Adenomatoid odontogenic tumor: light and electron microscopic study

A case report and short review on changing trends in the site of occurrence of adenomatoid odontogenic tumor: Unravelling the past 15 years

Adenomatoid odontogenic tumor (AOT) is an uncommon benign odontogenic lesion, with debatable histogenesis and variable histopathology. A systematic and diverse insight into the evolution, clinical presentation, histology, and immunohistochemical findings of this lesion is reviewed and presented. We reviewed the data published from 2000 to 2014 of approximately 255 cases that revealed a significant change in the incidence of predominant site involved, in contrast to the findings published by Reichart. We have also included the chronological order of events leading to the coining of the term AOT, which shows the curiosity that has been dedicated to understanding the lesion. Immunohistochemistry is considered to be a hallmark in pathology for learning the molecular pathogenesis and giving a correct final diagnosis. Several markers have been used to investigate and understand this lesion, and a compilation of the findings has been tabulated.

Cytokeratin 14 and cytokeratin 18 expressions in reduced enamel epithelium and dentigerous cyst: Possible role in oncofetal transformation and histogenesis- of follicular type of adenomatoid odontogenic tumor

Introduction:

Odontogenic cysts and tumors arise from the structures and remnants associated with tooth development. Cysts and tumors derived from the odontogenic tissues constitute an unusually diverse group of lesions. This diversity reflects the complex development of the dental structures, since all these lesions originate through some alteration from the normal pattern of odontogenesis. Cytokeratin (CK) 14 is the typical intermediary filament of odontogenic epithelium, CK 18 is the major components of the intermediate filaments of simple or single layered epithelial tissue; it is not expressed in stratified squamous epithelium. The present study was undertaken to understand the expression pattern of these cytokeratins in dentigerous cyst, dental follicular tissue, adenomatoid odontogenic tumor (AOT) and unicystic ameloblastoma.

Materials and Methods:

The present study consists of 60 specimens consisting of 20 samples of Dentigerous cyst, 20 samples of Reduced enamel epithelium/dental follicles, 10 samples of Follicular type of AOT, 10 samples of unicystic ameloblastoma. The sections of these specimens were stained for CK 14 and CK 18. The number of cells positive for CK 14 and CK 18 was counted per 100 cells. The cells were counted in four randomly selected high-power fields and the mean was calculated. Scoring of cytokeratin 14 expressions was done using Remmele score.

Results:

The highest expression of cytokeratin 14 was noted in AOT, least was seen in dental follicle/Reduced enamel epithelium (REE). CK18 was negative in all the cases included in the present study.

Conclusion:

In the present study, the expression of CK14 was noted in AOT, Dentigerous cyst (DC), Unicystic Ameloblastoma (UCA) and Dental follicle/REE. The expressions between these lesions were compared. These expression pattern may provide an insight to the histogenesis of AOT.

Adenomatoid odontogenic tumor: retrospective study of 15 cases with emphasis on histopathologic features

Adenomatoid odontogenic tumor (AOT) is an uncommon benign epithelial lesion of odontogenic origin and, thus far, only few studies regarding the frequency of its many histopathologic features have been published in the literature. Thus, the aim of this study was to perform a retrospective analysis in a case series of AOT, with emphasis on the histopathological features. Fifteen cases of AOT were studied considering their clinical, radiographic and histopathologic aspects. Twelve cases affected females and the mean age was 16.2 years. The anterior maxilla was the most common site (66.6 %) and radiographically most cases showed a unilocular radiolucency with well-defined borders (57.1 %). Histologically, most cases exhibited predominantly a solid growth pattern (46.7 %) or a similar proportion of solid and cribriform patterns (46.7 %). Eosinophilic amorphous material ("tumor droplets") was found in all cases (100 %). Most tumors showed duct-like spaces (93.3 %) and convoluted structures (60.0 %) whereas a minor proportion of cases presented calcifying epithelial odontogenic tumor (CEOT)-like areas (26.7 %). Variable amounts of calcified material were found in most AOTs (80.0 %) whereas osteodentin and perivascular hyalinization were seen only rarely (6.7 % each one). Five (33.3 %) cases had areas mimicking a dentigerous cyst and most of these were diagnosed in females (80.0 %). Regarding the histopathologic features, our results suggest that AOTs usually show predominance of solid pattern or a similar proportion of solid and cribriform patterns while osteodentin and perivascular hyalinization are rarely seen in these tumors. In addition, areas mimicking a dentigerous cyst and CEOT-like areas are relatively infrequent findings in AOTs.

