New tumour entities in the 4th edition of the World Health Organization Classification of Head and Neck tumours: odontogenic and maxillofacial bone tumours

Abstract

The latest (4th) edition of the World Health Organization Classification of Head and Neck tumours has recently been published with a number of significant changes across all tumour sites. In particular, there has been a major attempt to simplify classifications and to use defining criteria which can be used globally in all situations, avoiding wherever possible the use of complex molecular techniques which may not be affordable or widely available. This review summarises the changes in Chapter 8: Odontogenic and maxillofacial bone lesions. The most significant change is the re-introduction of the classification of the odontogenic cysts, restoring this books status as the only text which classifies and defines the full range of lesions of the odontogenic tissues. The consensus group considered carefully the terminology of lesions and were concerned to ensure that the names used properly reflected the best evidence regarding the true nature of specific entities. For this reason, this new edition restores the odontogenic keratocyst and calcifying odontogenic cyst to the classification of odontogenic cysts and rejects the previous terminology (keratocystic odontogenic tumour and calcifying cystic odontogenic tumour) which were intended to suggest that they are true neoplasms. New entities which have been introduced include the sclerosing odontogenic carcinoma and primordial odontogenic tumour. In addition, some previously poorly defined lesions have been removed, including the ameloblastic fibrodentinoma, ameloblastic fibro-odontoma, which are probably developing odontomas, and the odontoameloblastoma, which is not regarded as an entity. Finally, the terminology "cemento" has been restored to cemento-ossifying fibroma and cemento-osseous dysplasias, to properly reflect that they are of odontogenic origin and are found in the tooth-bearing areas of the jaws.

Keywords: Fibro-osseous lesions; Maxillofacial pathology; Odontogenic cysts; Odontogenic tumours; WHO classification.

Fig. 1

Calcifying odontogenic cyst. The lesion is unicystic but may show prominent luminal proliferations (a). The lining shows typical ameloblastomatous features, but ghost cells are the key diagnostic criterion for this lesion (b)

Fig. 2

Orthokeratinised odontogenic cyst is lined by orthokeratinised epithelium with a prominent granular cell layer. Unlike OKC, the basal layer is not palisaded

Fig. 3

Sclerosing odontogenic carcinoma is characterised by strands and islands of epithelium infiltrating through a sclerotic fibrous stroma (a). The full extent of the epithelial component may only become apparent after immunohistochemical staining with a cytokeratin (b)

Fig. 4

Primordial odontogenic tumour is composed of loosely cellular odontogenic mesenchyme surrounded by odontogenic epithelium (a). This resembles reduced enamel epithelium with columnar ameloblast-like cells (inset). This lesion arose in an 8-year-old girl and shows a well-demarcated radiolucency in a dentigerous relationship with an unerupted premolar tooth (b)

Fig. 5

The wall of an enucleated cyst shows a lining of ameloblastomatous epithelium, but with prominent islands of follicular ameloblastoma in the wall. Should this be regarded as a “mural type” unicystic ameloblastoma or cystic change in a conventional follicular ameloblastoma?