Pathology of the Head and Neck

Maxillofacial Skeleton and Teeth Chapter 4 119Recurrences have been documented for both the cysticand the solid variant [124, 143]. If the lesion is combinedwith an ameloblastoma, this latter component dictatesthe most appropriate therapy, which consists of surgicalexcision including a margin of healthy tissue as alreadydiscussed [124].4.4.4 Odontogenic Tumours –MalignantBoth odontogenic epithelium as well as odontogenicmesenchyme may show neoplastic degeneration, causingeither odontogenic carcinomas or odontogenicsarcomas [73, 159, 181]. All entities to be mentionedshow the clinical presentation and course as well as theradiographic appearance of an intraosseous malignanttumour.4.4.4.1 Malignant AmeloblastomaICD-O:9310/3Malignant (metastasising) ameloblastoma is an ameloblastomathat metastasises in spite of an innocuoushistologic appearance. The primary tumour shows nospecific features that are different from ameloblastomasthat do not metastasise. Therefore, this diagnosiscan only be made in retrospect, after the occurrence ofmetastatic deposits. It is thus clinical behaviour and nothistology that justifies a diagnosis of malignant ameloblastoma[181]. This definition profoundly differs fromthat given in the previous WHO classification [73]. Atthat time a malignant ameloblastoma was described asa neoplasm in which the pattern of an ameloblastomais combined with cytological features of malignancy,a definition not based on behaviour but on histology.It is obvious that disparate views on what representsa malignant ameloblastoma can give rise to confusion[41, 159]. It has to be emphasised that to avoid mixingup different entities, the term malignant ameloblastomashould be reserved for metastasising ameloblastomaswhereas the ameloblastomas with atypia shouldbe called ameloblastic carcinomas, a type of lesion tobe discussed in Sect. 4.4.4.2 [104]. Confusion may alsoarise through the use of the term atypical ameloblastomasto denote lesions with a fatal outcome for variousreasons, either metastasis, histologic atypia or relentlesslocal spread [3].Metastatic deposits of malignant ameloblastomas aremostly seen in the lung [76, 77, 159]. Apart from metastasis,malignant ameloblastoma shows no featuresthat are different from conventional ameloblastoma (seeSect. 4.4.1.1).Fig. 4.25. Ameloblastic carcinoma combines the presence of epithelialnests with peripheral palisading and cytonuclear atypia4.4.4.2 Ameloblastic CarcinomaICD-O:9270/3Ameloblastic carcinoma , an entity that has only recentlybeen recognised, is a lesion with the histologicfeatures of both ameloblastoma and squamous cellcarcinoma [42, 181]. This tumour may arise de novoor from a pre-existing benign odontogenic tumour orcyst [159].Most cases of ameloblastic carcinoma occur in themandible [30]. They show a wide age range with a meanof 30.1 years [30].Ameloblastic carcinoma is characterised by cells that,although mimicking the architectural pattern of ameloblastoma,exhibit pronounced cytological atypia andmitotic activity, thus allowing the distinction betweenameloblastic carcinoma and ameloblastoma (Fig. 4.25).Metastatic lesions are described in the lungs and in thelymph nodes [36, 151].4.4.4.3 PrimaryIntraosseous CarcinomaICD-O:9270/3Primary intraosseous carcinoma is a squamous cell carcinomaarising within the jaw, having no initial connectionwith the oral mucosa, and presumably developingfrom residues of the odontogenic epithelium [73, 181].It ranges from well to poorly differentiated [42], mainlyoccurs in the posterior mandible and is more often seenin males [190].The tumour may arise from a still recognisable precursorlesion such as the epithelial lining of an odontogeniccyst [67, 90]. Also, enamel epithelium has beendocumented as a tissue of origin [154].