Ⅰ. INTRODUCTION
Odontogenic keratocyst (OKC), also known as keratocystic odontogenic tumor (KCOT), is an emerging odontogenic tumor originating from the dental lamina. It is an aggressive lesion with a squamous epithelium and a recurrence rate of 15-35%.1 Radiologically, there is a clear, smooth, or shell-like border showing a unilocular or multifocal, polycystic radiographic picture. The borderline may not be clear when the lesion is infected or perforation of the associated cortical bone occurs. Hard tissue formation in OKC is a very rare phenomenon and occurs in the form of dystrophic calcification, cartilaginous tissue or dentinoid.2
This case report introduces the case of OKC with calcification and will review the related papers.
This study was reviewed by the Institutional Review Board(IRB) of Pusan National University Dental Hospital and was approved from deliberation(PNUDH-2018-028)
Ⅱ. CASE REPORT
A 71-year-old female was referred for inflammation on the left maxillary sinus. At the time of admission, there were no clinical symptoms such as pain, except for a slight edema in the left maxilla. The pus and fistula were found 1 month after the first visit.
On panoramic photographs, the maxillary left third molar displaced to the left maxillary sinus and the radiopaque image below it were seen. (Fig. 1) On the CT face (non-CE), a spherical lesion with a transparent radiographic impermeable surface with a well-defined border around the maxillary left third molar was observed. (Fig. 2) The lesion was provisionally diagnosed as Calcifying Epithelial Odontogenic tumor(CEOT) and removed under general anesthesia with one mass including the maxillary left third molar. (Fig. 3) The specimen was sent to the Department of Pathology, Pusan National University Hospital.
Histopathologically, the cystic wall resembled a squamous epithelium of multiple layers, and inflammatory cells were significantly invaded under the fibrotic wall. (Fig. 4a) Basal cells were hyperchromatic and polarized, and the rete peg disappeared overall. (Fig. 4b) Calcification was observed near the epithelial lining (Fig. 5) Based on the overall microscopic findings, we can conclude that OKC with calcification. After surgery, she is currently undergoing routine follow – up check and is well maintained without any sign of recurrence.
Ⅲ. DISCUSSION
The OKC, also known as keratocystic odontogenic tumor (KCOT), is an emerging odontogenic cyst originating from the dental lamina. In the past, this lesion was called KCOT because it was thought to have more characteristics of neoplasm rather than those of cysts. However, according to the The World Health Organization(WHO) classification of odontogenic lesions updated in 2017, there was insufficient evidence for calling neoplasm, so it is called OKC again.3 It is an aggressive lesion with a squamous epithelium and a recurrence rate of 15-35%.1 Except for infected or perforate cortical bone, most of them appear as unilocular or multilocular radiolucent lesions with clear margins. Histopathologically, OKC is highly specific. It has stratified squamous parakeratinized epithelial lining ranging from 6 to 10 cell layers thick without rete ridges. There is a welldefined, palisaded basal cell layer that is composed of columnar and cuboidal cells. Cystic cavities often show desquamated keratin.4
OKC with radiopaque lesion is very rare so it is easy to misdiagnosis as other lesion for example Calcifying odontogenic cyst, Calcifying epithelial odontogenic tumor.
