J Korean Assoc Oral Maxillofac Surg 2024; 50(3): 161~165
An unusual presentation of peripheral ameloblastoma in the maxilla
Rosa María Acevedo Ocaña1, Jorge Cortes-Bretón Brinkmann2, Carolina Valle Rodríguez1,3, Norberto Quispe López1,4, María Isabel Sánchez Jorge1
1Department of Oral Surgery, Implantology and Periodontics, Faculty of Dentistry, Universidad Alfonso X el Sabio, 2Department of Dental Clinical Specialties, Faculty of Dentistry, Universidad Complutense de Madrid, 3Doctoral Programme in Surgery and Odontostomatology, University of Alcalá de Henares, Alcalá de Henares, Madrid, 4Department of Surgery, Faculty of Medicine, Dental Clinic, University of Salamanca, Salamanca, Spain
Rosa María Acevedo Ocaña
Department of Oral Surgery, Implantology and Periodontics, Faculty of Dentistry, Universidad Alfonso X el Sabio, C. de Albarracín, 35, Madrid 28037, Spain
TEL: +34-655687062
E-mail: racevoca@uax.es
ORCID: https://orcid.org/0000-0002-5234-9402
Received January 23, 2024; Revised April 2, 2024; Accepted April 10, 2024.; Published online June 30, 2024.
© Korean Association of Oral and Maxillofacial Surgeons. All rights reserved.

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
 Abstract
Peripheral ameloblastoma (PA) is believed to be the rarest variant of ameloblastoma and only has been described in isolated case reports. PA is usually confined to the soft tissues surrounding the supporting tissues of the teeth. Although it manifests nonaggressive behavior and can be treated with complete removal by local surgical excision, long term follow up is mandatory to prevent future recurrence and possible malignant transformation.
Keywords: Ameloblastoma, Odontogenic tumors, Peripheral ameloblastoma, Extraosseous ameloblastoma
I. Introduction

Peripheral ameloblastoma (PA) is a rare benign odontogenic tumor that constitutes 1% to 5% of all ameloblastomas1. PA is confined to the soft tissues surrounding the supporting tissues of the teeth2; however, PA is an invasive lesion and is recurrent, able to undergo a malignant transformation and even cause metastasis3. Few consecutive case series studies on clinical profile and outcome of PA are available, and this disease was described only in isolated case reports in the literature4.

Clinically, PA appears as a painless, exophytic, sessile growth of the gingiva. The tumors usually have a firm consistency, with a smooth surface and a range of color from pink to dark red. Radiologically, PAs are silent because they rarely invade the bone. Biopsy is usually performed for diagnosis of this disease. The best treatment for ameloblastoma is surgical removal. Despite the non-aggressive course and low recurrence rate, long-term follow-up is necessary.

Herein, we report an unusual case of PA in the maxillary gingiva.

II. Case Report

An 80-year-old Caucasian female was referred by her dental practitioner for 12-month presence of a painless exophytic lesion in the interdental papilla between the first and second upper left molars noted in a routine exploration. The patient had no history of trauma or infection. The patient was a nonsmoker and under treatment for hypertension (beta blocker, Atenolol 50 mg; Laboratorios Cinfa). Periodontal therapy combined with antiseptic therapy with chlorhexidine 0.2% (Bexident Post; Isdin) was performed without remission of the lesion. Intraoral examination showed exophytic lesions with a fibroelastic consistency when palpated at the level of the interdental papilla; a 9 mm×7 mm lesion was found on the buccal side, and a 5 mm×5 mm lesion was on the palatal side. The color of the tissue was the same as that of the adjacent mucosa.(Fig. 1) Bleeding did not occur on probing and the involved teeth were viable. Radiologic examination showed horizontal bone loss likely due to periodontal disease. Significant radiographic changes were not observed between 2018 and 2021.(Fig. 2)

Clinical diagnosis was pyogenic granuloma. As PA typically is confined to the soft tissue surrounding teeth and rarely invades the bone, excisional biopsy is recommended to resect visible tumor lesions, followed by curettage of the bony region to support complete extirpation. An excision biopsy was performed under local anesthesia with proper antiseptic measures for resecting tumor lesions. The two excised lesions (buccal and palatal) were immersed in 10% formalin solution and were submitted to histopathological examination.

The patient was examined 7 days postoperatively, and proper healing was observed.(Fig. 3)

Microscopic examination showed partially ulcerated sections of gingival mucosa, with tumor origination in the basal cell layer of the ridges of the lining epithelium and extensive growth, preserving the epithelial basement membrane (no invasive epithelial infiltration). The peripheral tumor cells exhibited hyperchromatic, columnar nuclei with palisaded arrangement and areas of reverse nuclear polarity. The tumor did not present atypia or abnormal mitoses. In addition, intense chronic inflammation, collagen degeneration, calcium salt deposits in the chorion, and neo angiogenesis without a characteristic pyogenic granuloma-like arrangement were observed, which had not been considered for the diagnosis.(Fig. 4, 5) Based on the clinical, radiographic, and histopathological examinations, PA was diagnosed.

