ORTHOKERATINIZING ODONTOGENIC CYST: CLINICAL FEATURES, RADIOLOGY AND HISTOPATHOLOGY
Author: Sanketh DS, MDS
Orthokeratinized odontogenic cyst (OOC) was first described as an orthokeratinizing variant of odontogenic keratocyst (OKC) in 1981. The basis of this distinction was the difference in its histopathology and its reduced chances of recurrence as compared to OKC, although it was not given the status of a distinct odontogenic cyst. Later in 2005, OKC was classified as a tumor considering its aggressive behaviour and growth potential, and was renamed keratocystic odontogenic tumor (KCOT). However OOC was not considered to be a part of the tumor spectrum of KCOT.
It is now known and accepted that OOC is a distinct clinic-pathologic entity on its own. In fact it has been listed as a developmental odontogenic cyst in the recent (2017) WHO classification of odontogenic cysts. Also, the WHO consensus group has removed KCOT from the odontogenic tumor category and has re-classified it as an odontogenic cyst. They consider there is insufficient evidence for OKC to be considered a neoplastic odontogenic tumor.
So why is OOC considered to be a distinct odontogenic cyst and not a variant of OKC? Though OOC may resemble OKC clinically and histologically, there are quite a few differences that make OOC stand out.
1. OOC is not clinically aggressive and has a low rate of recurrence of 4%. This is in contrast to OKC which shows destructive behaviour and has a high rate of recurrence. Reports indicate OKCs to have an average recurrence rate of 28-30%.
2. Another distinction between the two cysts is the non-association of OOC with nevoid basal cell carcinoma syndrome otherwise called Gorlin syndrome. At least 90% of patients with Gorlin syndrome manifest with multiple OKCs. However there have not been records of any association of OOC with Gorlin syndrome.
3. Most OKC patients are asymptomatic and show no swelling of the jaws. This is attributed to the antero-posterior growth pattern of OKC as opposed to a bucco-lingual expansion. OOCs are significantly associated with swelling of jaws as compared to OKCs.
4. Almost 2/3rds (68%) of OOCs are associated with an unerupted tooth mimicking a dentigerous cyst in the radiograph. It is reported that only 25-40 % of OKCs may be associated with an unerupted tooth.
5. OOCs have a slight male predilection, mostly affect individuals in their 3rd decade and predominantly affect the mandibular posterior area, similar to OKCs.
OOCs are predominantly unilocular lesions (93%) with 68% OOCs associated with unerupted teeth in a dentigerous cyst like fashion.
Under the microscope, OOC show quite a few differences from OKC. The epithelial lining in OOC is orthokeratinized stratified squamous and has onion-skin like luminal keratinization. This is in contrast to OKC which has a parakeratinized lining. OOC has a granular layer with prominent keratohyaline granules and cuboidal to flat basal cells with no nuclear palisading or reverse polarization. On the other hand, OKC does not have a prominent granular layer and has cuboidal to columnar basal cells with nuclei oriented away from the basement membrane.
TREATMENT AND PROGNOSIS
OOC is not an aggressive lesion and is usually treated conservatively by enucleation and curettage. The prognosis for OOC is very good and has low recurrence rates of 2-4%. OOC has not been reported to be associated with NBCCS/Gorlin syndrome.
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