Critical evaluation of the radiological and clinical features of adenomatoid odontogenic tumour

OBJECTIVES

The aim of this study was to evaluate the radiological and clinical features of adenomatoid odontogenic tumours (AOTs).

METHODS

A total of 272 cases (267 from the English-language literature and 5 new cases) were analysed with special emphasis on their radiological features.

RESULTS

The patients' ages at time of diagnosis ranged from 3 years to 82 years (mean 18.4 years). The maxilla-to-mandible ratio was 1.7:1. Mandibular lesions were significantly more frequent among patients older than 16 years (p = 0.032). Expansion of the cortex was significantly more prominent among patients older than 16 years (p = 0.045). There was a positive correlation between the size of the lesion and the age of the patient at the time of diagnosis (p = 0.016). The size was also associated with increased root resorption (p < 0.001), ill-defined borders (p < 0.001), expansion (p < 0.001) and perforation of the cortex (p < 0.001). Small opacities were present in 77% of lesions and were associated with expansion of the cortex (p = 0.043). The significant radiological features in patients aged 30 years and above were root resorption (p = 0.013) and lesions crossing the midline (p = 0.019).

CONCLUSIONS

The size of an AOT is influenced by the patient's age. It is also associated with root resorption, ill-defined borders, expansion and perforation of the cortex, but it cannot be ruled out that those changes reflect a longer duration of the lesion.

Study on the origin and nature of the adenomatoid odontogenic tumor by immunohistochemistry

The adenomatoid odontogenic tumor (AOT) is a clinically benign lesion. Discussions about the AOT hamartomatous or neoplastic nature, and the probable odontogenic epithelial cell it originates from still exist. This research aimed to study and discuss the subject by the immunohistochemical detection of cytokeratins, laminin, collagen IV, PCNA and p53 in 8 tumor samples and 8 dental follicle samples containing reduced enamel epithelium. The results have shown that CK14 labelling indicated differentiation grades for secreting ameloblasts or ameloblasts in the post-secreting stage in the adenomatoid structure of AOT. Laminin, found on the luminal surface of adenomatoid structures, was compatible with the reduced enamel epithelium during the "protective stage of amelogenesis". PCNA specifically labelled the spindled areas and peripheral cords of the AOT, indicating that these areas are responsible for tumor growth. After considerations about pathogenesis, the authors suggested that the nature of AOT is hamartomatous with histogenesis from the reduced enamel epithelium.

ADENOMATOID ODONTOGENIC TUMOR ARISING FROM THE MANDIBULAR MOLAR REGION: A CASE REPORT AND REVIEW OF THE LITERATURE

This case report describes a rare case of an adenomatoid odontogenic tumor (AOT) arising in the mandibular third molar region of a 20-year-old female. The tumor was a well-circumscribed intraosseous lesion with an embedded tooth. Histologically, the induction of extensive globular calcification was evident in addition to the characteristic histological features of AOT. The present case lends support to the categorization of AOT as an odontogenic tumor consisting of a disorderly mixture of odontogenic epithelium and odontogenic ectomesenchyme with calcification.

Cytokeratins in epithelia of odontogenic neoplasms

Neoplasms and tumours related to the odontogenic apparatus may be composed only of epithelial tissue or epithelial tissue associated with odontogenic ectomesenchyme. The immunohistochemical detection of different cytokeratins (CKs) polypeptides and vimentin has made it easier to explain the histogenesis of many epithelial diseases. The present study aimed to describe the immunohistochemical expression of cytokeratins 7, 8, 10, 13, 14, 18, 19 and vimentin in the epithelial components of the dental germ and of five types of odontogenic tumours. The results were compared and histogenesis discussed. All cells of the dental germ were positive for CK14, except for the preameloblasts and secreting ameloblasts, in which CK14 was gradually replaced by CK19. CK7 was especially expressed in the cells of the Hertwig root sheath and the stellate reticulum. The dental lamina was the only structure to express CK13. The reduced epithelium of the enamel organ contained CK14 and occasionally CK13. Cells similar to the stellate reticulum, present in the ameloblastoma and in the ameloblastic fibroma, were positive for CK13, which indicates a nature other than that of the stellate reticulum of the normal dental germ. The expression of CK14 and the ultrastructural aspects of the adenomatoid odontogenic tumour probably indicated its origin in the reduced dental epithelium. Calcifying odontogenic epithelial tumour is thought to be composed of primordial cells due to the expression of vimentin. Odontomas exhibited an immunohistochemical profile similar to that of the dental germ. In conclusion, the typical IF of odontogenic epithelium was CK14, while CK8, 10 and 18 were absent. Cytokeratins 13 and 19 labelled squamous differentiation or epithelial cells near the surface epithelium, and CK7 had variable expression.

