Evaluation and histological maturation characteristics of fibrous dysplasia and ossifying fibroma: A case series

Abstract

Background: Fibrous dysplasia (FD) and ossifying fibroma (OF) are benign fibro-osseous lesions (FOLS) that are generally considered to be separate entities distinguishable by histologic and radiographic features. The histological maturation of these lesions involves an initial fibrous state, an intermediate mixed and a final mineralised stage. Objective: To correlate the mineralisation of OF and FD with the duration of the lesion. Design: A retrospective histopathological analysis of archival material including sixteen cases documented over a three-year period was performed to distinguish FD from OF. Setting: The relevant data of FOLs diagnosed as OF and FD were retrieved from the archival records of the Departments of Oral Surgery/Oral Pathology and Histopathology/ Morbid Anatomy, Muhimbili University of Health and Allied Sciences. Results: Remarkably, in this series, none of the FD and OF lesions occurred in patients aged below 10 or over 50 years. The histopathological comparison of the various nonmineralised components in both the lesions in relation to lesion age-maturity was not statistically significant (P>0.05). Conclusion: The histopathological ratio of the mineralised to non-mineralised components may not be directly indicative of the maturity of both OF and FD. third decade of life which is different from what other studies (7,11-13,16) have reported. The difference might be attributed to variations in methodology and the number of cases evaluated in these studies. Shimazu et al. (1) reported that the crystallinity of apatite crystals in pathogenic FOL tissue exhibits an improvement with tissue maturation, approaching the level of crystallinity of the age-matched bone crystals. Zimmerman et al. (14) reported that serial roentgenograms in several cases of FD showed that some lesions became mineralised as the patient aged. The osseous or more mineralised tumours were found in older patients and the average duration of these lesions was greater. The present study suggests that the stage of mineralisation of these lesions (FD and OF) may not be directly related to the age of the lesion in terms of mineralisation to the histological components (mineralised and non-mineralised) found within them. Reed (15) studied serial biopsies in three cases of FD which showed persistence of woven bone after intervals of up to 10 years. It was believed that FD represented a permanent maturation arrest in the woven bone stage. MacDonald-Jankowski (16) reported that the variation in the density within radiographs of FD may indicate that different areas of the lesion mature at different times. However, Cooke (17) in another study did not observe radiographic changes in comparable films of FOLs over an interval of 10 years.The present study and previous other investigations reflect the complexity of these lesions in terms of histologic and radiographic maturation. Since the age of these lesions as reported in the present study may not directly affect mineralisation of histological components within them, it seems that, there could be certain regulatory mechanisms of mineralisation that are yet to be understood. The persistence of woven bone after intervals of 10 years as reported by Reed supports the assumption that once metaplastic change has taken place in these lesions to certain histological components, they could in fact persist for the whole period of the existence of the lesions. The metaplastic change seems to be controlled by cells which were oncogenic or developmental in nature but still express osteogenic phenotypes. Similarly as in the present study the mineralisation components within the analysed lesions may have been “biologically controlled” by cells and did not depend on the duration (age) or maturation of the conditions. In conclusion, the histopathological ratio of the mineralised to non-mineralised components may not be directly indicative of the maturity of both OF and FD.