OOC occurs predominantly in the mandible and in males^4-6. These cysts are often asymptomatic and discovered as an incidental finding especially in the orthodontics’ radiographs^6,7. Here we report a case of a relatively large size OOC in the anterior region of the maxilla and a review of the previous literature.

Radiographically a unilocular radiolucent lesion with corticated borders extending from maxillary left central incisor to the right second premolar, crossing the midline, without associating any impacted tooth was seen (Figure 1). On the cone beam computed tomography (CBCT) images, lingual expansion of the mentioned area was remarkable (Figure 2). A clinical diagnosis of calcifying odontogenic cyst and KCOT was established.

The lesion was enucleated under general anesthesia and sent for the histopathologic examination. Gross examination showed a cystic lesion with elastic consistency and creamy brown colour, measuring 5.3×3.7×1.8 cm. In the microscopic evaluation a cystic lesion lined by orthokeratinized stratified squamous epithelium with prominent granular layer subjacent to the orthokeratin layer was seen. The basal layer showed little tendency of palisading. In the underlying fibrotic connective tissue wall, scattered chronic inflammatory cells infiltration and foci of hemorrhage was evident (Figure 3A,B). According to these features the diagnosis of orthokeratinized odontogenic cyst was made. After the surgery the patient was followed up. No sign of recurrence was found during one year (Figure 4).

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Figure 1: Panoramic view of the lesion shows a unilocular radiolucent lesion with corticated borders extending from maxillary left central incisor to the right second premolar.

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Figure 2: CBCT shows lingual expansion in the anterior segment of the Maxilla.

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Figure 3: A) Orthokeratinized stratified squamous epithelial lining with prominent granular cell layer (H&E; x400), B) The underlying fibrous connective tissue with scattered chronic inflammatory cell infiltration (H&E; x40).

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Figure 4: Panoramic follow up imaging shows no sign of recurrence.

Table I shows cases of OOC reported in the English case series. According to the previous studies OOC occurs mostly in the third and fourth decades of life^4,5; in line with these finding, in the present case, the patient’s age was 41. Moreover, MacDonald et al. stated that there is preponderance for female in the second decade of life. Because of the coincidence of menarche in this decade, it might be related to the hormonal element to the occurrence of the lesion in the second decade of life in women². The posterior segment of the mandible and the ramus region has been reported as the most common sites of involvement^4-6, but this case, was located in the anterior region of the maxilla with crossing the midline and extension to the other side. Dong et al. reported the occurrence rate of OOC in the anterior maxilla less than 5%⁵.

OOCs are usually asymptomatic and a slow growing swelling is the most frequent presenting symptom and is occasionally accompanied by pain⁶. The rapid growth observed in our case is not a common sign. A few case studies showed that OOCs affecting East Asian groups might be more aggressive and show different signs like paresthesia⁶.

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Table I: Orthokeratinized odontogenic cysts reported in the case series

Radiographically, OOC usually appears as a well-defined solitary unilocular or multilocular radiolucent lesion^4-6. 46.7% to 68% of OCCs are associated with an unerupted tooth^5,6 and are generally diagnosed as a dentigerous cyst. The maximum diameter of the cyst ranges from 20-70 mm with the mean size of 48 mm in various articles^4,5. In the present case, the maximum diameter of the lesion was 5.3 cm.

Kasat et al. reported a case of OOC with multiple supernumerary teeth⁹. Rare cases of bilateral involvement of the mandible, dysplastic changes in the epithelial lining of the OOC, association of the OOC with the calcifying odontogenic cyst and complex odontoma have additionally been reported in the literature^10-12. Bolbaran et al. reported a case of OOC in a patient with Nevoid Basal Cell Carcinoma Syndrome¹³. The recurrence rate was about 0-4% after complete enucleation during an average period of 6.4 to 7.8 years of follow-up^4,6. This recurrence rate is completely different than the 30% or more recurrence rate associated with KCOT.

Histopathologically, OOC is a cystic lesion with an orthokeratinized stratified squamous epithelium lining and a prominent granular cell layer in varying thicknesses. KCOT and other keratinized odontogenic cysts such as gingival cyst of newborn and also dermoid cyst must be considered in the histopathological differential diagnosis. KCOT shows a regular epithelium with 5-10 layers thickness with corrugation in the surface; palisading in basal layer not present in OOC^2,14,15. Gingival cyst of the newborn shows a parakeratotic flattened epithelial lining. It occurs in the gingiva of the newborn and is not an intraosseous cyst. Dermoid cyst, however, is lined by orthokeratinized stratified squamous epithelium with a granular cell layer similar to OOC but shows skin appendages in the cyst wall and often occurs in the midline of the floor of the mouth. Immunohistochemical studies comparing KCOT and OOC have shown a higher expression of Bcl-2, Ki-67, P53 and TGF-α in KCOT than OOC. These findings suggest reduced proliferative and anti-apoptotic activity in OOC^5,16,17. Besides, some differences in the keratin expression in KCOT and OOC support the difference in characteristics of these two lesions¹⁸. Zhang et al. study implied a significant difference in stromal collagen fibers of KCOT and OOC¹⁹. Roy et al. similarly reported increased activity of the stromal myofibroblasts in KCOT compared to OOC, which may explain the more aggressive behaviour of KCOT²⁰.

In conclusion, OOC exhibits distinctive clinical, histopathological and biological features that vary substantially from KCOT with a better prognosis and lower recurrence rate. It should be mentioned that other radiolucent lesions of the jaws such as dentigerous cyst, ameloblastoma and KCOT must be considered in the differential diagnosis.

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