Ultrastructure of giant-cell lesions. Mononuclear cells in peripheral giant-cell granulomas

Intravascular fibrin thrombi and endothelial cell damage in central giant cell granuloma

Two cases of central giant cell granuloma were studied ultrastructurally. The majority of vessels showed intravascular fibrin thrombi and endothelial cell damage, with gaps in their walls. Plasma, red cells and fibrin were seen subendothelially. The basal lamina was absent from endothelial cells where these components were in contact with their plasma membrane; otherwise it showed multiplication. It is suggested that the absence of basal lamina is the result of degeneration and that these vessels are probably venules and capillaries rather than lymphatics. Myofibroblasts were the dominant stromal cells. Giant cells had little phagocytic activity. It seems that the main function for the stromal cells is the repair of the haematoma and the damaged vessels. It is proposed that the term giant cell reparative granuloma is appropriate, but it should not be used indiscriminately for all jaw lesions containing giant cells.

Peripheral giant cell granuloma. An immunohistochemical and ultrastructural study

OBJECTIVE

To study the nature of multinucleated and mononuclear cells from peripheral giant cell granuloma (PGCG).

MATERIALS AND METHODS

Formalin-fixed, paraffin-embedded sections of 40 cases of PGCG were immunohistochemically stained for vimentin, alpha I-antichymotrypsin, CD68, S-100 protein, lysozyme, leucocyte common antigen (LCA), factor VIII-related antigen and muscle cell actin. Six cases of PGCG were also studied by transmission electron microscopy.

RESULTS

Vimentin, alpha I-antichymotrypsin and CD68 were expressed in both the mononuclear and multinucleated giant cells. Dendritic mononuclear cells, positive for S-100 protein, were noted in 67.5% of the lesions, whereas lysozyme and leucocyte common antigen were detected in occasional mononuclear cells. Ultrastructural examination showed mononuclear cells with signs of phagocytosis and sometimes interdigitations with similar cells. Others presented non-specific characteristics and the third type exhibited cytoplasmic processes and occasional Birbeck granules. Some multinucleated giant cells showed oval nuclei, abundant mitochondria and granular endoplasmic reticulum whereas others presented with irregular nuclei and a great number of cytoplasmic vacuoles.

CONCLUSIONS

Immunohistochemical and ultrastructural results suggest that PGCGs of the jaws are composed mainly of cells of the mononuclear phagocyte system and that Langerhans cells are present in two thirds of the lesions.

Myofibroblasts in peripheral giant cell granuloma. Light and electron microscopic study

Myofibroblasts are found in various pathologic conditions including lesions containing giant cells, such as central giant cell granuloma and the giant cell tumor of tendon sheath (nodular tendosynovitis). In the present study, myofibroblasts were found in peripheral giant cell granuloma (PGCG) using the TP-Levanol fast cyanine 5RN histochemical procedure and electron microscopy. A number of myofibroblasts displayed intracellular collagen fibrils. The presence of myofibroblasts supports the reactive nature of PGCG.

The multinucleate cells in giant cell granulomas of the jaw are osteoclasts

The giant cell granuloma of jaw is a well-vascularised lesion comprising a mononuclear cell infiltrate with a large number of giant cells. It has been suggested that the lesion is reparative in nature, rather than neoplastic, and that the giant cells are phagocytes accumulating in chronic reparative granulation tissue. However, the nature of the multinucleate giant cells never has been established. One possibility is that the constituent giant cells are osteoclasts. The authors assessed expression by the giant cells of several osteoclast-specific characteristics: excavation of bone; motility inhibition by calcitonin (CT); and binding of osteoclast specific monoclonal antibodies. Two tumors were disaggregated and incubated on slices of cortical bone in the presence and absence of CT. Both tumors were found to excavate bone, a function unique to osteoclasts. The giant cells also were responsive to CT, resulting in cytoplasmic quiescence and inhibition of bone resorption. Two osteoclast-specific monoclonal antibodies bound all the giant cells in one central and six peripheral tumors examined immunohistochemically. These results provide strong evidence for the osteoclastic nature of the giant cells. The presence of alkaline phosphatase-positive cells forming woven bone in giant cell granulomas suggests that osteoblasts are present in the lesion. As cells of osteoblastic lineage are known to regulate osteoclastic function, it may be that osteoblasts account for the characteristic infiltration of osteoclasts into giant cell granulomas of jaws, either as part of a reparative response by reactive osteoblasts or as an infiltrate induced by osteoblasts of aberrant function, as suggested for giant cell tumors of bone.

