Ⅰ. INTRODUCTION
Odontogenic keratocyst(OKC) comprises about 10-20% of gnathic cysts1). They occur most commonly in the mandible, especially in the posterior body and ramus2). In the past, OKC was renamed as keratocystic odontogenic tumor(KCOT) because it was regarded to have characteristics more consistent of a benign neoplasm rather than those of a cyst3). However, according to the World Health Organization(WHO) classification of odontogenic lesions updated in 2017, evidence for classifying OKC as neoplasm was considered to be insufficient and was re-classified as a cyst, regaining its name as OKC1,4).
OKC shows more aggressive behavior compared to other odontogenic cysts and are known to have a higher recurrence rate depending on the type of surgical procedure5). Despite its locally destructive behavior and high recurrence rate, malignant transformation within the cystic epithelium lining of OKC is extremely rare. Carcinoma occurred from OKC was first reported by Areen et al. in 19816) and other reports have followed since7-10).
In this study, we report a case of a 50-year-old male patient who had undergone hemi-mandibulectomy and fibula free flap due to odontogenic carcinoma progressed from a known OKC.
Ⅱ. CASE REPORT
The 50-year-old male patient was referred to the local clinic because of swelling and pain in the lower right jaw. The patient had no past medical history except hypertension.
In the panoramic view taken at the first visit, scalloped appearance of radiolucent lesion with clear margin was observed in the right mandibular body and ramus area (Fig. 1). Also, impacted #48 tooth was in contact with the lesion. In the computed tomography (CT) images, an approximately 4.4cm expansile cystic lesion with cortical bone destruction at medial cortex of mandible, adjacent soft tissue swelling, fluid infiltration and facial thickening were observed (Fig. 2).
Cyst enucleation and extraction of #48 were performed under general anesthesia. The cyst lesion was sent for pathologic examination. On pathologic examination, a flat parakeratinized stratified squamous cystic epithelium was observed (Fig. 3A). The basal cells were palisaded. The pathologic diagnosis was OKC.
After surgery, the patient was checked at 1 week, 3 weeks, 1 month, and 2 months postoperatively. There were no signs of recurrence or pathologic interval changes at that period (Fig. 4A-B). At 3 months after enucleation, there were no specific symptoms complained by the patient. However, slightly increased radiolucency was observed on panoramic view in the mid-superior area of the previous surgical region (Fig. 4C).
6 months after surgery, the patient complained of swollen gingiva and severe pain on the post-surgical site. The right lower buccal and lingual gingiva observed swelling and pus discharge with surface ulceration. Increased bone destruction was observed around #47 in the panoramic view (Fig. 5). The #46, 47 teeth were extracted due to severe mobility, and an incisional biopsy was performed with the jaw lesion. Magnetic resonance imaging (MRI, Fig. 6) and Positron Emission Tomography – Computed Tomography (PET-CT) findings were consistent with a malignant tumor. Under general anesthesia, wide excision, hemi-mandibulectomy, supraomohyoid neck dissection, reconstruction of soft and hard tissue defect with fibula free flap was performed.
Pathologic examination of the lesion was observed as followed. Mixed areas of cystic epithelium and solid tumorous growth was seen. The cystic portion (Fig. 3B) has a similar architecture to OKC, in addition revealed severe cellular atypia and occasional bulbous downward growth. The solid portion was composed of tumor islands with either ameloblastic-like polarity and clear cell changes (Fig. 3C) or general squamous cell carcinoma appearances (Fig. 3D). The tumor cells were hyperchromatic and pleomorphic. After wide excision, the overall tumor cells were observed to be highly infiltrative within the jaw bone. An association with overlying oral mucosa was not confirmed and the lesion was assumed to be a primary intraosseous lesion. The final pathologic diagnosis was odontogenic carcinoma.
After surgery, the patient has undergone periodic follow-ups for a year and no signs of recurrence has been noticed.
Ⅲ. DISCUSSION
Odontogenic carcinoma is classified into five detailed types; ameloblastic carcinoma, sclerosing odontogenic carcinoma, clear cell odontogenic carcinoma, ghost cell odontogenic carcinoma, and primary intraosseous carcinoma. Our case had mixed histological features of ameloblastic carcinoma, clear cell odontogenic carcinoma and squamous cell carcinoma, which made it difficult to define it as a specific type of odontogenic carcinoma. The tumor has a cystic epitheliumlike region as well, which is not general in odontogenic carcinoma.
Odontogenic carcinoma can arise from odontogenic cysts, odontogenic tumors or de novo. Residual apical radicular cyst and dentigerous cyst are the most common odontogenic cyst known to have malignant transformation11). The presence of a cyst and contiguous carcinoma has been explained though three possible theories12): 1) individual synchronous cyst and carcinoma arosal; 2) cystic transformation of a preexisting carcinoma or 3) carcinoma arising from a preexisting cyst. This case of odontogenic carcinoma was suspected to have originated from its preceded OKC because of a few number of evidences observed in the pathological specimen. Full enucleation of the primary lesion revealed a benign cyst with no evidence of malignancy which was consistent with the benign characteristics on radiologic images. Although most of the malignant tumor, the recurred lesion, was composed of solid tumor islands, there were portions of cystic architecture that exhibited parakeratin, yet severe cellular atypia as well. Moreover, the overlying oral mucosa or gingiva sulcus epithelium, which are candidates for carcinoma development, did not display any evidence of malignancy, suggesting a primary intraosseous lesion.
Radiologic changes in post-operative regions such as increased radiolucency and irregular marginal features raise a warning signal for not only recurrence or post-infection, but malignant transformation of remnant epithelium. Although the occurrence of malignant transformation in odontogenic cyst is rare, abnormal clinical and radiologic characteristics in post-enucleated cysts or cysts confirmed by incision and still before excision should be evaluated for possible tumorous change. Multiple biopsy, specifically made at the irregular site, may benefit accurate diagnosis. The prognosis of odontogenic cysts are more superior than carcinoma, yet periodic checkups are needed to confirm complete healing.
