A light and electron microscopic study of the adenomatoid odontogenic tumor

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.

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.

Immunohistochemical demonstration of enamel proteins in odontogenic tumors

Immunohistochemical localization of two enamel proteins, amelogenin and enamelin, in comparison with that of keratin, was determined in odontogenic tumors and the allied lesions in order to verify functional differentiation of the tumor cells as ameloblasts. Amelogenin and enamelin were demonstrated in small mineralized foci and in the tumor cells surrounding them in adenomatoid odontogenic tumor (AOT), calcifying epithelial odontogenic tumor (CEOT), and calcifying odontogenic cyst (COC). Hyaline droplets in AOT showed positive staining for both enamel proteins. These mineralized and hyaline materials were not positive for keratin, although tumor cells were positive. On the other hand, no immunoreaction for enamel proteins was obtained in ameloblastoima and odontogenic epithelial cell nests within myxoma and epulis. The results suggest that tumor cells of AOT and CEOT and lining epithelial cells of COC show ameloblastic differentiation in part, but that ameloblastoma cells do not attain functional matauration as secretory phase ameloblasts.

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.

The combined epithelial odontogenic tumour in Malaysians

The combined epithelial odontogenic tumour represents a hybrid lesion comprising primarily areas of adenomatoid odontogenic tumour intermixed with foci of calcifying epithelial odontogenic tumour. Five such cases retrieved from the files of the Division of Stomatology, Institute for Medical Research, Kuala Lumpur, and four others from the existing literature were analysed. A mean age of 18.8 years, a female preponderance (66.7%) with a male to female ratio of 1:2 and predilection for the mandible (55.6%) were observed. All cases were treated by conservative surgery and the lack of recurrence confirmed the innocuous nature of this lesion.

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.

Vascular degeneration in adenomatoid odontogenic tumour: an ultrastructural study

The blood vessels in 3 cases of adenomatoid odontogenic tumour (AOT) were investigated ultrastructurally. An estimated 70-90% of the blood vessels found in the stroma showed degenerative changes which affected both the endothelial lining and the perivascular connective tissue. These vessels showed multiplication of basal lamina and were also encircled by concentric lamellae consisting either of collagen or fine filaments measuring 5-15 nm in diameter. Degradation of the layered collagen into fine filaments similar to those forming the concentric layers was observed. The present results suggest that the fine filaments of the concentric lamellae probably result from degradation of the layered collagen surrounding these vessels.

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.

Adenomatoid odontogenic tumor mimicking a globulo-maxillary cyst

A case of an adenomatoid odontogenic tumor (AOT) simulating a globulo-maxillary cyst is described. Clinical, radiographic and microscopic findings as well as the differential diagnosis are discussed. The present case brings the number of AOT cases without any relationship to an impacted tooth to 23; the number of cases resembling a globulo-maxillary cyst to 6.

Adenomatoid odontogenic tumor: clinicopathologic and ultrastructural concepts

Two cases of adenomatoid odontogenic tumor have been presented, along with a review of the literature. One tumor had a rather typical presentation, occurring in a 12-year-old in association with an impacted canine tooth. Subsequent electron microscopic evaluation of this case provided corroboration of other recently published findings. In this case there was a striking accumulation of what could have been secretory granules at the pole of the cell nearest a "duct-like" space. This cell had ultrastructural characteristics in common with a preameloblast. The second case occurred in a more unusual situation, the patient being a 32-year-old man, with the AOT developing in the mandible between the roots of the canine and first premolar. Both patients were treated successfully by simple enucleation of the lesion.

The distribution and morphologic variation of hyaline deposits in odontogenic lesions

The deposits of homogeneous hyaline substances present in epithelium-containing odontogenic lesions were evaluated in 201 tumors. The material was evaluated to establish the types of odontogenic lesions capable of producing the substance, its frequency of occurrence, its microscopic variation, and the different morphologic relationships of the substance to the odontogenic epithelium present in the lesions. The deposits were found in 40.3 percent of the 201 odontogenic tumors and frequently in several other nonneoplastic odontogenic lesions. It was most consistent in odontomas but was found to some extent in all types of epithelium-containing odontogenic tumors. It was present either in a basement membrane location or as a diffuse deposit in the connective tissue. In the latter location, the deposits commonly contained enclaved islands of odontogenic epithelium and had a distinct tendency to calcify. The study also suggests that since some odontogenic tumors may contain large amounts of the hyaline deposits, multiple sections through different parts of the tumor may be required to find the epithelial elements necessary for the correct diagnosis.

