibrous cortical defect/non-ossifying fibroma group of bone tumors

Monday 4 January 2010

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.

Radiological differential diagnosis

Although the radiographic findings usually are pathognomonic, the differential diagnosis includes the following:

- chondromyxoid fibroma;
- fibrous dysplasia, particularly if lesions are multiple and polyostotic (in comparison, fibrous dysplasia has a more central and unilateral location and more of a ground-glass appearance);
- osteoid osteoma (typically has a central nidus);
- bone abscess;
- periosteal chondroma;
- avulsive cortical irregularity
- periosteal desmoid fibromatosis (saucerlike radiolucent defect in the cortex with adjacent sclerosis and periostitis);
- desmoplastic fibroma
- cortical avulsive injury

Reports of soft-tissue desmoid fibromatosis or desmoplastic fibromas of bone have been noted only when the fibrous tissue in these lesions is examined at biopsy.

Although much less common, consider giant cell tumor and aneurysmal bone cysts in the differential diagnosis of a large lobulated fibroxanthoma at radiographic study. However, both of these lesions are clearly distinguished at CT or MRI.

A herniation pit also has been described in the differential diagnosis of fibrous cortical defect (FCD).

The cortical avulsive injury that occurs in adolescents has been noted more frequently. It often was and still is confused with FCD. At histologic evaluation, cortical avulsive injury has a nonspecific fibrous appearance with intermixed spicules of bone and healthy osteoblasts. Later findings indicated that the histologic features of the cortical avulsive lesion (characteristically located at the insertion of the tendon at the posteromedial cortex of the distal femur) included those of healthy tendon and interspersed bone and cartilage; therefore, this lesion is separate from FCD and secondary to repetitive trauma rather than being a true developmental defect.

Links

- emedicine.medscape.com

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