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.

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)

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 cases^1,6.

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 years^4,8-10.

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 mandible^1,6.

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.