Pathology of the Head and Neck

114 P.J. Slootweg4Fig. 4.18. Odontogenic myxoma is composed of poorly cellularmyxoid material that surrounds pre-existing jaw boneFig. 4.19. Odontogenic fibroma consists of fibrous areas containingepithelial odontogenic nests4.4.2 Odontogenic Tumours –MesenchymalMesenchymal odontogenic tumours are derived fromthe ectomesenchymal part of the tissues that participatein the development of teeth and periodontal tissues.Odontogenic epithelial rests may be part of the histologicpicture they show, but only fortuitously by tumourtissue-engulfed structures. They have no neoplastic orinductive potential.4.4.2.1 Odontogenic MyxomaICD-O:9320/0Odontogenic myxomas usually occur in the 2nd or 3rddecade of life, although cases occurring at a very youngor old age have been reported. It is one of the more commonodontogenic tumours [8].Myxomas consist of rather monotonous cells withmultipolar or bipolar slender cytoplasmic extensionsthat lie in a myxoid stroma. Nuclei vary from round tofusiform in appearance. Binucleated cells and mitoticfigures are present, but scarce (Fig. 4.18). Occasionally,the lesion contains odontogenic epithelial rests.They are a fortuitous finding without any diagnosticor prognostic significance. Myxoma cells are positivefor vimentin and muscle-specific actin, whereas positivityfor S-100 is controversial [82, 102, 169].Myxoma may be mimicked by dental follicle anddental papilla. Both contain myxoid areas [71, 101,165]. Dental papilla tissue can be distinguished frommyxoma by the presence of a peripheral layer of columnarodontoblasts. For both dental papilla and dentalfollicle clinical and radiographic data are decisivein avoiding misinterpretation of myxomatous tissue injaw specimens: in the first case, a tooth germ lies in thejaw area from which the submitted tissue has been takenwhereas in the second case, the tissue sample coveredthe crown area of an impacted tooth.Odontogenic myxomas occur in the maxilla as well asthe mandible and in both anterior and posterior parts.Swelling may be the presenting sign as well as disturbancesin tooth eruption or changes in position of teethalready erupted. In maxillary cases, nasal stuffiness maybe the presenting sign due to tumour growth in nasaland paranasal cavities. Radiographically, lesions show aunilocular or soap-bubble appearance.As the lesion lacks encapsulation, treatment usuallyconsists of excision with a margin of uninvolved tissue[161]. Incidentally, cases with extremely aggressive localgrowth have been reported [35].4.4.2.2 Odontogenic FibromaICD-O:9321/0Odontogenic fibroma is a controversial entity. Uncertaintyexists about the broadness of histologic spectrumthat these lesions may show, and about its distinctionfrom other fibrous jaw lesions [73, 181].Odontogenic fibroma has an age distribution of 9–80 years and occurs predominantly in females [55]. Thelesion is seen within the jaw as well as in the gingiva[32].Odontogenic fibroma consists of fibroblasts lyingin a background of myxoid material intermingled withcollagen fibres that may vary from delicate to coarse.Odontogenic epithelium, either scarce or abundant,may occur (Fig. 4.19). Only rarely is the epithelialcomponent so conspicuous that differentiation betweenodontogenic fibroma and ameloblastoma maybe difficult [66]. This histologic spectrum may expandto include cell-rich myxoid areas, a greater epithelialcomponent and varying amounts of amorphous calcifiedglobules or mineralised collagenous matrix. Tu-