Odontogenic Keratocyst
- Benign but aggressive intraosseous lesions of odontogenic origin
- Reclassified back to odontogenic keratocyst in the WHO 2017 classification (previously classified as keratocystic odontogenic tumour [KCOT] from 2005 to 2017)[1]
Epidemiology
- Account for 5-10% of jaw cysts
- Peak incidence 20-30yrs
- ♂ > ♀ (slightly)
- Commonest site — angle of the mandible
- 70-80% occur in the mandible
- 50% at the angle of the mandible
Clinical Features
- Clinical features
Differential Diagnosis
- Differential Diagnosis
Aetiology and Pathogenesis
Aetiology
- Developmental cyst - arises from dental lamina and its remnants (cell rests of Serres)
- Can be sporadic or syndromic
- Syndromic cases:
- Associated with mutation/inactivation of PTCH gene (which activates SHH pathway)
- 5% occur as part of Nevoid basal-cell carcinoma syndrome (Gorlin-Goltz Syndrome)
Pathogenesis
- Mutation of PTCH
- PTCH is a tumour suppressor gene that encodes the PTCH protein
- PTCH protein is a receptor for sonic hedgehog (SHH)
- In adult tissue, SHH plays a role in cell cycle regulation (SHH dysfunction is implicated in various cancer types)
- ↓ PTCH gene activity → release of the break on cell cycle (mediated by SHH) → ↑ proliferative activity in epithelial lining of keratocysts
- This increase in proliferative activity causes enlargement of the cyst by mural growth (as opposed to osmotic growth seen in other cysts)
- Increase in proliferative activity may also contribute to recurrence rates
- Mural growth of cysts
- Growth is by extension of finger-like processes into marrow spaces rather than by expansion
- Growth of the wall is faster than the expansion of cyst cavity ∴ the lining becomes folded
- Cyst enlarges slowly along the pathway of least resistance
Investigations
Laboratory Investigations
Aspiration may be helpful for protein content (biochemistry) and keratinization (cytology)
Imaging
Radiographically usually multilocular 40% in a ‘dentigerous’ position
Histopathology
Lined by ortho- (10%) or parakeratinized (83%) epithelium (7% have both)— fluid has protein content <4g/ dL Histologically high mitotic activity: growth is neoplastic with invasion of the medulla and not by bony expansion
Management
- Management
Treatment = enucleation ± Carnoy’s solution (decreases recurrence)
Prognosis and Complications
- Prognosis and Complications
Follow-up
Satellite cysts or daughter cysts increase the likelihood of recurrence, as does an association with Gorlin– Goltz syndrome Orthokeratinizing keratocysts are much less aggressive. Review for recurrence (up to 60%) particularly in Gorlin– Goltz syndrome
References
- ↑ El-Naggar AK, Chan JK, Grandis JR. WHO classification of head and neck tumours. 2017. ISBN: 9789283224389
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