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Adenomatoid Odontogenic Tumor of the Mandible: A Case Report of an Unusual Presentation

Sumith Gunawardane, Kanchana Kapugama, M.M Hatharasinghe, Primali Jayasooriya, W M Tilakaratne

Abstract: Adenomatoid Odontogenic Tumor (AOT) is a benign odontogenic tumor which is often misdiagnosed as an odontogenic cyst. It presents as a noninvasive lesion of the jaws with a slow but progressive growth. It is predominantly seen in young females, which usually arise in the second or third decade, located frequently associated with unerupted canines in the maxilla. This report describes a rare presentation of AOT in the mandible which occurred in a middle aged male, which was not associated with an impacted tooth.

Keywords: Adenomatoid Odontogenic tumor, odontogenic tumor

Citation: Sumith Gunawardane, Kanchana Kapugama, M.M Hatharasinghe, Primali Jayasooriya, W M Tilakaratne, Adenomatoid Odontogenic Tumor of the Mandible: A Case Report of an Unusual Presentation. American Journal of Medical Case Reports, 4 (9). 324-327. January 2016. doi:10.12691/ajmcr-4-9-9

1. Introduction

Adenomatoid Odontogenic Tumor (AOT) is a relatively uncommon distinct neoplasm that was first described by Steensland in 1905. [1] From 1905 to 1969 many different names like adenoameloblastoma, ameloblastic adenomatoid tumor, adamantinoma, epithelioma adamantinum or teratomatous odontoma have been used to define the lesion currently calls as AOT. [2] Finally in 1969 Philipsen and Birn proposed the term ‘Adenomatoid Odontogenic Tumor’ and suggested that it should not be regarded as a variant of ameloblastoma because of its different behavior [3] and it was adopted by World Health Organization in 1971 [4].

Like all other odontogenic tumors, the specific stimulus that triggers proliferation of the progenitor cells of AOT is unknown. Because of its exclusive occurrence within the tooth bearing areas of jaws (most closely associated with an unerupted or impacted tooth) and its cytologic resemblance to the dental lamina and reduced enamel epithelium, there is an agreement that the AOT is of odontogenic origin [5].

AOT is an uncommon odonogenic tumor with a frequency of 2.2-7.1%. It is referred as “Two –Third tumor” because 2/3rd of tumors affect females, 2/3rd occur in the second decade and 2/3rd of tumors occur with impacted teeth. It also affects the maxilla more commonly than the mandible in a ratio of 2:1. [4] The clinical, radiological, histopathological and immunhistological features aid in the accurate diagnosis of the lesion.

Clinically AOT is a slow growing, benign, odontogenic, epithelial tumor which is commonly located in the anterior region of the maxilla. They normally, produce a slow swelling not accompanied by pain. [6] This tumor growth will cause expansion of the surrounding bone and displacement of teeth rather than root resorption. [7] However, the slow growing nature of the lesion may cause the patients to tolerate the swelling for years until it produces an obvious deformity. Although this tumor has been believed to be a hamartoma rather than a neoplasm, the lesion may rarely exhibit aggressive behaviour such as becoming unusually large or spreading into the intracranial space [8,9].

AOT occurs in intra osseous and peripheral forms. The intrabony variant comprise the follicular and extrafollicular types. The follicular type (accounting for 73% of cases), has a central lesion associated with an embedded tooth; the extrafollicular type (24% of cases) has a central lesion and no connection with the tooth; and the peripheral variety (3% of cases). [10] Two thirds of the intra bony cases have scattered radiopacities within the radiolucency. [11] It has also been found that intra oral radiographs, rather than panoramic radiographs are better suited for displaying the discrete calcific deposits [12].

According to the second edition of the World Health Organization journal ‘Histological Typing of Odontogenic Tumors’, AOT is defined as ‘a tumor of odontogenic epithelium with duct-like structures and varying degrees of inductive changes in the connective tissue. The tumor may be partly cystic, and in some cases the solid lesion may present only as masses in the wall of a large cyst. [14] Histologically, the most conspicuous feature is cuboidal or columnar epithelial cells forming nests or rosette like structure with central eosinophilic amorphous material. Varying sized duct like spaces lined by low columnar cells are present within the nodules. Fragments of crystalline calcification resembling cementum may be seen. Presence of amyloid like material resembling to that of CEOT has led some workers to propose the existence of combined AOT and CEOT. However, Montes et al concluded that CEOT like areas were within normal histopathological spectrum of AOT. The calcified materials seen in adenomatoid odontogenic tumor have been considered to be a form of enamel,dentin, enamel and dentin, cementum, dentin and cementum or dystrophic calcifications, but their exact nature still remains a controversy [15].

