[Ultrastructural study of a case of monostotic fibrous dysplasia].

Ultrastructural study of a case of fibrous dysplasia taken together with the rare data in the literature confirmed that the morphological characteristics of this lesion consist of a typical appearance of "woven bone", irregularly mineralised, containing osteocytes and bordered by osteoblasts, clearly distinct from fibroblasts. The cell elements are invariably endowed with a large microbrillary cytoplasmic brush, apparently made up of scleroproteins and showing the usual ultrastructural characteristics associated with low metabolic activity. The presence of myofibroblasts is unlikely. The numerous mastocytes seen by light microscopy show a large number of "rosette" granulation at electrom microscopy, which distinguishes them from the mastocytes seen in osseous modelling. These morphological data provide no decisive argument in favour of the truly dysplasic nature of this lesion.