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]
  • Subtypes:
    1. Odontogenic Keratocyst (OKC) - parakeratinised
    2. Orthokeratinised Odontogenic Keratocyst (OOKC)

Epidemiology[edit]

  • 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[edit]

  • Usually asymptomatic (commonly incidental findings)
    • When large/infected can cause pain/swelling/discharge/pathological fracture/tooth displacement/buccal expansion
  • Characteristic insidious pattern of growth
    • Unlike other cysts, OKCs do not have a high internal pressure ∴ they preferentially expand along the medullary cavity (the path of least resistance)
    • A cyst in the mandible may extend through much of the ramus and body without significant expansion of the jaw
    • Clinical signs often fail to appear until the cyst is well advanced
  • Usually solitary cysts (consider Nevoid basal-cell carcinoma syndrome (Gorlin-Goltz Syndrome))
  • High recurrence rate

Differential Diagnosis[edit]

Memory Aid - Multilocular lesions of the mandible (MACHO)
Mxyoma
Amelobastoma
Central giant cell tumour
Haemangioma/vascular malformation
Odontogenic Keratocyst

Aetiology and Pathogenesis[edit]

Aetiology[edit]

Pathogenesis[edit]

  • 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 is said to be "neoplastic")
    • 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[edit]

Unilocular odontogenic keratocyst
Large multilocular odontogenic keratocyst
Intermediate magnification of an odontogenic keratocyst showing a folded cyst.
High magnification of an odontogenic keratocyst.


Laboratory Investigations[edit]

Aspiration of cyst contents may be helpful for analysis of protein content (biochemistry) and keratinization (cytology)

Imaging[edit]

Plain film[edit]

  • Well defined radiolucent area with a sharply demarcated and corticated bony wall
  • Radiographically usually multilocular
    • Unilocular lesions tend to have a scalloped margin
    • When multilocular, can mimic ameloblastoma if many locules exist
  • Can mimic other cysts
    • 40% in a ‘dentigerous’ position
  • Adjacent roots/teeth may become displaced by large cysts, but usually the cyst will extend around the roots and inferior alveolar nerve without displacing them or causing significant expansion

Computed Tomography[edit]

  • Can facilitate diagnosis, and 3D characterisation for surgical planning

Histopathology[edit]

  • Biopsy is the diagnostic investigation of choice (OKCs have a consistent and unique appearance)
  • Features:
    1. Epithelium
      • Regular stratified squamous epithelium
      • 5-8 cells thick
      • Palisaded basal layer (cells are columnar in shape)
      • Lack rete ridges
      • Often have artifactual separation from basement membrane
      • Corrugated surface which can be parakeratinized (83%), orthokeratinized (10%) or both (7%)
    2. Thin fibrous capsule
    3. Satellite (daughter) cells
      • Particularly seen in those with NBCCS
    4. Cyst contents
      • Fluid has protein content <4g/ dL
    5. High mitotic activity
    6. Inflammatory changes
      • Inflamed cysts show hyperplastic epithelium which is no longer characteristic of OKCs and can have resemblance to radicular cysts instead
      • A larger biopsy is needed to confirm OKC if there is inflammation

Management[edit]

  • !Controversial topic¡
  • Diagnosis must be confirmed by biopsy
  • Treatment considerations:

Unilocular + small multilocular lesions[edit]

  • Conservative enucleation and bone curettage
  • Difficult to ensure all of cyst lining is removed ∵ friable capsule + complex outline of cyst
  • Epithelial remnants and satellite/daughter cysts can easily be left behind after enucleation
  • It is currently considered that enucleation alone is an inadequate form of treatment and needs to be used in combination with adjuvant methods (see below)

Large cyst extending around muti-rooted teeth[edit]

  • Difficult to completely remove, teeth may have to be sacrificed to ensure complete removal
  • May require decompression first followed by enucleation
  • Decompression is a modified marsupialization technique which causes the cyst to decrease significantly in size and the cystic lining becomes thicker resembling oral mucosa that allows for easier enucleation
  • This method decreases the levels of IL-1α which regulates epithelial cell proliferation in OKC; hence, there is immune-histochemical evidence that decompression is superior to enucleation alone