Immunohistochemical studies of the lesion suggest expression of keratin and vimentin in the tumor cells at the periphery of the ductal, tubular, or whorled structures. Amelogenin and enamelin in small mineralized foci are found in the tumor cells and in hyaline droplets. During the last few years several studies have been published dealing with the immunhistological properties of AOT. Immunohistochemically, the classical AOT phenotype is characterized by a cytokeratin (CK) profile similar to follicular cyst and/or oral or gingival epithelium based on positive staining with CK5, CK17 and CK19. On the other hand the classical AOT is negative for CK4, 10, 13 and 18. Recently, the expression of cytokeratin 14 in AOT was detected and it concluded that this probably indicate its origin in the reduced dental epithelium which is also positive for staining with cytokeratin 14 antibodies. Positive reactions for amelogenin in limited areas in AOT are also reported as well as in ameloblasts and in the immature enamel matrix. [16] Since all variants show identical benign biological behavior and almost all are encapsulated, conservative surgical excision accompanied by enucleation and curettage is the treatment of choice. Recurrence of AOT is exceptionally rare [18,20].

This report describes an unusual presentation of an extrafollicular adenomatoid odontogenic tumor in the mandible of a middle aged male patient, which is somewhat controversial to the usual presentation sited in the literature.

2. Case Report

A 43 years old male patient was presented with a hard swelling presented over the parasymphysial region of the right side mandible, extending from 43 to 45 region. There was a history of mild to moderate pain in relation to 44 tooth, for 6 months duration. It was a gradual onset, dull type of constant pain with no radiation. There was no history of trauma, discharge or any other symptoms except pain in relation to the lesion. The patient had no systemic diseases or any allergies and he was not on any medication.

Figure 1. IOPA view of the lesion

In the clinical examination of the head and neck, no lymphadenopathy was found. Facial asymmetry was not observed. There was no obvious swelling at the visual inspection. But on palpation, there was a firm swelling over the right side parasymphysial region 3x2 cm² in size, with a round shape and soft in consistency. It was associated with mild tenderness on palpation. Intra orally, there was a firm swelling from 43 to 45 region, with grade II mobility of 44 and grade I mobility of 45 & 43. The swelling had well defined margins with normal overlying mucosa. It was bony hard and tender to palpation. Periapical and occlusal radiographs showed a circumscribed apical radiolucency extending from apical region of 43 to apical region of 45 with root resorption of 44 -45. There were no radiopaque foci (Figure 1).

Figure 2. Microscopic area with the features of Adenomatoid Odontogenic Tumor

Figure 3. Higher magnification of the epithelial whorls (H&E)

According to the clinical features and radiographic findings, the possibility of an odontogenic tumor like ameloblastoma was considered preoperatively. An Excisional biopsy was taken under LA raising a mucoperiosteal flap and a decompression tube was placed. Gross examination of the specimen showed a single pink-white soft tissue measuring 3.5 x 2.0 x 1.2 cm³. Microscopy revealed a well-defined cystic tumor encapsulated with fibrous cyst wall, in part lined by odontogenic epithelium. Bilayered epithelial strands, calcifications, epithelial whorls can be seen and odontogenic epithelial rests are seen in the capsule. Elsewhere the cyst epithelium exhibits characteristic of a unicystic ameloblastoma. These histomorphological features were more suggestive of ‘Adenomatoid Odontogenic Tumor’. However the possibility of unicystic ameloblastoma couldn’t be completely excluded. (Figure 2, Figure 3).

As the patient’s management, conservative surgical excision of the tumor accompanied by enucleation and curettage was done and the patient is currently on regular follow up with no post-operative complications.

3. Discussion

Adenomatoid Odontogenic Tumour (AOT) is a slow growing lesion, constituting only 2.2-7.1% of all odontogenic tumors [4] with a predilection for the anterior maxilla relative to mandible in a ratio of 2:1, and is usually associated with impacted canines, of young females. [13] It is often referred to as “Two- Third” tumor because 2/3rd of tumors’ affect females, 2/3rd in their 2nd decade of life, and 2/3rd of tumors associated with impacted teeth in maxilla [4]. When considering the gender predisposition, even higher ratios are found in Asian populations according to the literature; the highest incidence being observed in Sri-Lanka (3.2:1) [17] and Japan. (3:1) [14]. But our case is controversial to the literature in all the above mentioned aspects because this AOT was reported in a middle aged male, in the parasymphysial region of the mandible, which was not associated with an impacted tooth (Table 1).

Table 1. unusual findings seen in our case related to the available literature

According to the literature, AOT normally produces a slow swelling not accompanied by pain. [6] With the growth of the intraosseous variant, cortical expansion may occur which may give rise to a palpable bony-hard swelling with or without slight pain. Tumor growth will cause displacement of teeth due to the expansion of the surrounding bone, rather than root resorption.7 But in the present case, pain in relation to a premolar in the right side mandible was the presenting feature of the patient. During examining for the cause of pain and mobility of the associated teeth, a palpable, bony-hard swelling with slight tenderness was noted. Root resorption of two premolars was evident in the radiograph (Figure 1).

