Ⅰ.INTRODUCTION
Primary intraosseous carcinoma (PIOC) is a malignant odontogenic tumor that primarily develops within the mandible or maxilla.2) It is presumably arised from remnants of the odontogenic epithelium, not oral mucosa. The tumor was first reported as central maxillary epidermoid carcinoma by Loos in 1913, and Pindborg termed primary intraosseous carcinoma in 1971. Eversole coined the term primary inraosseous squamous cell carcinoma (PIOSCC). Diagnostic criteria for PIOC include initial absence of intraoral or dermal communication or ulceration, and the absence of a distant primary tumor during a period of more than 6 months. It is subdivided into 4 types as follows: type I, PIOC exodontogenic cyst; type II, malignant ameloblsatoma (subtype A) and ameloblastic carcinoma arising de novo, exameloblastoma, or exodontogenic carcinoma (subtype B); type III, PIOC arising de novo as keratinizing (subtype A) and nonkeratinizing type (subtype B); type IV, intraosseous mucoepidermoind carcinoma.
In this report, we present PIOC arising in an odontogenic cyst related with impacted third molar of the mandible, and review the literature focusing on the type I of PIOC.
Ⅱ.Case Report
A 72-year-old man visited with an intermittent mild pain in the left retromolar pad area. It had been present for 1 month. The intraoral mucosa was intact without any specific findings in its color, texture or form. Also, no abnormal sensation of the lower lip or localized lymphadenopathy were detected on physical examination. A radiolucent unilocular lesion with a well-defined margin around the impacted third molar was revealed through a panoramic radiograph (Fig. 1). A cone-beam computed tomography scan showed that the lingual cortical plate were partially destroyed with a smooth margin (Fig. 2). Based on these findings, a tentative diagnosis of dentigerous cyst or keratocystic odontogenic tumor was clinically made without a preoperative incisional biopsy.
Under general anesthesia, an enucleation of the lesion with an extraction of the impacted tooth was performed. At surgery, the mass was easily isolated from the surrounding bone. Although the inferior alveolar and lingual nerves were exposed, that did not cause any specific problems.
Histology exhibited sheets or islands of nonkeratinizing malignant epithelial cells with minimal clear cell component in continuity with begin or dysplastic cyst lining epithelium (Fig. 3). Immunostaining for PCNA and p53 protein showed a higher percentage of positive cells and more intense staining in the carcinomatous tissues than in the benign and dysplastic lesions (Fig. 4).
Postoperative Positron Emission Tomography-Computed Tomography (PET-CT) showed no hypermetabolic areas which could be suggestive of the presence or metastasis of the lesions. However, to obtain a histological safe margin, the patient underwent the marginal mandibular resection, supraomohyoid neck dissection and reconstruction with a fibular osteocutaneous free flap. The second histopathologic examination identified no malignant cells or perineural invasion in the specimen. No evidence of recurrent or metastatic carcinoma had been revealed until 5-year follow-up after the resection.
Ⅲ.Discussion
Primary Intraosseous carcinoma primarily occurs in the jaw bones, and it is a very rare entity. It can also be considered a carcinoma which occurs in the jaw bones because of Malassez remnants or intraosseous remnants of the dental lamina5). As described herein, the only bone structure that can contain the epithelial tissue within the bone is the jaw bone. Only the jaw bones are susceptible to the occurrence of PIOC. These lesions are therefore termed as odontogenic carcinoma.
Representative symptoms of the PIOC include the pain due to the invasion of mandibular nerve. Besides, the paresthesia and swelling of lower lips and a limited mouth opening due to the muscle invasion are also the representative symptoms6). Furthermore, PIOC is characterized by a lack of notable intraoral findings such as the ulcer or fistula of oral mucosa.
According to the recent classification system of PIOC, type 1 is referred to as the odontogenic origin, type 2A is referred to as the metastasis to other areas following the origin of ameloblastoma, type 2B is referred to as the ameloblastomic carcinoma, type 3 is referred to as de novo formation of keatinizing and non- keatinizing variants of primary intraosseous carcinoma and type 4 is referred to as mucoepidermoid carcinoma7).
Risa et al. stated approximately 134 cases of PIOC including six new cases4). According to these authors, there were 82 cases of odontogenic type 1 PIOC and 52 cases of type 3 de novo formation of keatinizing and nonkeatinizing variants of PIOC. These reports well illustrate that type 1 PIOC has been developed the most prevalently. Also in the current case, a 72-year-old man developed type 1PIOC.
Particularly type 1 PIOC which is associated with an impacted tooth have been reported very rarely. Yasuoka et al. reported 16 cases of type 1 PIOC which originated from the odontogenic cyst in association with an impacted tooth7). Elo et al. placed an emphasis on the fact that the carcinoma occuring around an impacted tooth has been rarely developed1). These authors reported a case of PIOC whose radiological findings were similar to odontogenic cysts occuring around the mandibular third molar.
Histopathological findings of PIOC indicate a squamous cell carcinoma with a broad spectrum of the degree of differentiation. It has also been reported that the degree of keratinization features have a variability. In the current case, non-keratinized malignant epithelial cells were observed. Consecutively, benign and dysplastic cysts lining epithelium were also observed. In addition, PCNA (proliferative nuclear antigen) which was used in the current study has been recently employed for an assessment of the activity of tumor cells8). In the current case, an immunohistochemistry was also performed using PCNA and p53 protein. A higher staining property was noted in the cacinomatous areas as compared with benign and dysplastic lesions. A higher proportion of the benign cells was also observed.
As demonstrated through a review of the literatures, cases of PIOC occuring in association with an impacted third molar, as described in the current case, have been reported very rarely. And PIOC cannot be familiar to oral and maxillofacial surgeons. It must be noted that a misdiagnosis of PIOC with a simple cyst can be easily made in patients who present with mild symptoms or cases in which the radiological findings are similar to those of cysts.
