Cortical bone remodeling in parosteal osteosarcoma mimicking medullary involvement: a case with the difficulty in pre-surgical staging.

Parosteal osteosarcoma (POS) is a low-grade well-differentiated variant of osteosarcoma that affects the metaphyseal surface of a long bone. Although Grade-1 POS sometimes involve the medullary canal, such patients are not at a greater risk of local recurrence or metastases. In this report, we describe a rare case of POS in the right distal femur with an intramedullary sclerotic lesion mimicking medullary involvement caused by secondary remodeling of the underlying cortex of the tumor. A 34-year-old woman complained of having a painful hard mass in her right knee for six months. Imaging studies revealed a broad-based sclerotic mass attached to the cortex of the distal and lateral aspect of the femur, along with an intramedullary lesion. Histopathological examination of a biopsy specimen revealed Grade-1 POS. We diagnosed a medullary involvement and we performed a wide resection, including the intramedullary lesion. Histopathological examination of the resected specimen revealed that the intramedullary lesion only exhibited remodeling of the underlying tumor cortex without tumor cell invasion. To the best of our knowledge, this is the first report of such imaging features and pathological findings in a patient with POS. Our experience with the present patient indicates that good local control and overall prognosis of patients with medullary involvement in Grade-1 POS may be due to the remodeling of the underlying cortex mimicking "medullary involvement." This feature will add to the range of diagnostic difficulty experienced during the preoperative staging of POS.

A p53 gene mutation in malignant fibrous histiocytoma associated with bone infarction.

Transformed sarcomas rarely arise from bone infarct lesions, although the majority of bone sarcomas are primary in origin. However, the pathogenesis of the condition is unknown. In this report, we describe a malignant fibrous histiocytoma with a p53 gene mutation. A 59-year-old woman complained of having pain in her left knee for three months. Plain radiographs of the distal metaphysis of her left femur revealed an ill-defined lytic lesion, which was consistent with a malignant tumor in the infarct lesion. An open biopsy specimen did not show any evidence of malignancy. Immunohistochemical examination of the biopsy specimen failed to show p53 protein-positive cells. However, a mutation in the p53 gene was detected when polymerase chain reaction/single-strand conformation polymorphism (PCR-SSCP) analysis was performed. A functionally relevant p53 missense mutation in codon 273 of exon 8 [CGT (Arg) -> CAT (His)] was confirmed by direct sequencing. We concluded that this lesion was a malignant bone tumor arising from the bone infarct lesion, and we thus performed a wide resection. The histopathological diagnosis of the resected specimen was that it was a malignant fibrous histiocytoma associated with bone infarction. Immunohistochemistry revealed that the tumor cells were positive for the p53 protein. To our knowledge, our patient is the first patient having a bone infarct-associated sarcoma with a p53 gene mutation. Identification of the p53 mutation helps in diagnosing the malignant transformation of the bone infarct lesion. One pathogenesis of this condition may be a mutation in the p53 gene.

Gender-related changes in three-dimensional microstructure of trabecular bone at the human proximal tibia with aging.

Despite increasing interest in age- and gender-related bone alterations, data on trabecular microstructure at the proximal tibia are scarce. The aim of this study was to identify trabecular microstructural change at the human proximal tibia with age and gender, using micro-computed tomography (micro-CT) and scanning electron microscopy (SEM). Fifty-six proximal tibias from 28 Japanese men and women (57-98 years of age) were used in this study. The subjects were chosen to give an even age and gender distribution. Both women and men were divided into three age groups, middle (57-68 years), old (72-82 years) and elderly (87-98 years) groups. The trabecular bone specimens from the medial compartment of the proximal tibial metaphysis were examined. Trabecular bone mineral density (BMD), bone volume fraction (BV/TV) and trabecular thickness (Tb.Th) decreased between the middle-aged and elderly groups similarly in women and men. However, trabecular number (Tb.N) decreased by 13% between the middle-aged and elderly groups in women and nearly double that in men. As compared with women, men had higher BV/TV and lower trabecular separation (Tb.Sp) in the old age and elderly groups, and higher Tb.N and connectivity density (Conn.D) in the elderly group. Increased trabecular resorbing surfaces, perforated or disconnected trabeculae and microcallus formations were observed with age. These findings indicate that both BMD and BV/TV decreased at the proximal tibia with age similarly for women and men, but significant differences between women and men were observed for some microstructural parameters. These findings illustrate potential mechanisms underlying osteoporotic proximal tibial fracture.