According to the clinical presentation of the tumour, it was not strongly suggestive of Adenomatoid Odontogenic Tumor at the beginning, giving more weight towards the possibility of an ameloblastoma, which is more common in 3rd and 4th decade, in the mandible with equal gender distribution. [18] Resorption of roots of involved teeth is also a common finding in Ameloblastoma [18], compared to AOT, which usually causes displacement of the neighbouring teeth rather than root resorption [7].

The radiographic findings of AOT frequently resemble other odontogenic lesions such as dentigerous cysts, calcifying odontogenic cysts, calcifying odontogenic tumours, globulo-maxillary cysts, ameloblastomas, odontogenic nematocysts and periapical diseases. [19,20] However they are easily differentiated on histology. Whereas the follicular variant of AOT shows a well circumscribed unilocular radiolucency, associated with the crown and often part of the root of the impacted tooth, the radiolucency of the extrafollicular type is located between, above or superimposed upon the roots of erupted permanent teeth. Peripheral variant does not show any radiological features except some evidence of erosions of the adjacent cortical bone. [20] According to literature, Two thirds of the intra bony cases have scattered radiopacities within the radiolucency, [11] which was not evident in our case.

The radiolucency of our patient’s lesion was extending between left side mandibular canine and the same side second premolar. Radiological differential diagnosis for the lesion were Extrafollicular adenomatoid odontogenic Tumor, Unicystic Ameloblastoma, Calcifying epithelial odotontogenic tumor at the early stage, Calcifiying Cystic Odontogenic Tumor at the early stage and developmental lateral periodontal cyst.

Management of the patient and predicting the prognosis depends on the accurate diagnosis of the lesion. Conservative complete surgical excision of the lesion can be carried out, accompanied by enucleation and curettage for treatment of AOT. Similar management is indicated for luminal and intraluminal type unicystic ameloblastomas, whereas the mural type of unicystic ameloblastoma requires treatment in a similar way to solid multicystic ameloblastoma. [18] Mural type of unicystic ameloblastoma behaves in a more aggressive manner compared to AOT, luminal and intraluminal unicystic ameloblastomas. Therefore for the accurate diagnosis of the lesion, microscopic findings were of paramount importance.

‘Microscopically AOT is a capsulated lesion. It is composed of duct like structures and solid islands of packed elongated cells which are arranged in whorled pattern. Characteristic rosette like structures with two concentric rings of ameloblast like cells and hyaline material between the two layers are also present. The stroma is composed of irregular sparsely cellular connective tissue with calcification and hyaline material. Calcification seen in adenomatoid odontogenic tumor have been considered to be a form of enamel,dentin, enamel and dentin, cementum, dentin and cementum or dystrophic calcifications, but their exact nature still remains a controversy [15].

Similar to the literature, in the present case, microscopical features such as bilayered epithelial strands, calcifications, epithelial whorls and odontogenic epithelial rests were strongly suggestive of the diagnosis of AOT. In some areas cyst epithelium exhibited characteristics of a luminal type unicystic ameloblastoma. Even though the clinical features closely resembled an ameloblastoma than an AOT, the absence of epithelial whorls and specially calcifications in the ameloblastoma microscopically, helped to arrive at the final diagnosis of the lesion as Adenomatoid Odontogenic Tumor.

Immunohistochemical studies of the lesion suggest expression of keratin and vimentin in the tumor cells at the periphery of the ductal, tubular, or whorled structures. Amelogenin and enamelin in small mineralized foci are found in the tumor cells and in hyaline droplets. [16] However no immunohistochemical studies were carried out for diagnostic purposes, with regard to the present case.

Since all variants show identical benign biological behavior and almost all are encapsulated, conservative surgical excision accompanied by enucleation and curettage is the treatment of choice. [16,18] In the present case similar management was done and the patient is on regular follow up.

4. Conclusion

In conclusion, this report on Adenomatoid Odontogenic Tumor, draws attention on a relatively uncommon odontogenic tumor, which can be easily misdiagnosed as several other entities in the absence of proper interpretation of the history, examination and investigation findings, particularly when the tumor deviates from its common features. Even though AOT is commonly referred to as the “Two- Third Tumor”, this case report highlights the need of including it in the differential diagnosis of similar cases, where it does not exhibit even a single clinical feature corresponding to the “Two-Third Tumor” theory.

Conflict of Interest

The authors declare no conflict of interest whatsoever arising out of the publication of this manuscript.

References

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