Odontogenic keratocysts (OKC), previously known as keratocystic odontogenic tumours (KCOT or KOT), are 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 cystic 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 KOTs will be present: an associated condition such as basal cell naevus 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 keratocystic odontic tumours), or maxilla comprising 5-10% of all jaw cysts. There may be male predilection.
Commonly discovered incidentally. When symptomatic, jaw swelling and pain are a common symptoms associated with these tumours 8. Less commonly, trismus and paraesthesia may occur.
Gross specimen examination reveals a thin-walled, friable cyst containing fluid and debris. Viscosity of the contents ranges from straw-coloured 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 characterisation.
basal cell naevus syndrome (or Gorlin-Goltz syndrome)
- strong association
- consider the diagnosis if multiple KOTs are present
- Marfan syndrome
- Noonan syndrome
Typically seen as a solitary, radiolucent, unilocular, expansile lesion with smooth, corticated borders 5. Three quarters of lesions are located in the posterior mandible. When in the mandible, they typically grow along the length of the bone in anteroposterior dimension. In the maxilla, they expand into the maxillary sinus. They average 3 cm in size.
They can be associated with or displace a crown of an unerupted/impacted tooth, mimicking a dentigerous cyst. Keratocystic odontogenic tumours can result in splaying and sometimes erosion of the adjacent tooth roots. They may occasionally appear septated, making the distinction from ameloblastoma difficult.
Reminiscent of plain radiographic findings, but in better detail. Visualised as an expansile, cystic lesion with scalloped, well-corticated borders. Density of cystic contents varies with viscosity. Cortical breach suggests possible soft tissue involvement.
Keratocystic odontogenic tumours 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
Treatment and prognosis
They are locally aggressive. Treatment is often with enucleation/excision +/-aggressive curettage. However, they can have a very high recurrence rate (30-60%), and follow-up is essential.
History and etymology
It was first described by H.P. Philipsen in 1956 as an odontogenic keratocyst.
Imaging differential considerations include:
- dentigerous cyst if pericoronal
- calcifying odontogenic cyst (Gorlin cyst) and other odontogenic (e.g. periapical) cysts and tumours
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Lucent lesions of the jaw