Three-dimensional microstructure of the bone in a hamster model of senile osteoporosis.

Age-related bone loss, which is poorly characterized, is a major underlying cause of osteoporotic fractures in the elderly. In order to identify the morphological feature of age-related bone loss, we investigated sex and site (tibia, femur and vertebra) dependence of bone microstructure in aging hamsters from 3 to 24 months of age using micro-CT. In the proximal tibia and distal femur, trabecular bone volume (BV/TV), trabecular number (Tb.N), trabecular thickness (Tb.Th) and bone mineral density (BMD) increased to a maximum at 6 or 12 months and then declined progressively from 12 to 24 months of age. Trabecular separation (Tb.Sp), trabecular bone pattern factor (TBPf) and structure model index (SMI) increased with age. As compared with male hamsters, BV/TV and Tb.N were significantly lower in females at 18 and 24 months of age. Age-related decrease of trabecular BV/TV in the vertebral body was less than that of the femoral and tibial metaphyses. In the mid-femoral diaphysis, cortical bone area remained constant from 3 to 24 months of age. Cortical thickness decreased from 12 to 24 months and cortical BMD declined significantly from 18 to 24 months of age. These findings indicate that skeletal site and sex differences exist in hamster bone structure. Age-related bone changes in hamsters resemble those in humans. We conclude that hamster may be a useful model to study at least some aspects of bone loss during human aging.

Effect of combined humanPTH(1-34) and calcitonin treatment in ovariectomized rats.

We examined the combined effects of human parathyroid hormone 1-34 (hPTH) and elcatonin (ECT: a synthetic derivative of eel calcitonin) to prevent loss of bone mass, architecture and strength in ovariectomized (OVX) rats. Fifty-four female rats (aged 13 weeks) were assigned to one of nine groups: Sham (fake surgery performed), OVX, ECT (15 U/kg administered), PTH5, PTH10 and PTH20 (5, 10 or 20 microg/kg administered), and E+PTH5, E+PTH10 and E+PTH20 (15 U/kg of ECT and 5, 10 or 20 microg/kg of hPTH administered). The drug or vehicle was subcutaneously administered three times a week for 12 weeks. The femurs were removed at the completion of the experiment. The right distal femoral metaphysis was used for measuring bone mineral density (BMD), analyzing trabecular bone structure by micro-computed tomography (microCT), and conducting the bone strength test, and the left femur was used for histomorphometric analysis. Trabecular bone volume (BV/TV) and other bone mass parameters were greater in the ECT and PTH groups than in the OVX group. The number of nodes (N.Nd/TV) and trabecular number (Tb.N) were significantly greater in the ECT group, and trabecular thickness (Tb.Th) and trabecular bone pattern factor (TBPf) were significantly greater in the PTH group. These results indicate that these drugs preserve the bone architecture by different means. Analysis by means of microCT revealed that BV/TV, Tb.N, fractal D and N.Nd/TV were significantly greater in the E+PTH groups than in the PTH groups at each concentration. Trabecular separation (Tb.Sp) was significantly lower in the E+PTH5 and E+PTH10 groups than in the respective PTH5 and PTH10 groups. When the maximum load was applied in a compression test on the distal femur, the E+PTH groups had higher values than the PTH groups, however, the three point bending strength of the diaphysis of femur in the E+PTH10 and E+PTH20 groups tended to be low compared to those in the PTH10 and PTH20 groups. These results indicate that combination therapy using PTH and ECT preserves the trabecular microarchitecture better than single-drug therapy using ECT or PTH in OVX rats, however, it is necessary to optimize the calcitonin (CT) dosage and administration in order to achieve the optimal combined effect of PTH and CT.

Concurrent periosteal chondroma and enchondroma of the fibula mimicking chondrosarcoma.

We present a rare concurrence of enchondroma and periosteal chondroma in the right distal fibula that mimicked chondrosarcoma in a 13-year-old boy. Radiographs and CT scans showed a periosteal lesion producing saucerization without periosteal reaction and calcification in the distal metaphysis of the right fibula. MRI showed an intramedullary lesion adjacent to the periosteal lesion, although it was invisible at CT. There was no cortical breach on imaging and gross examination. Because both lesions represented benign cartilaginous tumors on histology, concurrent periosteal chondroma and enchondroma of the fibula was diagnosed. This combination in the same bone in a patient without enchondromatosis is exceedingly rare. Such imaging features may be confused with those of chondrosarcoma.