A unique case report of primordial odontogenic tumor

Introduction

The classification of head and neck odontogenic tumors is subject to constant change. More and more disease entities, distinguished on the basis of unique morphological features and processes, are added, while subtypes and variants of odontogenic tumors that are difficult to distinguish disappear. The latest version of the WHO classification from 2017 introduces two previously undescribed changes: sclerosing odontogenic carcinoma (SOC) and primordial odontogenic tumor (POT) [1, 2, 3]. Primordial odontogenic tumor (POT) belongs to the group of benign mixed epithelial and mesenchymal odontogenic tumors, due to its loose fibrous connective tissue and the cuboidal or columnar epithelium that surrounds it. Thus, the histological structure of the tumor resembles the internal epithelium of the enamel-forming organ. Randomly placed fibroblasts produce a small amount of collagen [1, 4]. There are numerous blood vessels in the abundant cellular stroma, providing a nourishing environment.
Analyzing the immunohistochemical profile of the tumor, Molina et al. suggest that the beginnings of its development are associated with the early stages of tooth germ formation. The presence of CK14, CK19 and amelogenin seems to be crucial in this theory [5]. The research of Mosqueda-Taylor et al., published long before the inclusion of POT in the WHO classification, describes 6 cases of primary odontogenic tumors. Unable to classify the changes into any of the categories at the time, the authors created the first description of the new disease entity [6]. To date, English-language literature describes 17 cases of POT. The present case report is the second in Europe and the first in Poland.

Case report

Based on a panoramic X-ray a 16-year-old patient was admitted to the Oral Surgery Department of the Medical University of Lublin due to an incidental finding in the right posterior mandible. The resorption of mandible cortical bone and extensive, multi-chamber osteolytic defect between teeth 45 and 46 measuring 20 mm × 15 mm was described in the performed CBCT imaging (Figs. 1, 2). The germ of a supernumerary tooth was visible inside the lesion. Adjacent teeth did not show any signs of resorption. The course of the inferior alveolar nerve canal was distalized with preserved bone border. The patient did not report any symptoms related to the lesion. In the extraoral examination, no abnormalities were found. Intraorally, in the vestibule of the oral cavity, there was a slight bone dilation around 46, covered with unchanged mucosa. Submandibular lymph nodes were not palpable. The patient denied any systemic diseases and denied taking any medications. Due to the lack of cooperation, he was qualified for enucleation of the tumor under general anesthesia. Initial diagnosis was made: cystis follicularis. Under general endotracheal anesthesia, aspiration puncture was performed. A turbid, white content, which did not resemble typical odontogenic cyst fluid, was obtained. After incision and elevation of the triangular mucoperiosteal flap, the alveolar processes and mandibular body of region 44-46 were visualized. Cortical bone with a diameter of about 7 mm was found to be damaged. A solid, multi-chamber change was enucleated. Supernumerary tooth 45ʹ was removed. The cavity was rinsed with antiseptic. The flap was deposited and sutured with Monosyn 4.0 resorbable sutures. The obtained tissue material was sent for histopathological examination in 10% formalin solution. The result of the examination – primordial odontogenic tumor – fulfilled the clinical criteria of this lesion. During the follow-up appointment, normal healing of the wounds was observed. Tooth 46 and 45 vitality was checked using ethyl chloride, obtaining a positive reaction. Gradual filling of the cavity and correctly reproduced bone tissue were observed on both 6- and 12-month post-op panoramic radiographs. There were no signs of recurrence.

Discussion

Primordial odontogenic tumor affects patients at a young age (min. 2, max. 19 years) [7, 8, 9]. It does not have a sex predilection, and most often occurs in the mandible (88.89%), with only two case reports showing an association with the maxillary bone [4, 10]. It is usually associated with the impacted third inferior molar. Our case is the first to involve an impacted supernumerary tooth. Due to the asymptomatic course (pain symptoms were described only in the case presented by Amer et al. and were combined with earlier marsupialization and the young age of the patient), it is incidentally found on X-rays [8]. Cone beam computed tomography (CBCT) is crucial in the correct diagnosis and treatment planning. The radiological image is described as an unilocular, less often multi-chamber, radiolucent lesion with associated impacted tooth. The classification proposed by Sun et al. organizes the relationship between the tumor and the associated tooth: type A – the POT has a pericoronal location in a dentigerous relationship; type B – the tumor appears to completely envelop an embedded tooth; and type C – the POT is in close proximity to the root of the tooth. Our case best meets the criteria of type B according to Sun et al. both in terms of tumor diameter and its location in relation to the germ of supernumerary tooth 45ʹ [11]. Due to the benign nature of the POT, simple enucleation of the tumor with the associated tooth and possible filling of the bone defect with bone substitute material seems to be an appropriate therapeutic approach. The authors strongly reject extending the procedure to include peripheral radicalization such as segmental resection of the mandible or the use of Carnoy’s solution as a method of surgical treatment, describing it as too mutilating to the patient. In all presented cases, no recurrence was observed during follow-up visits (max. 20 years). Differential diagnostics must include disease entities such as odontogenic cyst, odontogenic myxoma (OM), odontoma complex (OC) (especially in early stage of development), ameloblastic fibroma (AF), odontogenic fibroma (OF), and calcifying odontogenic cyst (COC) [1, 12, 13]. Finding the differences between primordial odontogenic tumor and odontogenic myxoma is important because of the locally malignant nature of the latter, which implies more aggressive methods of treatment. OM is associated with an impacted tooth in only about 5% of cases. Additionally, it does not have a capsule, which allows cell infiltration of the surrounding bone. Since the recurrence rate of odontogenic myxoma is quite high, this creates difficulties during the procedure of simple enucleation of the tumor, therefore requiring segmental bone resection instead [1, 14].
The development of POT includes mesenchyme proliferation similar to that of dental papilla. Immunohistochemical studies indicate the activity of epithelial and mesenchymal components during tumor histogenesis, which justifies its classification among benign mixed epithelial-mesenchymal odontogenic tumors according to the WHO classification [1, 5]. Cytokeratins CK14 and CK19 and glucose transporter (Glut-1), characteristic for human epithelial cells, were present in epithelium in all preparations. The mesenchymal component showed a significant concentration of vimentin and syndecan-1 [5]. Although Fumio et al. question the existence of POT and treat it as a histological variant of ameloblastic fibroma (AF) or odontogenic myxoma (OM), it seems that the collected material clearly documents the correctness of isolating the new disease entity [15].
However, due to the small number of described cases, further research is needed in order to articulate the characteristic clinical and histological features of the tumor to allow proper diagnosis and treatment. The authors’ own observations and analysis of published clinical cases confirm the benign nature of primordial odontogenic tumor, as well as simple enucleation of the tumor as the main method of surgical treatment of POT.
The authors declare no conflict of interests.

References