Case Report A Case Report of Primordial Odontogenic Tumor That Required Distinction from a Dentigerous Cyst Sawako Ono 1,*, Hotaka Kawai 2, Shintaro Sukegawa 2,3 , Kiyofumi Takabatake 2, Keisuke Nakano 2, Hitoshi Nagatsuka 2 and Tadashi Yoshino 4 1 Department of Pathology, Okayama University Hospital, Okayama 700-0914, Japan 2 Department of Oral Pathology and Medicine, Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Okayama University, Okayama 700-8558, Japan; [email protected] (H.K.); [email protected] (S.S.); [email protected] (K.T.); [email protected] (K.N.); [email protected] (H.N.) 3 Department of Oral and Maxillofacial Surgery, Kagawa Prefectural Central Hospital, Takamatsu 760-0065, Japan 4 Department of Pathology and Medicine, Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Okayama University, Okayama 700-8558, Japan; [email protected] * Correspondence: [email protected]; Tel.: +81-86-235-6651; Fax: +81-86-235-6654 Abstract: Primordial odontogenic tumor (POT) is a rare odontogenic tumor characterized by a variably cellular loose fibrous tissue with areas similar to the dental papilla and covered by cuboidal to columnar epithelium. We herein report a case of POT in a 14-year-old boy. Computed tomography (CT) exhibited a round cavity with a defined cortical border circumscribing the tooth of the second molar. However, the gross finding was a solid mass, not a cyst. Histologically, the tumor consisted of dental papillalike myxoid connective tissue covered by columnar epithelium. Therefore, although the clinical diagnosis was dentigerous cyst (DC), we diagnosed POT based on histologic findings. Clinical findings of POT resemble DC, but the clinical behavior of POT is different to DC, such as Citation: Ono, S.; Kawai, H.; cortical expansion and root resorption of teeth. Therefore, histological differentiation of POT from Sukegawa, S.; Takabatake, K.; DC is critical for accurate diagnosis. Nakano, K.; Nagatsuka, H.; Yoshino, T. A Case Report of Primordial Keywords: primordial odontogenic tumor; dentigerous cyst; odontogenic tumor Odontogenic Tumor That Required Distinction from a Dentigerous Cyst. Reports 2021, 4, 4. https://doi.org/ 10.3390/reports4010004 1. Introduction Academic Editor: Ivana Kholová A primordial odontogenic tumor (POT) is a recently described tumor, which is clas- Received: 7 January 2021 sified as a benign, mixed odontogenic tumor in the fourth edition of the World Health Accepted: 8 February 2021 Organization classification of Head and Neck Tumors in 2017 [1]. Radiologically, POT Published: 9 February 2021 demonstrates a well-defined jaw lesion with the involved tooth. It has been often clinically diagnosed as a dentigerous cyst (DC) [2]. However, as POT may cause cortical expansion Publisher’s Note: MDPI stays neutral with displacement and root resorption of neighboring teeth [3], distinguishing between DC with regard to jurisdictional claims in and POT is important. To date, no reports have described the difference between POT and published maps and institutional affil- DC. Therefore, histological and immunohistochemical differences between POT and DC iations. are not clear. Here, we report a case that was clinically diagnosed as DC but was diagnosed to be POT by histological and immunohistochemical findings. 2. Case Report Copyright: © 2021 by the authors. A 14-year-old boy with a history of retarded permanent tooth eruption visited the Licensee MDPI, Basel, Switzerland. Department of Oral and Maxillofacial Surgery, Kagawa Prefectural Central Hospital, in This article is an open access article February 2018. Computed tomography (CT) exhibited a round cavity with a defined distributed under the terms and cortical border circumscribing the tooth of the second molar (Figure1). Thus, we clinically conditions of the Creative Commons suspected DC. Macroscopically, the lesion was a well-defined, white nodule measuring Attribution (CC BY) license (https:// 10 × 7 × 3.5 mm (Figure2). Histologically, most of the tumor was composed of cellular creativecommons.org/licenses/by/ loose fibrous connective tissue with a myxoid extracellular matrix and the surface was 4.0/). Reports 2021, 4, 4. https://doi.org/10.3390/reports4010004 https://www.mdpi.com/journal/reports Reports 2021, 4, x FOR PEER REVIEW 2 of 9 Reports 2021, 4, 4 2 of 9 10 × 7 × 3.5 mm (Figure 2). Histologically, most of the tumor was composed of cellular loose fibrous connective tissue with a myxoid extracellular matrix and the surface was covered by columnar epithelium. In the fibrous tissue, spindle or stellate cells were ob- served.covered The by columnarnuclei of the epithelium. columnar epithelial In the fibrous cells were tissue, arranged spindle close or stellate to the cellsbasement were