[An electron microscopic study on osteoblastoma--ultrastructure and fine localization of alkaline phosphatase].

Three cases of osteoblastoma were studied by electron microscopy. They included two cases of conventional osteoblastoma and one case of aggressive osteoblastoma. In conventional osteoblastoma, ultrastructural features and location of alkaline phosphatase activity of the osteoblast-like cell were similar to those of normal osteoblast. On the other hand, aggressive osteoblastoma cell (case 3) showed different structure from those of a normal osteoblast; the nucleus of the tumor cell showed irregular surface with a small degree of heterochromatin, and poorly developed cytoplasmic organellae. Cytochemically, alkaline phosphatase activity was noted not only on the cytoplasmic membrane, but on the abundant vesicles in the cytoplasm. From these findings we conclude that the aggressive osteoblastoma cells are more immature in morphology and show increased synthesis of alkaline phosphatase.

Studies on the fine structure of osteoblastoma with notes on the localization of nonspecific acid and alkaline phosphatase.

Electron microscopy of two osteoblastomas revealed the existence of three distinct types of cells in this tumor: osteoblast like, macrophage like, and multinucleated giant cells. In addition to the lysosomes, most Golgi cisternae and vesicles in the osteoblast like cells showed evidence of acid phosphatase activity. Deposits of lead phosphate indicating the site of this enzyme in the macrophage like cells were confined to the large and abundant lysosomes. Wide spread deposition of final product was noted in the cytoplasm of the multinucleated giant cells, both in conventional lysosomes, Golgi regions and special organelles probably corresponding to GERL. With regard to nonspecific alkaline phosphatase, final product indicating the location of enzyme activity was confined to the plasma membranes and associated vesicular and vacuolar structures in the osteoblast like cells. The findings suggest that the giant cells in osteoblastomas participate in lytic bone destructive and resorptive processes while osteoblast like cells appear to be osteoid and bone forming carriers of the neoplastic properties of the tumor.

Mechanism of intramedullary high intensity area on T2-weighted magnetic resonance imaging in osteoid osteoma: a possible role of COX-2 expression.

To study the mechanism and pathophysiology of the development of intramedullary high intensity areas on T2-weighted magnetic resonance images (MRI) in cases of osteoid osteoma, we examined the expression of cyclooxygenase-2 (COX-2) in the nidus and surrounding bone tissues. In all six cases showing a marked intramedullary high intensity area adjacent to the nidus before surgery, neoplastic osteoblasts inside the nidus showed strong and diffuse COX-2 immunoreactivity. On the other hand, the osteoblasts rimming the surrounding reactive bone were COX-2 negative. In two cases examined by reverse transcription-polymerase chain reaction (RT-PCR), COX-2 mRNA was detected in abundance in the nidus. Histologically, vascular dilatation together with intramedullary edema was observed in all cases, which was probably reflected as a high intensity area on T2-weighted MRI. From our study, a high level of COX-2 expression in neoplastic osteoblasts in the nidus of osteoid osteomas may cause the secondary changes depicted by MRI.

Intraarticular osteoid osteoma associated with synovitis: a possible role of cyclooxygenase-2 expression by osteoblasts in the nidus.

To clarify the condition of development of synovitis associated with intraarticular osteoid osteoma (OO), expressions of cyclooxygenase-2 (COX-2) protein and its messenger ribonucleic acid were investigated both in the nidus and the synovial tissue using immunohistochemical and reverse transcription-polymerase chain reaction analyses. Diffuse and strong COX-2 immunoreactivity was found in osteoblast-like tumor cells in the nidus of all six cases of OO (three of six cases were intraarticular OO associated with synovitis) and one case of osteoblastoma associated with synovitis. Expression of COX-2 messenger ribonucleic acid was demonstrated in one case of OO associated with synovitis, and was higher in the nidus than that in the inflamed synovial tissue. However, there were no significant difference between the nidus and synovium in the expression of cytosolic phospholipase A2, one of the enzymes involved in arachidonic acid metabolism, and inflammatory cytokines such as interleukin-1beta and tumor necrosis factor alpha. Finally, as there was only one case in which the examinations of gene expression were performed, no definitive overall conclusions could be reached; rather it is suggested that COX-2 expressed primarily by osteoblasts in the nidus of intraarticular OO may play a role in activating the pathway of arachidonic acid metabolism, resulting in synovitis of the involved joint.