Odontogenic Keratocyst

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  • 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

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

  1. El-Naggar AK, Chan JK, Grandis JR. WHO classification of head and neck tumours. 2017. ISBN: 9789283224389

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