Pathology of the Head and Neck

112 P.J. Slootweg4tic fibromas, lesions to be discussed under the appropriateheadings (Sects. 4.4.3.1 and 4.4.3.6). Also, epithelialnests in the dental follicle that surrounds an impactedtooth and in the wall of odontogenic cysts may mimicameloblastoma. Maxillary ameloblastomas may bemistaken for solid-type adenoid cystic carcinomas (seeChap. 5).Ameloblastomas usually have swelling as the mostprominent symptom. In the maxilla, growth into theparanasal sinuses allows tumours to attain a considerablesize without causing any external deformity. Radiographically,ameloblastoma is a radiolucent lesion that isusually multilocular, the so-called soap bubble appearance,or unilocular with scalloped outlines [130].Sometimes, ameloblastomas present as soft tissueswellings occurring in the tooth-bearing areas of themaxilla or mandible without involvement of the underlyingbone. This peripheral ameloblastoma should not beconfused with intraosseous ameloblastomas that spreadfrom within the jaw into the overlying gingiva [117]. Inthe past, these lesions have also been described as odontogenicgingival epithelial hamartoma [6].Clinically, some variants differ slightly from the prototypicameloblastoma. Desmoplastic ameloblastomaoccurs more often in the anterior parts of both maxillaand mandible than the other types, which favour theposterior mandible [119]. Unicystic ameloblastoma occursat a lower mean age than the other types and oftenhas a radiographic appearance similar to a dentigerouscyst because of its association with an impactedtooth [115].Treatment of ameloblastoma consists of adequate tumourremoval including a margin of uninvolved tissue.For peripheral ameloblastoma simple excision willbe sufficient treatment [47, 115]. For unicystic ameloblastomawith the ameloblastomatous epithelium confinedto the cyst lining, enucleation is adequate therapy,but in cases of intramural proliferation, treatmentshould be the same as for the other ameloblastoma types[133]. When adequately treated, ameloblastomas are notexpected to recur. Adequate removal, however, may bedifficult to realise in maxillary cases that grow posterocranially.In that case, extension into the cranial cavitymay be fatal [103]. In rare instances, metastatic deposits,mainly to the lung, have been observed. Lesions showingthis behaviour are called malignant ameloblastoma(see Sect. 4.4.4.1).4.4.1.2 Calcifying EpithelialOdontogenic TumourICD-O:9340/0The calcifying epithelial odontogenic tumour , alsonamed Pindborg tumour occurs between the 2nd and6th 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 withample eosinophilic cytoplasm, distinct cell borders andvery conspicuous intercellular bridges. Nuclei are pleomorphicwith prominent nucleoli; cells with giant nucleiand multiple nuclei are also present (Fig. 4.15). Mitoticfigures, however, are absent. Clear cell differentiationmay occur [58]. The epithelial tumour islands as well asthe surrounding stroma frequently contain concentricallylamellated calcifications. The stroma contains eosinophilicmaterial that stains like amyloid (Fig. 4.16)[73, 181]. The presence of bone and cementum in the tumourhas also been reported [155]. There is no encapsulation.The tumour grows into the cancellous spaces ofthe adjacent jaw bone while causing expansion and thinningof the cortical bone.Due to its pronounced nuclear pleomorphism, the tumourmay be mistaken for a high-grade malignant carcinoma;the absence of mitotic figures should preventthis diagnostic error.Swelling is the most common clinical symptom ofthis tumour. Radiographically, the tumour is characterisedby a diffuse mixed radiodense and radiolucent appearance.Quite often, an unerupted tooth lies buriedin the tumour mass. Surgery consists of removal with amargin of uninvolved tissue. Recurrences are occasionallyseen, in particular with the clear cell variant [58].Cases occurring in the extragnathic gingival tissue canbe treated by simple excision as they are less aggressivethan the intraosseous ones [63].Metastatic disease is only seen in cases that combinethe appearance of a calcifying epithelial odontogenic tumourwith the presence of mitotic activity, suggestingmalignant transformation [175]. Mitotic activity has alsobeen seen in combination with perforation of corticalplates and invasion of blood vessels, both also highly unusualfor calcifying epithelial odontogenic tumours [27].Apparently, mitoses in this tumour indicate malignancy.4.4.1.3 AdenomatoidOdontogenic TumourICD-O:9300/0Adenomatoid odontogenic tumour probably representsan odontogenic hamartoma rather than a neoplasm[73, 181]. The lesion is mostly is seen in peoplein their 2nd decade. The anterior maxilla is the favouredsite and the lesion is often associated with animpacted tooth [120]. Grossly, the adenomatoid odontogenictumour is a cyst that embraces the crown ofthe involved tooth.The lesion consists of two different cell populations:spindle-shaped and columnar. The spindle-shapedcells form whorled nodules that may contain drop-