Clinical evidence of recurrence was not observed 24 months after surgery.(Fig. 6)

III. Discussion

When the clinical presentation is not pathognomonic, PA is rarely the initial preoperative diagnosis. Clinically, PAs present as firm, painless, exophytic growths usually ranging in diameter from 1 to 2 centimeters5. The surface of the tumor is generally smooth, but a granular or pebbly surface has been described in several cases1,6.

PAs should be differentiated from peripheral reactive lesions such as epulis, pyogenic granuloma, fibroma, peripheral giant-cell granuloma, peripheral-ossifying fibroma, and basal cell carcinoma1. Although rare, peripheral variants of other odontogenic tumors, such as squamous odontogenic tumor, odontogenic fibroma, calcifying epithelial odontogenic tumor, and calcifying cyst odontogenic tumor, should be included in the differential diagnosis7.

PA has a male predominance with a male to female ratio of 1.9:1 and can occur at all ages but most frequently is diagnosed in middle-aged or older adults1. The mean age at the time of diagnosis varies in the range of 48.6 to 60.4 years4,8-10.

A greater predilection (2:1) for dentate regions, close to interdental papilla, has been reported11. The most common location is the mandible, specifically in the gingival area of the canine/premolar area, affecting both the lingual and vestibular areas, although the lingual area is more common9. The anterior region is the second most frequently affected location in the mandible1,6.

In most cases, PA does not involve bone and is not evident on radiography. However, there may be a small depression of the underlying bone surface associated with the tumor, known as “cupping” or “saucerization”6,9. This superficial erosion or depression of the bone is thought to be due to pressure resorption in contrast to resorption caused by neoplastic invasion1.

Microscopically, PAs are characterized by odontogenic epithelium embedded in a stroma of mature fibrous connective tissue1. In the present case, the histopathological presentation followed the pattern of the traditional PA with palisading peripheral cells. An inflammatory component was also observed subjacent to the epithelium12.

Immunohistochemically, PAs show positive reactivity for cytokeratins AE1/AE3, KL1, 34, and E12, as observed in human enamel13. The cellular proliferation rate of ameloblastoma is generally low. PAs generally manifest benign behavior with an average growth rate lower than those of other ameloblastoma subtypes13. The Ki67 protein is positive in PA cells, with the present case showing a Ki-67 cell proliferation index <2%, which is a good prognostic parameter and an indication of a lower rate of recurrence6.

The recommended treatment is conservative supraperiosteal surgical excision with adequate disease-free margins and thorough microscopic evaluation of the margins for any odontogenic islands that may contribute to recurrence14. Recurrence is rare (16%-19%) and considered a sign of incomplete removal rather than aggressiveness9. In cases of recurrence, the treatment choices are the same as for the primary tumor, surgical removal and anatomopathological study. An annual follow-up is recommended because progression to malignancy and recurrence in the form of severe epithelial dysplasia has been reported15.

In conclusion, PA is an uncommon odontogenic neoplasm. The clinical appearance of this tumor is not pathognomonic, and the diagnosis can only be determined based on histological examination. The biopsy result emphasizes the importance of a histopathological study of surgically removed lesions to establish the correct diagnosis.

Funding

No funding to declare.

Authors’ Contributions

C.V.R., R.M.A.O., and M.I.S.J. participated in performing the clinical treatment, and data collection. R.M.A.O. and J.C.B.B. participated in writing the manuscript. N.Q.L. helped to draft the manuscript. All authors read and approved the final manuscript.

Ethics Approval and Consent to Participate

The Committee for Ethics in research at Universidad Alfonso X el Sabio, Madrid, Spain (No. 2023_03/192) approved this case report, which followed the ethical guidelines established in the Declaration of Helsinki by the World Medical Association.

Consent for Publishing Photographs

Written informed consent was obtained from the patient for publication of this article and accompanying images.

Conflict of Interest

No potential conflict of interest relevant to this article was reported.

Figures
Fig. 1. Intraoral parallelized radiographs taken in 2018 (A) and 2021 (B) respectively.
Fig. 2. Clinical image of the lesion. Gingival swelling between first and second upper-left molars affecting buccal and palatal.
Fig. 3. Clinical image healing sites (buccal and palatal) at 7 days postoperative.
Fig. 4. Histological image of Masson’s trichrome stain lesion. A. Origin: masticatory mucosa with marked ridge hyperplasia. Masson’s trichrome staining, ×120. B. The cells in the peripheral zone adopt a palisade distribution with well-polarized nuclei and present the appearance of a lax reticulum at the central level. Masson’s trichrome staining, ×240.
Fig. 5. Inmunohistochemistry study. Peroxidase antiperoxidase stain (PAP). A. Immunohistochemistry for cytokeratin demonstrates the intense positivity of the epithelial ridges. PAP cytokeratins (CKs) AE1/AE3 staining, ×120. B. The nuclear protein p63, which identifies odontogenic epithelial proliferations among others, is positive in this lesion but is not specific for ameloblastoma. PAP p63 1/800 staining, ×120.
Fig. 6. Clinica image 24-month follow-up.
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