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| IMAGE QUIZ ARCHIVE | ||||||
| Image Quiz | ||
| Leg Pain and Swelling in an Adult1 (continued) | ||
| Answer: Fibrous dysplasia of the proximal part of the fibula. | ||
 Fig. 4-A |
 Fig. 4-B |
For larger view, click on image |
| Figs. 4-A and 4-B. Low-power photomicrograph of the biopsy specimen (Fig. 4-A), demonstrating thick bone trabeculae in a dense hypercellular stroma (hematoxylin and eosin, original magnification; ×10) and foci (Fig. 4-B) resembling a cementifying variant of fibrous dysplasia (hematoxylin and eosin; original magnification, ×20). | ||
| Discussion | ||
| Fibrous dysplasia has been described as a dysplastic anomaly of bone-forming mesenchymal tissue1. Morphologically and histologically, it represents a dysplastic disorder of bone characterized by solitary or multifocal polyostotic intramedullary lesions composed of proliferations of fibroblast-like spindle cells with a characteristic whorled pattern in which trabeculae of immature woven bone (typically not bordered by palisading osteoblasts) may be present. | ||
| In 1937, Albright et al. reported a syndrome in five patients who had multiple, predominantly unilateral bone lesions involving the digits and the extremities, areas of skin pigmentation, and endocrine dysfunction2. In 1942, Lichtenstein and Jaffe described the entity and named it fibrous dysplasia of bone3. | ||
| Fibrous dysplasia occurs with equal prevalence among boys and girls and usually presents during the first three decades of life (approximately 70% of cases)4. Involvement of the long bones, the ribs, and the skull is most frequently reported, although any bone may be affected5,6. Fibrous dysplasia tends to affect the metaphyseal and diaphyseal regions of long bones. Of all the long bones, the proximal part of the femur is the most commonly reported site of involvement4. | ||
| Fibrous dysplasia may be monostotic or polyostotic. Patients are usually asymptomatic, although pathologic fractures can occur. In the polyostotic form, depending on the extent of involvement, the patient usually presents with a limp, extremity pain, or pathologic fracture. The extraskeletal sign most frequently noted in both forms is hyperpigmentation of the skin associated with café-au-lait spots7. In patients with fibrous dysplasia, these light brown areas of pigmentation are variable in size and have irregular margins. In contrast, in patients with neurofibromatosis, the skin lesions have smooth borders. Another manifestation of fibrous dysplasia is the McCune-Albright variant, a triad of polyostotic fibrous dysplasia, abnormal skin pigmentation, and precocious puberty7. Other associated endocrinopathies may be seen with McCune-Albright syndrome, including hyperthyroidism, Cushing's disease, acromegaly, hyperparathyroidism, and diabetes mellitus. The rarest variant of fibrous dysplasia is Mazabraud syndrome, which typically has a polyostotic presentation and soft-tissue myxomas8,9. | ||
| The diagnosis usually is made on the basis of history, physical examination, and imaging studies. The woven bone that characterizes fibrous dysplasia often produces a varied radiographic density, classically described as "ground-glass matrix."10 There may be associated areas of medullary expansion and focal cortical thinning. The lesion may have sclerotic borders, and cystic lesions also may be present. Bone scans or skeletal surveys are useful to identify or exclude polyostotic forms of the disease. Computed tomographic scanning helps to define the extent of involvement, especially with regard to craniofacial disease6. Magnetic resonance imaging is useful for defining the anatomy and extent of the lesion, especially when the radiographic features are atypical. | ||
| Histologically, the small, irregular-shaped bone trabeculae appear within a collagenous fiber matrix. The irregularity of these trabeculae has been compared to both "Chinese letters" and "alphabet soup."7 Osteoblastic rimming, which is characteristic of reactive or neoplastic bone, is usually absent. However, osteoblasts are occasionally identified in close proximity to the osseous trabeculae. The amount of woven bone is variable and, in some cases, fibrous stroma is predominant. The woven bone never matures into lamellar bone, suggesting that fibrous dysplasia represents a maturation defect wherein the process of bone formation is arrested at an early woven-bone stage of skeletal differentiation that resembles membranous ossification. This poorly mineralized tissue gradually replaces normal bone by a process of metaplasia, thereby weakening the overall integrity of the involved bone. Occasionally, lesions of fibrous dysplasia show calcified spherules similar to those seen with cementifying fibromas. Focal areas of hyaline cartilage and cystic areas may also be present. | ||
| Lesions with abundant bone elements appear to be more radiopaque, whereas lesions with a predominance of fibrous tissue appear to be more radiolucent. Mild cortical expansion has been noted in affected bones, especially in flat bones and in major long tubular bones1. When a fibrous dysplasia lesion has an aneurysmal bone cyst component, it can appear to be more aggressive and/or destructive on imaging studies. An aneurysmal bone cyst in association with fibrous dysplasia, although rare, has been reported11,12. Cystic degeneration in association with fibrous dysplasia is also rare and has been reported to occur in the craniofacial bones13. A predominantly lytic appearance or enlargement of fibrous dysplasia has been suggested to indicate cystic degeneration or malignant transformation14,15. Cystic fibrous dysplasia mimicking giant cell tumor in long bones has also been reported16. | ||
| We believe that the current case represents cystic degeneration in an existing fibrous dysplasia lesion rather than an aneurysmal bone cyst. Histologically, the lesion represented a variation in the spectrum of fibrous dysplasia. The lesion had a notably more hypercellular stroma with thicker seams of osteoid that were more densely calcified and with foci resembling cementifying fibrous dysplasia and areas of cystic degeneration. It lacked any cytologic atypia, increased mitotic activity, or necrosis. | ||
| Upon diagnosis, surgical excision of the lesion was offered as a therapeutic intervention. The proximal part of the fibula was excised with the lesion, en masse, with a cuff of normal bone. The patient has had no recurrence at the latest follow-up, two years after the operation. | ||
| *In support of their research or preparation of this manuscript, one or more of the authors received grants or outside funding from Stryker. In addition, one or more of the authors received payments or other benefits or a commitment or agreement to provide such benefits from a commercial entity (Stryker). No commercial entity paid or directed, or agreed to pay or direct, any benefits to any research fund, foundation, educational institution, or other charitable or nonprofit organization with which the authors are affiliated or associated. | ||
| Reference | ||
1. Dorfman HD, Czerniak B. Bone tumors. St Louis: Mosby; 1998. Fibroosseous lesions; p 441-91. |
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