Odontogenic keratocyst

Last revised by Dr Yuranga Weerakkody on 15 Jul 2021

Odontogenic keratocysts (OKC), previously known as keratocystic odontogenic tumors (KCOT or KOT), are rare benign cystic lesions involving the mandible or maxilla and are believed to arise from dental lamina. Whether these lesions are developmental or neoplastic is controversial, with the 2017 WHO classification placing it back into the developmental lesion category. They are locally aggressive and tend to recur after excision. 

On imaging, they typically appear as an expansile solitary unilocular lesion extending longitudinally in the posterior portions of the mandible. Although the majority are solitary, in 5-10% of cases multiple OKCs will be present: an associated condition such as basal cell nevus syndrome should be considered in these cases.

Predominantly in younger patients (2nd-3rd decades) 1,7 and may be seen in either the body or ramus of the mandible (~70% of all OKCs) or maxilla, comprising 5-10% of all jaw cysts. There may be a male predilection.

Commonly discovered incidentally. When symptomatic, jaw swelling and pain are common symptoms associated with these tumors 8. Less commonly, trismus and paresthesia may occur.

Gross specimen examination reveals a thin-walled, friable cyst containing fluid and debris. Viscosity of the contents ranges from straw-colored fluid to purulent and cheese-like masses.

They originate from epithelial cell rests (stratified squamous keratinizing epithelium) found along the dental lamina and periodontal margin of the alveolus of the mandible 7. Inflammation may impede histologic characterization.

They are typically seen as a solitary, radiolucent, unilocular, expansile lesion with smooth, corticated borders 5. These cortices are often scalloped around the roots of teeth. Three-quarters of lesions are located in the posterior mandible. When in the mandible, they typically grow along the length of the bone with minimal buccolingual expansion. In the maxilla, they expand into the maxillary sinus

The appearance and location can vary 10. If associated with the crown of an unerupted/impacted tooth, they can mimic a dentigerous cyst. If associated with the roots of a non-vital tooth, they can mimic a radicular cyst. If large enough, they will resorb the roots of adjacent teeth. They may occasionally appear septated, making the distinction from ameloblastoma difficult. 

Reminiscent of plain radiographic findings, but in better detail. Visualized as an expansile, cystic lesion with scalloped, well-corticated borders. Density of cystic contents varies with viscosity. Cortical breach suggests possible soft tissue involvement.

Odontogenic keratocysts will typically demonstrate 3:

  • T1: high signal due to cholesterol and keratin contents
  • T2: heterogeneous signal
  • DWI: restricts due to presence of keratin
  • T1 C+: peripheral enhancement but unlike ameloblastomas no enhancing nodular component

They are locally aggressive. Treatment is often with marsupialisation/enucleation/excision +/- aggressive curettage. However, they can have a very high recurrence rate (30-60%), and follow-up is essential.

It was first described by H.P. Philipsen in 1956 as an odontogenic keratocyst.

Imaging differential considerations include:

  • dentigerous cyst -
    • both dentigerous cysts and OKC can be positioned pericoronally.
    • dentigerous cysts tend to attach at the cemento-enamel junction (CEJ) of teeth. 
  • radicular cyst -
    • does not scallop, does not exhibit septation, and is often more expansile.
    • radicular cysts are centered at the apices of non-vital teeth.
  • ameloblastoma -
    • tend to be multilocular, more expansile, with a textbook soap-bubble or honeycomb appearance.
    • tendency for ameloblastoma to be more aggressive and cause more significant tooth resorption.
    • a long-standing OKC may mimic an ameloblastoma. 
  • ameloblastic fibroma - in younger individuals, if the lesion is pericoronal to an impacted tooth.
  • simple bone cyst in younger individuals.
    • can be challenging to differentiate, but usually simple bone cysts exhibit minimal expansion, and spare the lamina dura as well as the periodontal ligament spaces.
    • an OKC will tend to efface the lamina dura. 

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Cases and figures

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  •  Case 2
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  • Case 3
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  • Case 5
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  • Case 5: sterolithographic model
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  • Case 6
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  • Case 7
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  • Case 8
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  • Case 9: right maxillary
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  • Case 10
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  • Case 11: multiple
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  • Case 12
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  • Case 13
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