Myofibroblasts in central giant cell granuloma of the jaws: an ultrastructural study

The ultrastructure of stromal mononuclear cells and giant cells were studied in two cases of central giant cell granuloma of the jaws. The majority of stromal cells superficially resembled fibroblasts, but also contained intracytoplasmic myofilaments with electron dense bodies similar to smooth muscle cells. These cells were referred to as myofibroblasts. The other type of mononuclear cells resembled macrophages. Many of the myofibroblast type cells appeared close to giant cells and signs of early fusion between them could be demonstrated. It is suggested from these results that the giant cells in central giant cell granuloma form and increase in size through fusion of these cells.

Hyperplastic lesions of the gingiva and alveolar mucosa. A study of 175 cases

175 'epulides' were studied clinically and histologically. The lesions were histologically reclassified into three groups: granulomatous, fibromatous and giant cell lesions. The granulomatous group was four times and the giant cell group 1.5 times more frequent in females. It is suggested that the expression epulis should be abandoned as a microscopic designation for lesions in the oral mucosa, as it is only a non-specific topographico-clinical concept comprising histogenetically and histomorphologically differing lesions and therefore does not represent a uniform group. The suggested new terms for the three types of hyperplastic lesions are oral mucosal granulomatous hyperplasias (including such diagnostic terms as granulomatous gingivitis, gingivitis of pregnancy, granuloma gravidarium, pyogenic granuloma, epulis angiomatosa and epulis telangiectaticum), oral mucosal fibrous hyperplasias (including such diagnostic terms as fibrous epulis, epulis fissuratum, fibroepithelial lesions, denture injury tumor and peripheral odontogenic fibroma) and oral mucosal giant cell hyperplasia (including such diagnostic terms as peripheral giant cell granuloma and giant cell epulis).

Electron microscopic study of peripheral giant-cell reparative granuloma

Six giant-cell tumors have been examined by electron microscopic methods in order to determine their histogenesis and to expand knowledge of cell structures. The examination of giant cells revealed an abundance of cell organelles, especially mitochondria. Apart from typical stromal cells, such as fibroblasts, macrophages, and mast cells, clusters of stromal "light" cells were often found with an intimate relation between their cell membranes. The role and function of these cells is not well known. Between fibroblasts of regular appearance with a small number of cytoplasmic organelles, others were found with an incrased number of mitochondria. These cells often formed aggregates. This suggests that giant cells develop through the association of stroma fibroblast cells.

[Central giant cell granuloma: histochemical and ultrastructural study on its histogenesis (author's transl)]

Until now numerous studies on central giant cell granuloma of jawbones have not been able to reveal the histogenesis of this tumourlike lesion. The aim of the present investigation in two surgically proven cases was to study this question by means of histochemical and electron-microscopic methods. Rather similar histochemical properties were shown in giant cells and pericytes of capillary sproute penetrating the granuloma. Cell fusion occurred between both cell types as was observed by electron microscopy. The process of cell fusion is defined by characteristic interdigitations of cell membranes. Therefore pericytes are believed to be the stem cells of multinucleated giant cells in giant cell granuloma. The abundance of giant cells usually occurring in the granuloma might be explained by plenty of capillary sprouts made up by clusters of pericytes. The factors inducing the pericytic cell fusion process are still unknown. The question arises whether cytogenesis of giant cells in giant cell granuloma might be similar in other giant cell lesions or even in the development of multinucleated osteoclasts.