Abstract
Adenomatoid odontogenic tumour (AOT) is a benign tumour of odontogenic origin. The differential diagnosis of AOT is crucial in terms of surgical management. The 23-year old male patient presented in this case study was referred to the maxillofacial surgery clinic due to the incidental radiological finding of a large osteolytic lesion of the anterior mandible with a retained permanent canine at the base of the bone. Ultrasound imaging revealed the anterior surface of the tooth inside the lesion, indicating extreme thinning of the maintained cortical bone and liquid filling of the cystic lesion. Surgery revealed a bone defect with a deformed, incomplete tooth inside a granulation-like soft tissue. The tooth was extracted and the soft tissues were excavated. Healing was uneventful. Radiographic and physical investigations during long-term follow-up demonstrated complete bone remodeling. Some areas of the tumour were alpha-smooth-muscle-actin positive, indicating a myoepithelial differentiation. Differential diagnosis of AOT to other odontogenic tumours, such as ameloblastoma, is crucial for therapy. Exact morphological diagnosis avoids extensive ablative surgery.
- Adenomatoid odontogenic tumor
- AOT
- immunohistochemistry
- cytokeratin
- alpha-smooth muscle actin
- epithelial membrane antigen
Adenomatoid odontogenic tumour (AOT) is a benign tumour of odontogenic origin (1). The distinction of the entity from other odontogenic tumours has been problematic for decades, in particular from ameloblastoma, as verified by the number of terms used formerly (2). The World Health Organisation (WHO) have adapted the term ‘adenomatoid odontogenic tumor’ (3) to describe this entity, as already proposed by Philipsen and Birn (4). The current WHO classification of odontogenic tumours defines AOT as being composed of odontogenic epithelium in a variety of histoarchitectural patterns, embedded in a mature connective tissue stroma. The tumour grows slowly (1). The differential diagnosis of AOT is crucial in terms of surgical management, and local excision is adequate to relieve the patient from AOT (1-3). AOT is estimated to constitute less than 10% of odontogenic tumours (5). The increasing number of reports on AOT is probably due to improved histological diagnostics (5). This case report describes an AOT with particular reference to the clinical, radiological, histological and immunohistochemical findings.
Case Report
The 23-year-old male patient was referred to the maxillofacial surgery clinic, Eppendorf University Hospital, following the radiological findings of a retained right lower canine. X-ray had been performed following the diagnosis of a non-erupted canine with no history of tooth extraction of the right mandibular frontal teeth. The right deciduous canine was still in place. The facial appearance of the patient was inconspicuous and revealed no asymmetry. The vestibular mandibular mucosa and the alveolar process were not altered. All teeth proved to react sensitively to adequate stimuli.
Radiology. The pantomogram showed the right permanent mandibular canine to be vertically impacted in the bone below the apex of the adjacent teeth. The tooth was surrounded by a bright radiotranslucent area indicating a cyst and appeared to be developed incompletely with a reduced wide apex. The crown appeared to be enlarged compared to the mandibular synergist. However, pantomograms allow no morphometric analysis, in particular in cases with obvious differences in topography of the teeth (Figure 1). Some punctuate radiopacities could be seen scattered around the tooth's crown. The initial tentative diagnosis was dentigerous cysts with a retained and dysmorphic mandibular canine, based on the physical appearance and radiograph. However, thorough inspection of the pantomogram disclosed patchy radiopacities in the surroundings of the retained tooth indicative for an odontogenic tumour (5).
Detail of panoramic radiograph showing the right side of the mandible. The deciduous right lower canine was still in place. The roots of the adjacent teeth were completely developed and showed no resorption. The retained canine was located with the crown in the direction of tooth eruption, but the incomplete root appeared to rest in line with the basal mandibular cortex. In the region of the pericoronal radiotranslucency, a few scattered radiopacities could be seen.
Ultrasound image of the region of interest. The applicator was attached to the chin. The transcutaneously applied ultrasound trespassed the vestibular cortex and was reflected completely at the lingual cortex (lower arrow). Inside the inhomogeneous translucent cavity focal complete reflections of ultrasound indicated the vestibular apex of the canine's crown (upper arrow).
The retained tooth became visible after osteotomy and excavation of the gelatineous tissue that filled up the cavity (left). The extracted tooth appeared to be dysplastic with suggested anlage of two roots (right).
Ultrasound. The mandibular bone was imaged by ultrasound, which depicted both the lingual side of the mandible and the crown of the canine inside the cavity (Figure 2). These findings were indicative of a fluid-filled bone cavity.
