Orthokeratinized odontogenic cysts (OOC) are developmental odontogenic cysts arising from the remnants of the dental lamina and form a separate new entity in the WHO classification of odontogenic and maxillofacial bone tumors since 2017.
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Epidemiology
Orthokeratinized odontogenic cysts are rare accounting for about 1% of odontogenic cysts 1. They are found in a wide age range and are more frequent in men 2-4.
Associations
Orthokeratinized odontogenic cysts might be associated with an unerupted tooth.
Diagnosis
The diagnosis of orthokeratinized odontogenic cysts can be established with a combination of radiographic and histologic criteria:
- cystic bone lesion of the mandibula or maxilla
- orthokeratinized stratified squamous epithelial lining
- a fibrous uninflamed cyst wall
Clinical presentation
Orthokeratinized odontogenic cysts are often asymptomatic and found incidentally, they can also present as swelling 1.
Pathology
They are characterized by a lining of stratified orthokeratinized squamous epithelium 1.
Location
Orthokeratinized odontogenic cysts are more often found in the mandible than the maxilla 1,3. Usually, they occur as single lesions and rarely there are multiple lesions 1.
Microscopic appearance
Histologically orthokeratinized odontogenic cysts are characterized by the following features 1,4:
- five to eight-cell layer epithelium
- a prominent granular cell layer
- orthokeratinization
- flat to cuboidal basal cells without palisading
- capsular wall of fibrous connective tissue
Immunophenotype
On immunohistochemistry stains, orthokeratinized odontogenic cysts have been observed to express CK10 with variable expression of CK13 and CK14. Decreased KI67 index if compared to odontogenic keratocysts 4.
Radiographic features
Plain radiograph
Orthokeratinized odontogenic cysts have a well-defined and corticated radiolucent appearance on orthopantomogram with possible cortical expansion 1. Most lesions are unilocular and many are found in the vicinity of an unerupted tooth 4.
Radiology report
The radiological report should include a description of the following features:
- type location and size of the cyst
- unilocular or multilocular appearance
- relation to the adjacent structures and teeth and the presence of an unerupted tooth
Treatment and prognosis
Treatment consists of enucleation. Prognosis is excellent with very low recurrence rates of less than 2% 1-4.
History and etymology
Orthokeratinized odontogenic cysts were identified by the American oral pathologist John M Wright as an orthokeratinized variant of odontogenic keratocyst in 1981 3-6. However, the cyst was probably first described by the French physician Maurice Jeannel of Toulouse in 1886 5.
Differential diagnosis
The differential diagnosis of orthokeratinized odontogenic cysts include the following 1,4: