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WHO classification

Author: Kelly Magliocca, D.D.S., M.P.H.

Editor-in-Chief: Debra L. Zynger, M.D.

Last author update: 2 November 2020

Last staff update: 28 February 2023

Copyright: 2004-2024, PathologyOutlines.com, Inc.

PubMed Search: WHO classification[TIAB] head and neck tumors[TIAB]

Table of Contents

Cite this page: Magliocca K. WHO classification. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/mandiblemaxillawhoclassification.html. Accessed December 29th, 2024.

Definition / general

This classification (WHO 2017) is applicable to tumors that occur throughout the head and neck, including the nasal cavity, paranasal sinuses, skull base, nasopharynx, hypopharynx, larynx, trachea, parapharyngeal space, oral cavity, mobile tongue, oropharynx, salivary glands, neck (including lymph nodes), gnathic maxillofacial bones and ear

Major updates

New entities:
- Sclerosing odontogenic carcinoma: cytologically bland epithelial malignancy with stromal sclerosis exhibiting aggressive infiltrative growth into muscle and nerve; the infiltrating epithelial component tends to be small single file cords and strands which can be difficult to appreciate on routine sections and is best demonstrated with cytokeratin immunohistochemistry
- Primordial odontogenic tumor: benign tumor composed of an immature variably cellular connective tissue resembling dental papilla or odontogenic ectomesenchyme; the tumor is surfaced by cuboidal to columnar epithelium resembling the inner enamel epithelium of the enamel organ
Renamed / refined entities:
- Ameloblastic carcinoma: three subtypes of ameloblastic carcinoma listed in WHO 2005 collapsed into a single entity, ameloblastic carcinoma
- Primary intraosseous carcinoma: collapsed the complex 2005 WHO classification of primary intraosseous carcinoma into a single entity, primary intraosseous carcinoma
- Ameloblastoma: classification simplified to three types, ameloblastoma, unicystic ameloblastoma and extraosseous / peripheral types
- Desmoplastic ameloblastoma: reclassified as a histologic subtype of ameloblastoma and not a unique clinicopathologic entity
- Odontogenic fibromas: previously divided into a simple type (epithelium poor) and WHO type (epithelial rich); this distinction was eliminated and odontogenic fibroma is now defined as having variable amounts of inactive looking odontogenic epithelium with or without evidence of calcification
- Cemento-ossifying fibroma: included in the 2017 classification under odontogenic tumors to distinguish it from the juvenile categories of ossifying fibroma
- Keratocystic odontogenic tumor: renamed and reclassified as odontogenic keratocyst; the working group noted evidence currently lacking to justify the continuation of 2005 designation of keratocystic odontogenic tumor
- Calcifying cystic odontogenic tumor: renamed and reclassified as calcifying odontogenic cyst in the absence of justification for classifying the lesion as neoplastic
Removed entities:
- Odontoameloblastoma: now part of ameloblastoma
- Ameloblastic fibro-odontoma and ameloblastic fibro-dentinoma: now recognized as falling within the spectrum of odontoma, therefore are now classified as odontomas
Reinstated entities:
- Odontogenic carcinosarcoma included in the 2017 classification of malignant odontogenic tumors due to improved documentation confirming it as distinct
Notable updates:
- Inclusion of a classification for gnathic epithelial lined cysts is notable; such a classification has not appeared in the WHO since 1992
- Primordial cyst is not used synonymously with odontogenic keratocyst
- Orthokeratinized odontogenic cyst is recognized as distinct from odontogenic keratocyst
- Refined criteria for glandular odontogenic cyst presented
- One nonodontogenic epithelial lined cyst included in the 2017 classification: nasopalatine duct cyst

WHO (2017)