Surgery. Surgery was performed under general anaesthesia. The mandible was exposed after interforaminal incision. The cortex was intact. After osteotomy, inside the cavity, a reddish, bulky layer of granular-like tissue became evident. This tissue filled the cavity and embedded the tooth completely, and was consequently excavated. The tooth was attached loosely to the basal cortex and was removed easily (Figure 3). There were no apparent infiltrations of the surrounding bones. The bone defect was filled with clotted blood. The soft tissue coverage of the mucosal defect was achieved by primary intention. Healing was uneventful. The radiographic follow-up during the subsequent 6 years revealed the completion of ossification stages and no local recurrence.
Histology. Tumour tissue was embedded in paraffin. Sections (4 μm-thick) were cut and stained with haematoxylin-eosin, PAS (periodic acid Schiff), Giemsa, Elastica van Gieson and Congo red. Histological analysis revealed cystic formation with smooth solid nodular area adjacent to the retained tooth. The solid appearing masses revealed typical findings of AOT with peripheral narrow strands of smaller cells (Figure 4) that formed net-like proliferations and cribriform structures, both at the base of nodules and between them. More superficially, two to four cell layer broad zones of fusiform cells with oval nuclei and cell cytoplasm were detected in the majority of neoplastic nodal epithelial proliferations (Figure 4). The broadest zone was formed of multiple rosette-like or tubular structures of polyedric and cuboid cells. In these areas central or intraluminal collagenous, acellular material containing cementicles were detected, rarely reaching the luminal surface of nodules. The latter were mostly rounded and empty; however, some of them contained dark eosinophilic acellular material containing cement. In the center of a minority of neoplastic nodules the last type darker smaller oval to spindle cells with rounded nuclei and eosinophilic cytoplasm were found. Cellular atypia or hyperchromasia was observed. Rare mitotic figures were found (fewer than 1 per 10 high-power field).
Nodular epithelial odontogenic tumour with typical histoarchitectural pattern: small darker rounded epithelia forming cribriform and trabecular structures were located peripherally and between the nodules. Narrow zone of fusiform cells with bright cytoplasm can be seen superficially to former. The broadest layer was formed of duct-like or rosette-like structures with focal luminal eosinophilic material. Dark eosinophilic acellular material or mineralised particles can be seen in the central lumen of neoplastic nodules (HE, magnification ×200).
Loose connective tissue stroma was oedematous with hyalinised collagen fibres in addition to multiple hyalinised blood vessel walls. Neither calcifying epithelial odontogenic tumour (CEOT)-like nor squamous epithelia-differentiated areas were found. Furthermore, no amyloid depositions were detected with Congo red staining when viewed under polarised light.
Immunohistochemistry. Immunohistochemical analyses were performed in accordance with standard protocols (Table I). The immunoreactivity was evaluated in terms of location and intensity (Table II). The intensity of the staining reaction was graded semi-quantitatively: negative (-), weak (+), moderate (++) and strongly positive (+++). Negative controls of antibody reactions were performed using the same protocol but omitting the primary antibody (6). The AOT was immunoreactive for certain cytokeratin subtypes (Figures 5 and 6), vimentin (Figure 7) and p63 (Table II). Focal areas of tumour cells were also stained after incubation with antibodies identifying epithelial membrane antigen (EMA) or α-smooth muscle actin (SMA) (Figure 8).
Antibody/target antigen, clone and supplier/dilution.
Discussion
The immunophenotype of AOT shows that a subset of tumour cells expresses a protein indicative of myoepithelial differentiation. AOT is a rare, benign, epithelial tumour, most commonly found in children and young adults (5). Both intraosseous and extraosseous growth types are observed. The subtyping of AOT is based on clinical and radiological findings (Figure 9). The follicular type, where the tumour is localised around the crown of a retained tooth, is by far the most frequent growth type of AOT (5). In some cases, a marginal part of AOT may cover the upper part of the dental root. In the case presented in this case study the soft, but solid tumour covered the tooth completely, giving access to the hard tissue after enucleation of the cavity (Figure 3B). The gross macroscopic appearance of the tumour was in accordance with former definitions of the entity recommended by the WHO (3, 5).
The intraosseous follicular variant of AOT showed a well-delineated, uni-locular radiolucency sourrounding the crown of a retained tooth on radiographs. This figure was indistinguishable from follicular cysts (Figure 1). Indeed, the radiological findings of AOT are non-specific and share characteristics with other odontogenic lesions; dentigerous cyst, calcifying odontogenic cyst or tumour, ameloblastoma, keratocystic odontogenic tumor or periapical disease (7). Minute radiopacities around the retained tooth may be found in AOT cases and are considered a characteristic but not pathognomonic finding (5). About 2 out of 3 AOT cases show a distinct radiopaque calcification of radiograms (8).
