Fibrous dysplasia is a noninherited bone disease in which abnormal differentiation of osteoblasts leads to replacement of normal marrow and cancellous bone by immature bone with fibrous stroma. Monostotic fibrous dysplasia accounts for 28% in the ribs. It is often asymptomatic and incidentally detected on radiographs. As with many bone abnormalities, it can be superimposed by the formation of aneurysmal bone cysts. We report a case of a 70-year-old lady who presented with swelling on the chest wall of 20-ear duration and sudden increase in size for 8 months. Radiologically, X-ray and CT scan showed an expansible lesion of the medullary cavity with a ground-glass centre and thinning of cortex of the 5th rib. The resected lesion was a firm, well-defined solid, grey-white expansile mass replacing the medullary cavity. Histopathologically, benign fibrous spindle areas with disorganized irregular bony trabeculae were seen. Hemorrhagic spaces lined by osteoclast-like multinucleated giant cells were also noted. The diagnosis was fibrous dysplasia with aneurysmal bone cyst changes. Although fibrous dysplasia with aneurysmal bone cyst is rare, it should be taken into account in differential diagnosis of the rapidly growing solitary rib lesion.
Fibrous dysplasia (FD) is a noninherited developmental bone disorder in which abnormal differentiation of osteoblasts lead to replacement of normal marrow and cancellous bone by immature woven bone with fibrous stroma [
A 70-year-old lady came with sudden increase in size of the swelling of 20-year duration on the left side of chest since 8 months. Radiologically, X-ray and computed tomography (CT) scan showed lobulated, expansile intramedullary lesion with a ground-glass centre and thinning of the cortex arising from the anterolateral aspect of left the 5th rib (Figures
(a) X-ray and (b) CT scan-lobulated, expansile, intramedullary lesion (arrow) with ground-glass centre and thinning of the cortex arising from the anterolateral aspect of the left 5th rib.
Gross: firm, well defined solid grey white expansile mass replacing the medullary cavity of the rib (arrow) with areas of hemorrhage.
The specimen X-ray ((a) and (b)) displaying the intact lesion with no soft tissue extension.
Microscopy, (a) “Chinese alphabet” spicules of woven bone (arrows) separated by abundant fibrous stroma (H&E, 20x). (b) No atypia of stromal cells (H&E, 100x).
Microscopy, (a) FD (left) With ABC (right) changes—hemorrhagic spaces lined by osteoclast-like multinucleated giant cells (arrows) (H&E, 20x). (b) Osteoclast-like multinucleated giant cells lining hemorrhagic spaces (arrows) (H&E, 100x). (c) Intact periosteum with host lamellar bone and no soft tissue extension (H&E, 20x).
Fibrous dysplasia (FD) is a benign skeletal disorder, described by Lichtenstein in 1938 and Lichtenstein and Jaffe in 1942. It accounts for 0.8% of primary and 7% of benign bone tumors. FD is monostotic form in 70–80% of cases and polyostotic in 20–30% of cases. Wide age range presentation between 10 and 70 years, with 75% of patients presenting before the age of 30 years [
The gross appearance of FD is a firm solid grey-white mass replacing the medullary cavity and surrounded by cortical bone. Histopathologically, the lesion appears well circumscribed and sharply delineated by the host lamellar bone. It is composed of uniformly cellular fibrous tissue containing a proliferation of bland and uniform spindle cells with sparse mitotic activity. Scattered across the fibrous matrix are lamellae or rounded nests of woven bone without significant osteoblastic rimming. There is some morphologic variability in the woven bone spicules. The classic, most commonly seen pattern is that of curvilinear, “Chinese alphabet” spicules of woven bone separated by abundant fibrous stroma. Less commonly, the woven bone may be deposited either in sclerotic, interconnected lamellae, cementoid bodies, or in orderly and parallel spicules [
The imaging features of FD are characteristic, although not specific, and depend on the underlying histopathology of a given lesion. Radiographs show unilateral fusiform enlargement of medulla, deformity with cortical thickening, and increased trabeculation. A characteristic “ground-glass” appearance is created by the mixture of woven bone and fibrous components that replace the medullary space. The degree of haziness directly correlates with its underlying histopathology. More radiolucent lesions are composed of predominantly fibrous elements, whereas more radiopaque lesions contain a greater proportion of woven bone [
Sudden increase in development of already existing FD will be either due to superimposed ABC or malignant transformation [
Malignant transformation with rapid expansion of the bone has been reported in about 0.5% of patients with monostotic FD but in nearly 4% of those with McCune-Albright syndrome. It may develop after irradiation of the involved bones. Malignant transformation is most common to osteosarcoma, although fibrosarcoma, chondrosarcoma, or malignant fibrous histiocytoma noted [
Treatment of FD for asymptomatic and stable lesions should be simply monitored. Surgery is indicated only for confirmatory biopsy, correction of deformity, failure of nonsurgical therapy, prevention of pathologic changes, and/or eradication of symptomatic lesions. When surgery is not possible and in the polyostotic form, bisphosphonate therapy is indicated with positive effects exerted on bony density and the reduction of pain. However, a surgical management is preferred for FD of the rib location as simple surveillance can raise the difficult problem of differential diagnosis with malignant tumors [
Our case thus gave rise to sudden increase in development of an already existing FD with altered hemodynamic changes by the ABC, clinically presented as malignant lesion.
The development of ABC in FD will hasten the course of clinical presentation. FD with ABC should be taken into account in differential diagnosis of the rapidly growing solitary rib lesion. In symptomatic monostotic FD of ribs, the involved segment of bone should beexcised to rule out malignancy and for relief from symptoms. Knowledge of the various appearances, complications, and associations of FD is important to ensure the accurate diagnosis and appropriate management in ribs location.