Update from the 5th Edition of the World Health Organization Classification of Head and Neck Tumors: Odontogenic and Maxillofacial Bone Tumours

Abstract

The 5^th edition of the World Health Organization (WHO) Classification of Head and Neck Tumours (2022) comes out only five years after the previous edition, however it presents important updates that run in parallel with the rapid progression involving the increasingly sophisticated molecular investigation and its interpretation, some of which already have therapy-related impact. This manuscript provides an overview of the leading changes introduced in the classification of Odontogenic and Maxillofacial Bone Tumours that encompasses cysts of the jaws, odontogenic tumours, giant cell lesions and bone cysts, and bone and cartilage tumours. This is the first edition that Essential and Desirable Diagnostic Features were added for each entity, so that the most important clinical, microscopic and/or radiologic features were encapsulated and briefly highlighted. Surgical ciliated cyst was added to the group of odontogenic cysts, adenoid ameloblastoma was a newly recognized benign epithelial odontogenic tumour, and segmental odontomaxillary dysplasia was introduced in the group of fibro-osseous tumours and dysplasia. In addition, rhabdomyosarcoma with TFCP2 rearrangement, was introduced into the group of malignant jawbone tumours. The unique genetic aberrations distinguish it from other types of rhabdomyosarcomas. On the other hand, melanotic neuroectodermal tumour of infancy and osteoid osteoma were deleted from the benign bone and cartilageneous tumours, as was the hematolymphoid tumour of solitary plasmacytoma of bone. We systematically reviewed each entity in this chapter and provided important updated findings for selected topics that can further aid in the diagnostic process for challenging cases, broaden insights on the logic of the present classification, and finally, emphasize the potential that some of the molecular results may have in the near future to set new treatment approaches.

Keywords: Adenoid ameloblastoma; Bone and cartilage tumours; Odontogenic cysts; Odontogenic tumours; Rhabdomyosarcoma with TFCP2 rearrangement; Segmental odontomaxillary dysplasia; Surgical ciliated cyst; Update; WHO Classification.

Fig. 1

Surgical ciliated cyst of the edentulous R maxilla (arrow) following sinus surgery, showing a unilocular, radiolucent, well-demarcated and corticated lesion located on the anterior floor of the maxillary sinus. Inset shows cyst lining entirely composed of upper respiratory epithelium. Courtesy of Dr. Maria A. Copete, MSc, DDS, Professor, College of Dentistry, University of Saskatchewan, Canada

Fig. 2

Distribution of benign odontogenic tumours according to tissue of origin (epithelial, mixed epithelial and mesenchymal, mesenchymal), radiological appearance, peak age decade/s and frequent location. AdAM: adenomatoid ameloblastoma; AF: ameloblastic fibroma; AM: ameloblastoma; AOT: adenomatoid odontogenic tumour; CEOT: calcifying epithelial odontogenic tumour; COsF: cemento-ossifying fibroma; DGCT: dentinogenic ghost cell tumour; MetAM: metastasizing ameloblastoma; OdF: odontogenic fibroma; OdM: odontogenic myxoma; POT: primordial odontogenic tumour; SOT: squamous odontogenic tumour; UAM: unicystic ameloblastoma; mand-post: mandible posterior; max-ant: maxilla anterior; cx: complex odontoma; cd: compound odontoma

Fig. 3

Photomicrograph of a case of adenoid ameloblastoma highlighting the major histopathological features: cribriform architecture, ameloblastoma-like component (including basal palisading and reverse polarity) (arrows), duct-like structures and whorled cellular condensations reminiscent of morules (asterisk) (hematoxylin and eosin; scale bar 100µ)

Fig. 4

Giant cell lesions, Fibro-osseous lesions and bone and cartilage benign and malignant maxillofacial lesions with emphasis on peak age decade/s (each scale bar = 1 decade; thick scale/s = peak frequency) and leading genetic aberrations. ABC: aneurysmal bone cyst; ABC*: secondary aneurysmal bone cyst; CGCG: central giant cell granuloma; JTOF: juvenile trabecular ossifying fibroma; FoCD: focal cemento-ossifying dysplasia; FamFLCD: familial florid cemento-osseous dysplasia; FLCD: florid cemento-osseous dysplasia; PSOF: psammomatoid ossifying fibroma; PCD: periapical cemento-ossifying dysplasia; SBC*: secondary simple bone cyst; SOD: segmental odontomaxillary dysplasia

Fig. 5

A 48-year-old male with a lesion of the anterior maxilla. Microscopically, the tumour cells showed a bi-phasic morphology with both spindled (A) and epithelioid (B) cells (A, B—hematoxylin and eosin; scale bar 50µ). Cytogenetic study was positive for TFCP2 gene aberration and confirmed the diagnosis of TFCP2-RMS. Photomics are courtesy of Robert D. Foss, DDS, MS, The Joint Pathology Center, Head & Neck Pathology, Silver Spring, MD., USA