Pathogenesis of aneurysmal bone cyst. Relationship between the aneurysmal bone cyst and fibrous dysplasia of bone.
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UNLABELLED: Deposition, mineralization, and resorption of FD bone compared with unaffected bone from FD patients was investigated in iliac crest biopsy specimens from 13 patients. Compared with unaffected bone, lesional FD bone seemed to be very sensitive to the effects of PTH and renal phosphate wasting, which respectively bring about hyperparathyroid or osteomalacic changes in the lesional bone. INTRODUCTION: Fibrous dysplasia is a genetic noninherited disease caused by activating mutations of the GNAS1 gene, resulting in the deposition of qualitatively abnormal bone and marrow. This study was designed to learn more about the local processes of bone deposition, mineralization, and resorption within lesional fibrous dysplasia (FD) bone compared with unaffected bone of FD patients. METHODS: Histology, histomorphometry, and quantitative back-scattered electron imaging (qBSE) analysis was conducted on affected and unaffected biopsy specimens from 13 patients and correlated to markers of bone metabolism. RESULTS AND CONCLUSIONS: There was a marked excess of unmineralized osteoid with a nonlamellar structure and a reduced mineral content in mineralized bone within FD lesions (p < 0.001). A negative correlation (p = 0.05) between osteoid thickness (O.Th) and renal tubular phosphate reabsorption (measured as TmP/GFR) was observed for lesional bone, but not for unaffected bone, in which no histological or histomorphometric evidence of osteomalacia was observed in patients with renal phosphate wasting. Histological and histomorphometric evidence of increased bone resorption was variable in lesional bone and correlated with serum levels of parathyroid hormone (PTH). Hyperparathyroidism-related histological changes were observed in fibrous dysplastic bone, but not in the unaffected bone, of patients with elevated serum PTH secondary to vitamin D deficiency. Our data indicate that, compared with unaffected bone, lesional FD bone is very sensitive to the effects of PTH and renal phosphate wasting, which, respectively, bring about hyperparathyroid or osteomalacic changes in the lesional bone. Osteomalacic and hyperparathyroid changes, which emanate from distinct metabolic derangements (which superimpose on the local effects of GNAS1 mutations in bone), influence, in turn, the severity and type of skeletal morbidity in FD.
McCune-Albright syndrome (MAS) is a sporadic disease characterized by fibrous bone dysplasia, café-au-lait spots and hyperfunctional endocrinopathies. We report a 2.5-year-old child with MAS with an early and nonclassic onset. He was admitted to our attention for frequent fractures without clinical signs of endocrinopathies, found to have asymptomatic, nonautoimmune hyperthyroidism. The diagnosis of MAS was based on RX and MR imaging associated with hyperthyroidism. It is not clear if there was a correlation between the severity of bone disease and the presence of thyroid disorder. At the moment no standard treatment exists for bone fibrous dysplasia and hyperthyroidism in children before the age of 6 years.
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Eight cases of fibrous dysplasia were evaluated by electron microscopy and the findings were correlated with the light microscopy. Fibroblasts and myofibroblasts were the cells seen in the fibrous component. The osseous component consisted of immature woven bone trabeculae lined by abnormal osteoblasts with a fibroblastlike appearance. The cartilaginous component resembled hyaline cartilage. The process of mineralization of both osseous and cartilaginous tissues appeared similar to normal bone and cartilage. In fibrous dysplasia there is a slow turnover of bone, and this correlates well with the flattened shape of the bone-lining cells. When compared with normal ossification, the process of bone formation appears to be arrested after an early stage resembling membranous ossification. It is possible that the abnormal osteoblastic maturation of the bone-forming mesenchyme is one of the most important alterations of this condition.
monostotic. Although most patients had a conductive hearing loss, 17% of patients demonstrated profound sensorineural hearing loss ascribable to the lesion, and facial nerve sequelae were noted in nearly 10% of cases. Cholesteatoma complicated almost 40% of cases, usually in the form of a canal cholesteatoma. Ten new cases of temporal bone fibrous dysplasia are described not only to further clarify the spectrum of otologic sequelae but also to help illustrate available treatment options. In addition, this report documents, in three new cases, the previously undescribed progression of conductive hearing loss to profound sensorineural deafness secondary to fibrous dysplasia.
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Bone scintigraphy is a sensitive imaging modality for detecting early lesions and polyostotic involvement in fibrous dysplasia. Common findings include multiple areas of focal uptake that are often unilateral and typically involve the ribs, tibia, femur, and craniofacial bones. A knowledge of various skeletal manifestations of fibrous dysplasia is helpful to distinguish it from Paget's disease, osteoblastic metastasis, and fractures. Several recent cases representing varying involvement of fibrous dysplasia are presented and the literature is reviewed.
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