Calcifying odontogenic cyst(COC), also called Gorlin cyst, Calcifying cystic odontogenic tumor, Dentinogenic ghost cell tumor, Ghost cell odontogenic carcinoma is characterized by odontogenic epithelium contiaining “ghost cells,” which then may undergo calcification. Although most are cystic, but some lesions occur as solid tumorlike growths. The central calcifying odontogenic cyst is usually a unilocular, well-defined radiolucency, although the lesion sometimes may appear multilocular. Radiopaque structures within the lesion, either irregular calcifications are present in about one-third to one-half of cases. About one-third of cases, the radiolucent lesion is associated with an unerupted tooth, most often a canine. The most specific histopathologic features of calcifying odontogenic cyst are that there are various numbers of ghost cells in epithelial components. These eosinophilic ghost cells are epithelial cells characterized by the loss of nuclei while preserving the basic cell contours. When it is enucleated, the prognosis is good.5
Calcifying epithelial odontogenic tumor(CEOT), also known as the Pindborg tumor is very rare odontogenic tumor. It is most often encounterd in patients between 30 and 50 years of age. There is no sex predilection. Its histogenesis is uncertain. Radiographically, the tumor exhibits either a unilocular or a multilocular radiolucent defect. The margins of the lytic defect are often scalloped and usually relatively well defined. The tumor is frequently associated with an impacted tooth, most often a mandibular molar. The lesion may be entirely radiolucent, but calcified structures of varying size and density are commonly seen. CEOT have heterogeneous islands, strands or polyhedron epithelial cells in fibrous stroma. The cell extensions of epithelial cells are distinct, and intercellular bridges can be pointed out. Calcifications, which are a distinctive features of the tumor, develop within the amyloidlike material and form concentric rings. (Liesegang ring calcifications) Conservative local resection to include a narrow border of surrounding bone appears to be the treatment options, although lesions in the posterior maxilla should probably be treated more agressively. A recurrence rate of about 15% has been reported. The overall prognosis appears good.4
Radiopaque lesion of OKC has usually caused dystrophic calcifications, cartilaginous tissue or dentinoid. Studies by Ng and Siar et al. reported that dystrophic calcification alone is reportedly most prevalent (22%-33.3%). Primary nonrecurrent OKC shows a slightly higher prevalence for dystrophic calcification than primary OKC that recurred. However, in recurrent OKC, dystrophic calcification is comparatively uncommon. Ng and Siar et al. reported that only 5% of recurrent OKCs have dystrophic calcification, while dystrophic calcification was found in 16% of primary nonrecurrent OKCs 6
In this case, calcified tissue was found near the epithelial lining.
Browne et al., found a high incidence of crystalline calcium phosphates, hydroxyapatite and whitlockite, and inorganic phosphates in OKC aspirated fluid. This may be responsible for the increased frequency of calcific deposits in the walls of these cysts. It was speculated that in other soft-tissue microenvironments, namely the dermis, dystrophic calcification occurs in a homogeneous matrix produced by pre-existing structures such as sweat glands, nevus cells, or even Rushton’s hyaline bodies which are structures originating from the pure epithelial or hematogenous origin that are typically found within the cyst epithelial linings and occur in about 4.6-11% of OKC. These bodies can appear in various shapes, such as straight, curved, or hairpin, and can be calcified. The hairpin-shaped deposits observed in this case belong to this category.7
The mechanism of formation of dentinoid in the cyst wall also remains unclear. An inductive effect of the odontogenic epithelial component is the favored explanation for the presence of dentin or dentinoid materials in dentin-forming odontogenic neoplasms, eg, the calcifying odontogenic cyst and the ameloblastic fibrodentinoma.8 These deposits often appeared arranged in a row to the odontogenic epithelium. The other alternative explanation is that the formation of dentin or dentinoid may represent a metaplastic change in the connective tissue. However, the stimulus triggering this metaplastic process is not known. 5
In the case of ossification, the pathological mechanism was not revealed either, but BSP (Bone sialoprotein) is considered to be the most important factor. BSP is secreted from bone, dentin and cement-forming cells and is known to be important for de novo bone formation and mineralization.9 Studies by Malaval et al. demonstrated that BSP (gene) knockout in mice displayed thinner cortical bones than the wild type mice models and suggested that BSP deficiency impairs bone growth and mineralization, with dramatically reduced bone formation.10 Expression of the BSP gene in other odontogenic tumors such as ameloblastoma is consistent with the expression of BSP by the enamel epithelium and also with the expression of BSP by neoplastic tissues, which could play a possible role in tumorigenesis. Osseous metaplastic process can also explain bone formation in OKC.11
The significance of calcification and osseous tissue formation in the biologic behavior of OKCs is not elucidated. Although the prognosis has not been studied yet, the presence of calcification does not seem to increase the recurrence rate, considering that the incidence is higher in primary nonrecurrent OKC than in recurrent OKC.
Ⅳ. CONCLUSION
OKC with radiopaque lesion is very rare, these are considered as dystrophic calcification, dentinoid formation, ossification. The incidence of dystrophic calcification in recurrent OKC is low, so it can be inferred that the recurrence rate of OKC with dystrophic calcification is lower than that of conventional OKC. However, this is also unclear because of the lack of relevant studies and the significance of dentinoid formation or cartilaginous tissue is unknown. More research is therefore required.
