Orthokeratinized odontogenic cyst presenting as a residual cyst.

Orthokeratinized odontogenic cyst (OOC) is a relatively rare odontogenic cyst characterized by the presence of orthokeratinized epithelial lining. Here, we reported an OOC that presented as a residual cyst at the right maxillary tuberosity in a 50-year-old female patient.

This 50-year-old female patient came for extraction of her right maxillary second molar with severe chronic periodontitis. The routine panoramic radiography was taken and showed the right maxillary second molar with severe periodontal destruction and a well-defined unilocular radiolucent lesion in the right maxillary tuberosity region (Fig. 1A). The patient said that the impacted right maxillary third molar was extracted many years ago. The clinical impression of the radiolucent lesion was a residual cyst. After discussing with the patient and obtaining the signed informed consent, the right maxillary second molar was extracted and the radiolucent lesion in the right maxillary tuberosity region was totally enucleated under local anesthesia. The removed soft tissue specimens were sent for histopathological examination. Microscopically, it showed a cyst lined by orthokeratinized stratified squamous epithelium with a prominent granular cell layer subjacent to the orthokeratin and many keratin shreds in the cystic lumen (Fig. 1B). The prominent granular cell layer was composed of one to three layers of granular cells with keratohyaline granules discovered in the cytoplasm of the granular cells (Fig. 1C and D). In addition, several daughter cysts lined by orthokeratinized stratified squamous epithelium (Fig. 1E, F, and G) and strands of odontogenic epithelial cells were noted in the fibrous connective tissue wall of the cyst (Fig. 1H). The above-mentioned characteristic findings finally confirmed the histopathological diagnosis of an OOC possibly developed from a long-term residual cyst.

Figure 1

Radiographic and histopathological photographs of the othokeratinized odontogenic cyst. (A) The panoramic radiography showed the right maxillary second molar with severe periodontal destruction and a well-defined unilocular radiolucent lesion in the right maxillary tuberosity region. (B) Low-power microphotograph showing a cyst lined by orthokeratinized stratified squamous epithelium with a prominent granular cell layer subjacent to the orthokeratin and many keratin shreds in the cystic lumen. (C and D) Medium- and high-power microphotographs exhibited one to three layers of granular cells with keratohyaline granules in the cytoplasm of the granular cells. (E, F, and G) Low-power microphotographs demonstrating several daughter cysts lined by orthokeratinized stratified squamous epithelium in the fibrous cystic wall. (H) High-power microphotograph showing a strand of odontogenic epithelium in the fibrous cystic wall. (Hematoxylin and eosin stain; original magnification; B, 4×; C, 10×; D and H, 40×; E, F, and G, 4×).

There were several specific features of the OOC. First, unlike the odontogenic keratocyst (OKC) which is lined by parakeratinized stratified squamous epithelium with a prominent palisaded basal layer of columnar epithelial cells, the OOC is lined by orthokeratinized stratified squamous epithelium with a prominent superficial granular cell layer. Second, the recurrence rate of OOC is approximately 2%, which is in marked contrast with the 30% high recurrence rate of OKC. Third, the OKC may be associated with nevoid basal cell carcinoma syndrome, but the OOC is not. The immunohistochemical stain is useful for identification of tumor cell origin, and is also helpful for differentiation of OOCs from OKCs. The expression patterns of CK10, CK13 and CK19 were studied in OOCs, epidermoid cysts, dermoid cysts, OKCs, and dentigerous cysts. It was found that the overall expression patterns of CK10, CK13 and CK19 in OOCs are similar to those in epidermoid cysts and dermoid cysts. In contrast, the overall expression patterns of CK10, CK13 and CK19 in OKCs are similar to those in dentigerous cysts.

A systematic review of 36 case series of OOCs found that OOCs occur more commonly in male patients than in female patients with a male-to-female ratio of 2 to 1. Furthermore, OOCs affect the mandible almost 2.5 times more frequently than the maxilla. All OOCs were radiolucent and 93% of them were unilocular. In addition, 68% OOCs were associated with unerupted teeth. In our case, the patient said that the impacted right maxillary third molar was extracted many years ago. Therefore, our OOC may be derived from the unremoved residual dentigerous cyst with keratinized metaplasia of the stratified squamous epithelium after a long-term stay of the residual cyst in the right maxillary tuberosity area.

Declaration of competing interest

The authors have no conflicts of interest relevant to this article.