Distribution of antigen-antibody reactions in defined regions of AOT.
Immunreactivity of AOT for CK14 (magnification ×100).
The case of AOT presented here demonstrated immunohistochemical findings which coincided with published analyses. Immunohistochemistry is recommended for research purposes but not as a routine tool to establish diagnosis of odontogenic tumours, including AOT (8). It has to be kept in mind that the histological diagnosis of AOT is still based on conventional staining. An earlier report pointed out that AOT phenotype is characterised by a cytokeratin profile resembling follicular cysts and gingival epithelium (9). This comparison was based on the known AOT-immunoreactivity for cytokeratin subtypes, which shows some zonal differences within neoplastic nodules. In the present case, immunoreactivity for cytokeratins and focal co-expression of vimentin and, surprisingly, also of smooth muscle actin at the base of the broad duct-like zones was found. The co-expression of vimentin pointed to the neoplastic nature of the entity and is in accordance with earlier immunohistochemical analyses on AOT (10, 11, 12, 13). Vimentin co-expression can be as high as 69.2% and is restricted to tumour cells at the periphery of ductal, tubular and whorled structures. Mineralised and hyaline material does not show immunohistochemical reactivity for cytokeratin (12). The co-expression of cytokeratin and vimentin of oral epithelia in vitro is well known (14). The proliferation rate of AOT in terms of Ki-67 positive tumour cells is low in general (9, 12, 13) and counted for fewer than 2% of nuclei in present case.
Immunreactivity of AOT for CK18 (magnification ×100).
Immunreactivity of AOT for vimentin (magnification ×100).
A minority of cells of the basal duct-like structures and probably a few of the fusiform epithelial cells showing a positive reaction against α-smooth muscle actin (target antigen: α-SMA, magnification ×100).
Schematic drawing of AOT topography in relation to teeth as the lesion may appear on orthopantomograms (adapted from Reichart and Philipsen (5), with slight modifications). The intraosseous follicular variant (F) is the most frequent type of AOT (and found in this case). The extent of tumourous coverage of the root varies but does not exceed the coronal third of the root. On the contrary, the association of tumour and tooth root of the extrafollicular type is not as close: E1 indicates that there is no relation of tumour to tooth. E2 indicates interradicular localised tumour with expansive growth (divergence of roots), E3 indicates superimposed tumour on the root apex and E4 indicates superimposed tumour on the midroot level. An extraosseous and peripheral type of AOT (P) appears like an epulis and may be associated with superficial erosion of the bony crest.
The detection of focal α-SMA-positive basal duct-like cells may indicate myoepithelial differentiation of a small population of cells within the variety of histoarchitectural patterns in AOT, characterised by positivity for p63, CK14 and α-SMA. In the case presented here, a focal loss of immunhistochemical reactivity was seen for cytokeratin 5/6, cytokeratin 14 and p63 in the most superficial epithelial tumour cells. Some of these cells reacted with epithelial membrane antigen.
Recent reviews on AOT suggest the frequency of this entity among odontogenic tumours in the range of 0.6% to 38.5% (1). AOT is about twice as frequent for females as for males. About 88% of patients were in their second or third decade of life. The follicular variant is found in about 71% of all AOT (Figure 8, (1)). The predominance of the maxilla in AOT cases is evident (64.3%). About 60% of follicular AOT are associated with a retained maxillary canine (5). AOT are extremely rarely seen associated with retained wisdom teeth (2.8%) (1, 5).
Conservative surgical intervention, such as enucleation or curettage, is the treatment of choice. Recurrence of AOT is exceptionally rare (5). Recent reports from different continents refer to possible regional differences in the prevalence of AOT (1, 15-17).
Conclusion
AOT is a rare benign epithelial odontogenic tumour preferentially arising in the jaws. AOT can be treated by local excision. Thorough morphological diagnosis is mandatory to establish the differential diagnosis, in particular diagnosis of ameloblastoma, in order to prevent extensive surgery. Immunohistochemical investigations validate the cytoskeletal characteristics that this entity shares with odontogenic cysts. The identification of α-SMA in a small population of tumour cells points to a myoepithelial differentiation of a subset of the tumor cells.
Footnotes
- Received August 19, 2009.
- Revision received April 19, 2010.
- Accepted April 21, 2010.
- Copyright© 2010 International Institute of Anticancer Research (Dr. John G. Delinassios), All rights reserved
