The World Health Organization Classification of Odontogenic Lesions: A Summary of the Changes of the 2022 (5th) Edition

Abstract

The 5th edition of the World Health Organization (WHO) Classification of Head and Neck Tumors opened to online access in March 2022. This edition is conceptually similar to the previous classification of odontogenic lesions. The only newly defined entity in odontogenic lesions is adenoid ameloblastoma, which is classified under benign epithelial odontogenic tumors. While not odontogenic, the surgical ciliated cyst is a new entry to the cyst classification of the jaws. In other respects, a very important change was made in the new blue books that added 'essential and desirable diagnostic criteria' for each entity to highlight the features considered indispensable for diagnosis. In this article, we review the odontogenic tumors and cysts of the jaw sections of the Odontogenic and Maxillofacial Bone Tumors Chapter, outlining changes from the 2017 WHO classification and summarizing the essential diagnostic criteria and new developments.

Figure 1

Adenomatoid odontogenic tumor. A) Axial CBCT view of right maxillary unerupted canine region showing well-defined lesion with visible internal mineralization (arrow). B) Macroscopic appearance of the same case; rounded masses showing a solid yellowish pattern on the cut surface. C) Tumor demonstrating a fibrous capsule with odontogenic epithelium in solid nodules (H&E; x40). D) At high power, duct-like structures and calcifications clearly seen (H&E; x200).

Figure 2

Calcifying epithelial odontogenic tumor. A) Cropped panoramic radiograph showing well-defined radiolucency in the left body of the mandible (arrows). B) Epithelial sheets composed of polygonal cells with mild nuclear pleomorphism (H&E; x100). C) Islands of odontogenic epithelium with focal calcification and amyloid (H&E; x100). D) Congo red stain highlights the amyloid material that showed apple green birefringence with polarization microscopy-not illustrated (Congo Red; x100).

Figure 3

Ameloblastoma. A) Cropped panoramic radiograph showing a typical expansive, multilocular radiolucency (arrows). B) Follicular pattern; islands where peripheral cells show hyperchromatic nuclei in a palisading pattern, reserve polarity and looser stellate reticulum-like or squamous change in the center (H&E; x200). C) Plexiform pattern; anastomosing cords and strands of epithelium (H&E; x100). D) Desmoplastic pattern; epithelial islands in dense stroma (H&E; x100).

Figure 4

Adenoid ameloblastoma. A) Cropped panoramic radiograph showing radiolucent and unilocular lesion with well-defined boundaries (arrows). B) Axial CBCT view of the right posterior mandible and ramus showing cortical perforation. C) Characteristic cribriform architecture with pseudocysts, duct-like structures and whorls (H&E; x40). D) Duct-like clear cells associated with dentinoid matrix (H&E; x200).

Figure 5

Cemento-ossifying fibroma. A) Cropped panoramic radiograph showing a well-defined, expansile radiolucency in the posterior mandible (arrows). B) Coronal CBCT view showing the expansion and displacement of the inferior mandibular canal (arrow). C) COF is a prototype benign fibro-osseous jaw lesion. The matrix produced can be trabecular with cellular inclusions and osteoblastic rimming like bone (H&E; x200) or D) COF often contains smaller rounder and acellular matrix similar to cementum (H&E; x200).

Figure 6

Odontogenic myxoma (A-B) vs. Dental follicle (C-D). A) Cropped panoramic radiograph showing the characteristics straight criss-crossing bony septa (arrows). B) Odontogenic myxoma; Loose myxoid tissue stroma with scattered spindle and stellate cells (H&E; x200). C) Cropped panoramic radiograph showing small radiolucency around the unerupted second premolar tooth (arrow). D) Please note the histopathologic similarity with B; there are also some rests of odontogenic epithelium that can also be seen in odontogenic myxoma (H&E; x200).

Figure 7

Ameloblastic carcinoma. A) Axial CBCT view showing marked expansion, cortical destruction and soft tissue extension (arrows). B) Follicular growth where the tumor islands resemble those of ameloblastoma (H&E; x100). C) Neoplastic cells displaying significant cytologic atypia (H&E; x200). D) Marked atypia, dyskeratosis and clear cell change (H&E; x200).

Figure 8

Primary intraosseous carcinoma-NOS arising from a keratinized odontogenic cyst. A) Cropped panoramic radiograph showing ill-defined radiolucency in the left mandibular ramus (arrows). B) Low power shows the architectural features of a cyst (H&E; x200). C) Higher powers show an invasive component with dyskeratosis (H&E; x200). D) The invasive component with cytologic features of malignancy (H&E; 400).

Figure 9

Radicular cyst. A) Cropped panoramic radiograph showing a well-defined, corticated unilocular radiolucency at the apices of endodontically treated teeth (arrow). B) Lining by non-keratinized stratified squamous epithelium with epithelial hyperplasia in a characteristic arcading pattern. Cyst wall is inflamed (H&E; x100). C) Cropped panoramic radiograph of residual cyst showing a well-circumscribed, corticated unilocular radiolucency in an edentulous area of the left mandible (arrow). D) Residual (or long-standing) cyst showing less inflamed wall and a more regular thin epithelium (H&E; x100).

Figure 10

Orthokeratinized odontogenic cyst (A-B) vs. Odontogenic keratocyst (C-D). A) Cropped panoramic radiograph showing a well-circumscribed unilocular radiolucency associated with an unerupted third molar (arrows). B) OOC is lined by a uniform stratified squamous epithelium with orthokeratosis, prominent granular cell layer and bland, unpalisaded basal cells (H&E; x200). C) Cropped panoramic radiograph showing a multilocular radiolucency of the left mandibular body and ramus (arrows). D) OKC is lined by a uniform stratified squamous epithelium with a corrugated surface of parakeratin and palisaded and hyperchromatic basal cells (H&E; x200).

Figure 11

Calcifying odontogenic cyst. A) Cropped panoramic radiograph showing well-defined, unilocular, mixed radiolucent/radiopaque lesion with distinct cortical expansion of the left posterior mandible and ramus (arrows). B) Low power shows a cystic architecture with prominent eosinophilic, polyhedral cells (ghost cells). (H&E; x200). C) Focus of ghost cells, some of which show calcification (H&E; x200). D) Characteristic ghost cells where the nucleus is lost but cytoplasmic outlines are maintained (H&E; 400).

Figure 12

Glandular odontogenic cyst. A) Cropped panoramic radiograph showing a large well circumscribed unilocular radiolucency of the right maxilla (arrows). B) Axical CBCT view showing significant cortical expansion (arrow). C) Cyst lining of variable thickness with enlarged, eosinophilic hobnail cells on the luminal surface (H&E; x100). D) Hobnail luminal cells with mucous cells and occasional clear cells (H&E; x200).

Figure 13

Surgical ciliated cyst. A) Cropped panoramic radiograph showing a well-demarcated unilocular radiolucency of the left maxilla with a history of traumatic tooth extraction (arrow). B) The cyst lined entirely by respiratory epithelium (H&E; x100). C) Intra-operative view of the case located right site of maxilla. D) This case shows hyperplastic pseudostratified ciliated columnar epithelium with mucous cells and inflamed cyst wall (H&E; x200). Awareness of this entity prevents misdiagnosis.