Very large cyst[edit]

  • Resection and bone reconstruction (free-flap)
  • Resection provides the least recurrences

Adjuvant treatment to enucleation[edit]

  1. Peripheral ostectomy
    • Aggressive form of adjuvant therapy where methylene blue is utilised to stain any cystic remnants and a rosehead bur is used to remove these
  2. Carnoy's solution
    • Chemical curettage that causes cell necrosis of the cystic lining
  3. Cryotherapy (liquid nitrogen)
    • Liquid nitrogen causes cell necrosis of the cystic lining

Suggested Management Protocol[edit]

Management protocol for odontogenic keratocysts (OKC). (CT: computed tomography, MRI: magnetic resonance imaging, IAN: inferior alveolar nerve, Rx: treatment, RR: recurrence rates). Image from Titinchi 2020

Prognosis and Complications[edit]

  • Recurrence:
    • High recurrence rate (up to 60%)
    • Higher in NBCCS and presence of satellite cells
    • Lower in orthokeratinised odontogenic keratocysts
Summary of recurrence rates (%) for different surgical methods in the management of odontogenic keratocysts - data from 5 large systematic reviews[2]
Study Enucleation alone Enucleation & Peri-oestectomy Enucleation & Carnoy’s solution Enucleation & cryotherapy Marsupialization/ decompression alone Decompression & residual cystectomy Resection
Al-Moraissi et al. (2017)[3] 23.10 17.40 11.50 14.50 32.30 14.60 8.40
de Castro et al. (2018)[4] 20.80 NA NA NA 18.50 11.90 NA
Chrcanovic and Gomez (2017)[5] 22.50 18.60 5.30 20.90 28.70 18.60 2.20
Johnson et al. (2013)[6] 25.60 NA 7.90 30.30 NA 15.80 6.30
Kaczmarzyk et al. (2012)[7] 26.09 18.18 50 NA 40 NA 0
Average 23.60 18.10 18.70 21.90 29.90 15.20 4.20

Follow-up[edit]

  • Yearly follow-up for at least 5 years
  • Orthopantogram every year, MRI every 2 years

References[edit]

  1. El-Naggar AK, Chan JK, Grandis JR. WHO classification of head and neck tumours. 2017. ISBN: 9789283224389
  2. Titinchi F. Protocol for management of odontogenic keratocysts considering recurrence according to treatment methods. Journal of the Korean Association of Oral and Maxillofacial Surgeons. 2020 Oct 31;46(5):358-60.
  3. Al-Moraissi EA, Dahan AA, Alwadeai MS, Oginni FO, Al-Jamali JM, Alkhutari AS, Al-Tairi NH, Almaweri AA, Al-Sanabani JS. What surgical treatment has the lowest recurrence rate following the management of keratocystic odontogenic tumor?: A large systematic review and meta-analysis. Journal of Cranio-Maxillofacial Surgery. 2017 Jan 1;45(1):131-44.
  4. [Castro MS, Caixeta CA, de Carli ML, Júnior NV, Miyazawa M, Pereira AA, Sperandio FF, Hanemann JA. Conservative surgical treatments for nonsyndromic odontogenic keratocysts: a systematic review and meta-analysis. Clinical oral investigations. 2018 Jun;22(5):2089-101.]
  5. Chrcanovic BR, Gomez RS. Recurrence probability for keratocystic odontogenic tumors: an analysis of 6427 cases. Journal of Cranio-Maxillofacial Surgery. 2017 Feb 1;45(2):244-51.
  6. Johnson NR, Batstone MD, Savage NW. Management and recurrence of keratocystic odontogenic tumor: a systematic review. Oral surgery, oral medicine, oral pathology and oral radiology. 2013 Oct 1;116(4):e271-6.
  7. Kaczmarzyk T, Mojsa I, Stypulkowska J. A systematic review of the recurrence rate for keratocystic odontogenic tumour in relation to treatment modalities. International journal of oral and maxillofacial surgery. 2012 Jun 1;41(6):756-67.