membraneobserved. The and nuclei the cytoplasm of the columnar was amphoteric. epithelial cellsIn some were regions, arranged nests close of to epithelium the basement re- sembledmembrane dental and lamina, the cytoplasm in which was the amphoteric.nuclei of epithelial In some cells regions, were displaced nests of epitheliumaway from theresembled basement dental membrane lamina, and in which the cytoplasm the nuclei were of epithelial vacuolated cells (Figures were displaced 3 and 4). There away were from nothe findings basement of calcified membrane areas and such the as cytoplasm dentin formation, were vacuolated and odontogenic (Figures epithelial3 and4). Thereislands orwere cords. no findings of calcified areas such as dentin formation, and odontogenic epithelial islands or cords. Figure 1. RadiographicRadiographic findings findings of of primordial primordial odontogenic odontogenic tumor. tumor. (a) (Thea) The lesion lesion presents presents in left in side left sideof the of posterior the posterior man- mandibledible as a dentigerous as a dentigerous cystlike, cystlike, well-circumscribed well-circumscribed radiolucency radiolucency associated associated with an unerupted with an molar unerupted in computed molar intomography. computed (b) The lesion localizes around the crown of the second molar in 3D format (the lesion: purple; the second molar: blue). tomography. (b) The lesion localizes around the crown of the second molar in 3D format (the lesion: purple; the second molar: blue). Reports 2021, 4, x FOR PEERReports REVIEW2021, 4, 4 3 of 9 3 of 9 Figure 2.FigureMacroscopic 2. Macroscopic findings findings of primordial of primordial odontogenic odontogenic tumor. tumor. (a) The (a tumor) The tumor was a was white a white mass mass measuring 10 × 7 ×measuring3.5 mm. (b )10 The × 7 cut × 3.5 surface mm. was (b) aThe solid, cut not surface cystic lesion.was a solid, not cystic lesion. Immunohistochemistry revealed vimentin expression in the epithelium and mesen- chymal component, whereas syndecan-1 (CD138) and Bcl-2 were not expressed in the ep- ithelium and mesenchymal component (Figure 5). According to histological and immuno- histochemical findings, we diagnosed the patient as having POT. After the operation, the second molar erupted. Recurrence was not observed at the 11-month follow-up. Reports 2021, 4, x FOR PEER REVIEW 4 of 9 Reports 2021, 4, 4 4 of 9 Figure 3. Histological 3. Histological findings of primordialfindings odontogenic of primordial tumor. (a) Theodontogenic tumor is composed tumor. of (a) The tumor is composed of cellular myxoid connective tissue (100×). (b) Tumor cells are spindle-shaped, lack cellular atypia cellularand mitotic activity,myxoid and are connective covered by columnar tissue epithelium (100×). (200 ×(b). ) Tumor cells are spindle-shaped, lack cellular atypia and mitotic activity, and are covered by columnar epithelium (200×). Figure 4. Histological findings of primordial odontogenic tumor. Nests of epithelium resemble dental lamina, and columnar epithelial cells show reverse nuclear polarization (200×). Reports 2021, 4, x FOR PEER REVIEW 4 of 9 Reports 2021, 4, 4 Figure 3. Histological findings of primordial odontogenic tumor. (a) The tumor is composed of5of 9 cellular myxoid connective tissue (100×). (b) Tumor cells are spindle-shaped, lack cellular atypia and mitotic activity, and are covered by columnar epithelium (200×). FigureFigure 4.4. Histological findings findings of of primordial primordial odontogenic odontogenic tumor. tumor. Nests Nests of ofepithelium epithelium resemble resemble dentaldental lamina,lamina, andand columnar columnar epithelial epithelial cells cells show show reverse reverse nuclear nuclear polarization polarization (200 (200×).×). Immunohistochemistry revealed vimentin expression in the epithelium and mes- enchymal component, whereas syndecan-1 (CD138) and Bcl-2 were not expressed in the Reports 2021, 4, x FOR PEER REVIEWepithelium and mesenchymal component (Figure5). According to histological and im- 5 of 9 munohistochemical findings, we diagnosed the patient as having POT. After the operation, the second molar erupted. Recurrence was not observed at the 11-month follow-up. FigureFigure 5. 5.Immunohistochemical Immunohistochemical findings findings of primordial of primordial odontogenic odontogenic tumor. (a) Hematoxylin tumor. (a) andHematoxylin and eosineosin staining staining (200 (200×).×). (b) ( Vimentinb) Vimentin expressed expressed in the epitheliumin the epitheliu and mesenchymalm and mesenchymal cells (200×). cells (200×). Epi- Epitheliumthelium and and mesenchymal cells cells did did notexpress not express syndecan-1 syndecan-1 (c) or Bcl-2 (c ()d or) (200 Bcl-2×). (d) (200×). 3. Discussion POT is a