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tic fibromas, lesions to be discussed under the appropriate headings (Sects. 4.4.3.1 and 4.4.3.6). Also, epithelial nests in the dental follicle that surrounds an impacted tooth and in the wall of odontogenic cysts may mimic ameloblastoma. Maxillary ameloblastomas may be mistaken for solid-type adenoid cystic carcinomas (see Chap. 5).

Ameloblastomas usually have swelling as the most prominent symptom. In the maxilla, growth into the paranasal sinuses allows tumours to attain a considerable size without causing any external deformity. Radio-graphically, ameloblastoma is a radiolucent lesion that is usually multilocular, the so-called soap bubble appearance, or unilocular with scalloped outlines [130].

Sometimes, ameloblastomas present as soft tissue swellings occurring in the tooth-bearing areas of the maxilla or mandible without involvement of the underlying bone. This peripheral ameloblastoma should not be confused with intraosseous ameloblastomas that spread from within the jaw into the overlying gingiva [117]. In the past, these lesions have also been described as odon-togenicgingival epithelial hamartoma [6].

Clinically, some variants differ slightly from the pro-totypic ameloblastoma. Desmoplastic ameloblastoma occurs more often in the anterior parts of both maxilla and mandible than the other types, which favour the posterior mandible [119]. Unicystic ameloblastoma occurs at a lower mean age than the other types and often has a radiographic appearance similar to a dentig-erous cyst because of its association with an impacted tooth [115].

Treatment of ameloblastoma consists of adequate tumour removal including a margin of uninvolved tissue. For peripheral ameloblastoma simple excision will be sufficient treatment [47, 115]. For unicystic amelo-blastoma with the ameloblastomatous epithelium confined to the cyst lining, enucleation is adequate therapy, but in cases of intramural proliferation, treatment should be the same as for the other ameloblastoma types [133]. When adequately treated, ameloblastomas are not expected to recur. Adequate removal, however, may be difficult to realise in maxillary cases that grow postero-cranially. In that case, extension into the cranial cavity may be fatal [103]. In rare instances, metastatic deposits, mainly to the lung, have been observed. Lesions showing this behaviour are called malignant ameloblastoma (see Sect. 4.4.4.1).

4.4.1.2 Calcifying Epithelial Odontogenic Tumour

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The calcifying epithelial odontogenic tumour, also named Pindborg tumour occurs between the 2nd and 6th decade and mainly involves the posterior jaw area.

Also, cases located at the gingiva may be seen [63, 116].

The tumour consists of sheets of polygonal cells with ample eosinophilic cytoplasm, distinct cell borders and very conspicuous intercellular bridges. Nuclei are pleo-morphic with prominent nucleoli; cells with giant nuclei and multiple nuclei are also present (Fig. 4.15). Mitotic figures, however, are absent. Clear cell differentiation may occur [58]. The epithelial tumour islands as well as the surrounding stroma frequently contain concentrically lamellated calcifications. The stroma contains eo-sinophilic material that stains like amyloid (Fig. 4.16) [73, 181]. The presence of bone and cementum in the tumour has also been reported [155]. There is no encapsulation. The tumour grows into the cancellous spaces of the adjacent jaw bone while causing expansion and thinning of the cortical bone.

Due to its pronounced nuclear pleomorphism, the tumour may be mistaken for a high-grade malignant carcinoma; the absence of mitotic figures should prevent this diagnostic error.

Swelling is the most common clinical symptom of this tumour. Radiographically, the tumour is characterised by a diffuse mixed radiodense and radiolucent appearance. Quite often, an unerupted tooth lies buried in the tumour mass. Surgery consists of removal with a margin of uninvolved tissue. Recurrences are occasionally seen, in particular with the clear cell variant [58]. Cases occurring in the extragnathic gingival tissue can be treated by simple excision as they are less aggressive than the intraosseous ones [63].

Metastatic disease is only seen in cases that combine the appearance of a calcifying epithelial odontogenic tumour with the presence of mitotic activity, suggesting malignant transformation [175]. Mitotic activity has also been seen in combination with perforation of cortical plates and invasion of blood vessels, both also highly unusual for calcifying epithelial odontogenic tumours [27]. Apparently, mitoses in this tumour indicate malignancy.

4.4.1.3 Adenomatoid

Odontogenic Tumour

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Adenomatoid odontogenic tumour probably represents an odontogenic hamartoma rather than a neoplasm [73, 181]. The lesion is mostly is seen in people in their 2nd decade. The anterior maxilla is the favoured site and the lesion is often associated with an impacted tooth [120]. Grossly, the adenomatoid odon-togenic tumour is a cyst that embraces the crown of the involved tooth.

The lesion consists of two different cell populations: spindle-shaped and columnar. The spindle-shaped cells form whorled nodules that may contain drop-

Fig. 4.15. Nuclear atypia, ample cytoplasm and pronounced intercellular bridging are typical of a calcifying epithelial odonto-genic tumour
Fig. 4.17. Areas of small spindle cells and cylindrical cells facing extracellular material characterise the adenomatoid odontogenic tumour
Fig. 4.16. Extracellular material staining for amyloid with congo red is another characteristic feature of a calcifying epithelial odontogenic tumour

lets of eosinophilic material. A lattice of thin epithelial strands may connect these nodules to each other. The columnar cells line duct-like spaces with a lumen either empty or containing eosinophilic material and may form curvilinear opposing rows with interposed eosinophilic material (Fig. 4.17). In the stroma, there are large aggregates of eosinophilic hyaline material, which is judged to be a dysplastic form of dentin, or cementum, or to be a metaplastic reaction of the stro-mal tissue [73, 120, 181]. Also, concentrically laminated calcified bodies similar to those seen in calcifying epithelial odontogenic tumours may occur.

In some adenomatoid odontogenic tumours, areas of eosinophilic cells with well-defined cell boundaries and prominent intercellular bridges similar to those observed in the calcifying epithelial odontogenic tumour are seen [110]. They do not influence the biologic behaviour of this tumour and are considered to be part of its histologic spectrum as is the presence of melanin pigment [78, 178].

Odontogenic adenomatoid tumour usually has swelling at the site of a missing tooth as a presenting symptom. Radiographically, this missing tooth is seen surrounded by a radiolucency that may contain multiple tiny opaque foci.

Treatment consists of simple enucleation.

4.4.1.4 Squamous

Odontogenic Tumour

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Squamous odontogenic tumour is a rare lesion that mainly involves the periodontal tissues. There is no preference for either sex or jaw area [73, 181].

The lesion is composed of islands of well-differentiated squamous epithelium surrounded by mature fibrous connective tissue. There is no cellular atypia. There is spinous differentiation with well-defined intercellular bridges, but keratinisation is unusual. In the epithelial islands, cystic degeneration and calcification may occur. Invasion into cancellous bone may be present.

The absence of cytonuclear atypia rules out well-differentiated squamous cell carcinoma and the absence of peripheral palisading of columnar cells excludes ameloblastoma as an alternative diagnosis. Sometimes, intramural epithelial proliferation in jaw cysts may simulate squamous odontogenic tumour [187].

The lesion may cause loosening of the teeth involved. Radiographically, lucent areas are seen. Treatment consists of conservative removal of the tumour tissue. Occasionally, more extensive local spread may necessitate surgical excision with wider margins [142]. Sometimes, multicentric presentation may occur [79].

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