Odontogenic carcinomas ICD-O
- Ameloblastic carcinoma9270/3
- Primary intraosseous carcinoma, NOS9270/3
- Sclerosing odontogenic carcinoma9270/3
- Clear cell odontogenic carcinoma9341/3
- Ghost cell odontogenic carcinoma9302/3
Odontogenic carcinosarcoma 8980/3
Odontogenic sarcomas 9330/3
Benign epithelial odontogenic tumors ICD-O
- Ameloblastoma9310/0
  - Ameloblastoma, unicystic type9310/0
  - Ameloblastoma, extraosseous / peripheral type 9310/0
  - Metastasizing ameloblastoma9310/3
- Squamous odontogenic tumor9312/0
- Calcifying epithelial odontogenic tumor9340/0
- Adenomatoid odontogenic tumor9300/0
Benign mixed epithelial and mesenchymal odontogenic tumors ICD-O
- Ameloblastic fibroma9330/0
- Primordial odontogenic tumor
- Odontoma9280/0
  - Odontoma, compound type9281/0
  - Odontoma, complex type9282/0
- Dentinogenic ghost cell tumor9302/0
Benign mesenchymal odontogenic tumors ICD-O
- Odontogenic fibroma 9321/0
- Odontogenic myxoma / myxofibroma9320/0
- Cementoblastoma 9273/0
- Cemento-ossifying fibroma 9274/0
Odontogenic cysts of inflammatory origin ICD-O
- Radicular cyst
- Inflammatory collateral cysts
Odontogenic and nonodontogenic developmental cysts ICD-O
Malignant maxillofacial bone and cartilage tumors ICD-O
- Chondrosarcoma9220/3
  - Chondrosarcoma, grade 19222/1
  - Chondrosarcoma, grade 2 / 39220/3
- Mesenchymal chondrosarcoma9240/3
- Osteosarcoma, NOS9180/3
  - Low grade central osteosarcoma9187/3
  - Chondroblastic osteosarcoma9181/3
  - Parosteal osteosarcoma9192/3
  - Periosteal osteosarcoma9193/3
Benign maxillofacial bone and cartilage tumors ICD-O
- Chondroma 9220/0
- Osteoma 9180/0
- Melanotic neuroectodermal tumor of infancy9363/0
- Chondroblastoma 9230/1
- Chondromyxoid fibroma9241/0
- Osteoid osteoma9191/0
- Osteoblastoma9200/0
- Desmoplastic fibroma8823/1
Fibro-osseous and osteochondromatous lesions ICD-O
Giant cell lesions and bone cysts ICD-O
Hematolymphoid tumors ICD-O
- Solitary plasmacytoma of bone9731/3
ICD-O note: The first four digits indicate the specific histological term. The fifth digit after the slash (/) is the behavior code, which indicates whether a tumor is malignant, benign, in situ or uncertain (whether benign or malignant) (WHO: International Classification of Diseases for Oncology, 3rd Edition (ICD-O-3) [Accessed 28 October 2020])

Microscopic (histologic) images

Contributed by Kelly Magliocca, D.D.S., M.P.H.

Adenomatoid odontogenic tumor

Ameloblastic carcinoma

Ameloblastic fibroma

Ameloblastoma

Ameloblastoma, extraosseous / peripheral type

Ameloblastoma, unicystic type

Aneurysmal bone cyst

Calcifying epithelial odontogenic tumor

Calcifying odontogenic cyst

Cemento-osseous dysplasia

Cementoblastoma

Central giant cell granuloma

Cherubism

Chondrosarcoma

Clear cell odontogenic carcinoma

Dentigerous cyst

Dentinogenic ghost cell tumor

Desmoplastic fibroma

Fibrous dysplasia

Gingival cyst

Glandular odontogenic cyst

Inflammatory collateral cysts

Lateral periodontal cyst

Melanotic neuroectodermal tumor of infancy

Nasopalatine duct cyst

Odontogenic fibroma

Odontogenic keratocyst

Odontogenic myxoma / myxofibroma

Odontogenic sarcoma

Odontoma

Orthokeratinized odontogenic cyst

Ossifying fibroma

Osteoma

Osteosarcoma, NOS

Peripheral giant cell granuloma

Primary intraosseous carcinoma, NOS

Primordial odontogenic tumor

Radicular cyst

Simple bone cyst

Solitary plasmacytoma of bone

Squamous odontogenic tumor

Additional references

Head Neck Pathol 2017;11:68, Am J Surg Pathol 2008;32:1613, Histopathology 2014;65:606, Barnes: Pathology and Genetics of Head and Neck Tumours, 3rd Edition, 2005, El-Naggar: WHO Classification of Head and Neck Tumours, 4th Edition, 2017

Board review style question #1

Which new benign entity has been added in the 2017 WHO classification of odontogenic and maxillofacial bone tumors?

Adenomatoid odontogenic tumor
Ameloblastic carcinoma
Primordial odontogenic tumor
Sclerosing odontogenic carcinoma

Board review style answer #1

C. Primordial odontogenic tumor. Primordial odontogenic tumor is a recently recognized benign odontogenic tumor. Being exceptionally rare in the lung, it was introduced in the 2015 WHO classification of lung tumors. Adenomatoid odontogenic tumor is a benign odontogenic tumor in the WHO classification but is not a new entity in the 2017 edition. Sclerosing odontogenic carcinoma is a new entity in the 2017 WHO but is malignant. Ameloblastic carcinoma is an odontogenic malignancy and is not a new entity in the 2017 edition.

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Reference: WHO Classification of Odontogenic and Maxillofacial Bone Tumors

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