The adenomatoid odontogenic tumour: ultrastructure of tumour cells and non-calcified amorphous masses

The ultrastructure of tumour cells and tumour droplets (TD, non-calcified amorphous masses) was studied in three cases of AOT using freshly prepared tissue. The fine structure of the epithelial tumour cells (cell type I-III) corresponded to that of earlier descriptions. The extracellular location of TD was clearly demonstrated. TD were of varying, sometimes bizarre, configuration. Some TD showed a homogeneous matrix; however, in addition most revealed electron-dense plaques. At high magnification, homogeneous types of TD showed only tubular elements; all others revealed granulo-tubular structures. The tubular elements were arranged concentrically. The nature of the TD is discussed and compared to former interpretations. From the present ultrastructural findings, it appears that the TD most probably represent some form of enamel matrix and as such may be considered a type of pre-enamel. Further studies are needed to elucidate the complex structure of the TD-material so characteristic of the AOT.

The nature of the eosinophilic and laminated masses in the adenomatoid odontogenic tumor: a histochemical and ultrastructural study

The eosinophilic and laminated masses in AOT were investigated with the light and electron microscope in two cases. The results showed that the eosinophilic amorphous masses were heterogenous and consisted mainly of three types of fibrils. These were: thin collagen, electron dense fibrils probably resulting from degradation of collagen and masses of amyloid filaments with or without collagen fibers in normal and degraded forms. In addition some of the eosinophilic deposits resulted from changes surrounding blood vessels which led to deposition of either collagen or fine filaments arranged into layers around these vessels. In all these areas there was a peripheral layer of fine filaments perpendicular to the epithelial basal lamina, similar to that found in early dentin formation. This layer may be responsible for the reticulin staining found in this tumor. On the other hand the great majority of the laminated masses represented calcified amyloid with or without areas of calcified degraded collagen which were indistinguishable from amyloid. The results suggest that the various fibrils forming the eosinophilic masses in AOT are probably related and may be the result of changes in blood vessels. They also revealed that calcification involves mainly amyloid.

Adenomatoid odontogenic tumor: biologic profile based on 499 cases

Topographically, the AOT occurs in peripheral and central variants, the latter further in follicular (with embedded tooth) and extrafollicular (no embedded tooth) types. The AOT is slow growing with few or no symptoms. Tumor growth may cause displacement of teeth rather than root resorption. The follicular AOT mimics a follicular cyst, the extrafollicular a residual or "globulo-maxillary" cyst and the peripheral a gingival fibroma. All variants of AOT show identical histologic features. The central variants account for 97.2%, 73.0% of which are follicular. The follicular variant (M:F ratio 1 to 1.9) is three times as frequent as the extrafollicular. The follicular variant is diagnosed earlier in life (mean age 17 yr) than the extrafollicular (mean age 24 yr). 53.1% of all variants occur within the teens (13-19 yr). Follicular AOT is associated with one embedded tooth in 93.2%. Maxillary permanent canines account for 41.7% and all four canines for 60.1% of AOT-associated embedded teeth. Ranking four among the odontogenic tumors the AOT is not a particularly rare tumor. Conservative surgical excision is the treatment of choice. Documented recurrences have not been reported.

A pigmented adenomatoid odontogenic tumor

Occasional reports have described the presence of melanin in various odontogenic lesions. A case of melanin pigmentation in an adenomatoid odontogenic tumor is described.

Adenomatoid odontogenic tumour: co-expression of keratin and vimentin

Immunohistochemical observations of intermediate sized proteins in five cases of adenomatoid odontogenic tumour (AOT) are described. The immunohistochemical detections of keratins were made with polyclonal antiserum (TK, 41-65 kDa) and three monoclonal keratin antibodies (KL1: 55-57 kDa; PKK1: 40, 45, and 52.5 kDa and nos. 19, 18, 8; K8.12: nos. 16, 13) and vimentin and desmin monoclonal antibodies. Histologically, the tumour epithelia could be divided into two types: type A cells were a spindle or columnar shape and formed solid, ductal, tubular or whorled structures. Type B cells were small and compact cells at the periphery of the A cell-containing focus. Immunohistochemically, the type A cells showed very slight reaction with all antibodies to keratins, whereas the type B cells indicated slight-to-moderate expression of keratin and vimentin, and showed coexpression. Both types of cell showed a negative reaction for desmin. Only one case was associated with cystic lesions, and the cyst-lining was composed of thin squamous epithelium. Keratin expression in this epithelium was strong. In the histogenesis of AOT it was postulated that the tumour cells may have originated from undifferentiated odontogenic epithelium or stratum intermedium cells.