The eosinophilic and amyloid-like materials in adenomatoid odontogenic tumor

This paper is concerned with the relationship between eosinophilic material (EM) and amyloid-like material and adenomatoid odontogenic tumors. In duct-like structures between opposing rows of tall columnar cells, EM did not stain for amyloid. Under electron microscopy, EM was composed of fibrillar and granular materials, and the fibrillar material was not amyloid. Two different kinds of EM were found in solid cell masses. Lesions from cases 2, 3, 4 and part of case 1 contained small droplet-shaped EM and these EM did not stain for amyloid. Case 1 also contained EM that stained positively for amyloid. The structure of amyloid positive EM resembled developing enamel of human tooth germs. This material was tubular and finely granular. The tubular material resembled enamel matrix fibers rather then amyloid and the fine granular material was stippled. The cells surrounding EM appeared similar to ameloblasts between secretory and maturation stages.

Adenomatoid odontogenic tumor: light and electron microscopic study

A case of adenomatoid odontogenic tumor involving the right upper cuspid region of a 17-year-old girl is described. In light microscopy, liminal structures and rosette-like structures were found in the parenchyma of the tumor. Electron microscopic observations revealed that the rosette-like structures were less organized than the luminal structures; the luminal structures are supposed to be associated with secretory activities including the formation of calcified material which show the apatite pattern by electron diffraction. The origin and differentiation of cells constituting the tumor are discussed.

The ultrastructure of the adenomatoid odontogenic tumor

An adenomatoid odontogenic tumor (AOT) which occurred in the maxilla of an 8-year-old boy was studied by the light and electron microscopy. The tumor was found to contain cells resembling preameloblasts, the stratum intermedium, and the stellate reticulum, suggesting its origin from the enamel organ, in agreement with previous reports. Characteristic ductlike structures are thought to be formed as a result of secretory activity of the tumor cells, rather than degeneration. Duct-lining cells ultrastructurally similar to preameloblasts were found to contain electron-dense granules. These granules are believed to play a role in secretion by tumor cells, a concept not previously considered. The results of previous ultrastructural studies of the AOT are reviewed and summarized.

Epithelio-mesenchymal morphology in ameloblastic fibro-odontoma: a light and electron microscopic study

Five cases of ameloblastic fibro-odontoma were examined by light and electron microscopy. The ultrastructure of the epithelio-mesenchymal interface was compared with the morphology of the normally developing tooth germ. It was noted that the ultrastructure of the tumors was identical with the normally developing odontogenic tissues up to but not including the differentiation of mesenchymal cells into tall columnar odontoblasts. The absence of odontoblasts in the ameloblastic fibro-odontomas results in an absence of tubular dentin in place of which a homogeneous collagen-containing material is synthesized. The failure of mesenchymal cells to acquire the morphology of tall columnar odontoblasts probably is due to the absence of the normally occurring induction of the mesenchyme by the odontogenic epithelium.

Adenomatoid odontogenic tumor: ultrastructural demonstration of two cell types and amyloid

A typical adenomatoid odontogenic tumor removed from a 13-year-old female was studied by light and electron microscopy. The tumor was composed of two types of epithelial cells: Type I cells were cuboidal and occurred in nests or formed ductlike structures and Type II cells were smaller and spindle shaped. The formation of extracellular masses of amyloid was found in association with Type I epithelial cells, and amyloid formation was not observed in association with Type II cells. Results suggest that the lesion is of enamel organ origin, derived from cells of the inner enamel epithelium at the pre-ameloblastic stage, stellate reticulum and stratum intermedium. The origin of this amyloid material is unknown; however, it may be of enamel protein origin which, like amyloid, may have a beta-protein conformation.

Ultrastructural study of adenomatoid odontogenic tumor

Two cases of adenomatoid odontogenic tumor were examined by light and electron microscopy. Morphologically the tumors could be divided into four layers. The ultrastructure of the tumor cells of each layer was revealed to be similar respectively to that of four layers seen in the enamel organ of a normal tooth germ. Duct-like structures and eosinophilic small areas were frequently present in compactly proliferating cell layers. Short columnar cells forming duct-like structures and eosinophilic small areas appeared similar ultrastructurally to ameloblasts during predentin formation. Therefore it seems reasonable to assume that this tumor originates from the enamel organ. The contents in the lumen of each eosinophilic small area varied, and seemed to be secreted into the stroma by circumscribing epithelial tumor cells. A fine filamentous layer was present in both of the duct-like structures and some of the eosinophilic small areas, and the former was different from the latter with respect to the alcian blue (pH 2.5) and toluidine blue (pH 4.4) staining reactions.

An ultrastructural study of the calcifications in calcifying odontogenic cysts and odontomas

The calcifications associated with the epithelium of the calcifying odontogenic cyst and odontoma were studied ultrastructurally and found to be of three types: (1) spherical calcifications which form on ghost cells and which therefore are dystrophic, (2) spherical calcifications which appear to be dysplastic enamel, and (3) irregularly shaped, diffuse calcifications which form on a collagenous matrix and appear to by dysplastic dentin or cementum.