Peripheral ameloblastoma of the mandible: A case report

Peripheral ameloblastoma of the mandible: A case report

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ARTICLE IN PRESS Journal of Oral and Maxillofacial Surgery, Medicine, and Pathology xxx (2016) xxx–xxx

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Case Report

Peripheral ameloblastoma of the mandible: A case report Takahiro Kaneko ∗ , Satoshi Nakamura, Ryutarou Kawano, Norio Horie, Tetsuo Shimoyama Department of Oral and Maxillofacial Surgery, Saitama Medical Center, Saitama Medical University, Saitama, Japan

a r t i c l e

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Article history: Received 21 December 2015 Received in revised form 20 January 2016 Accepted 30 January 2016 Available online xxx Keywords: Peripheral ameloblastoma Basal cell carcinoma Immunohistochemical examination Mandible

a b s t r a c t The extra-osseous/peripheral ameloblastoma (PA) is a relatively rare subtype of ameloblastoma, which develops in the soft tissues of the gingiva and oral mucosa. In this article, we describe a PA found in the gingiva of the right mandibular premolar region in a 70-year-old male. On oral examination, a firm, pedunculated mass with a granular surface and partial ulceration was found on the lingual gingiva of the right mandibular first premolar to the first molar. The pathological diagnosis of the incisional biopsy specimen was highly suspected to be PA with difficulty to differentiate from basal cell carcinoma (BCC). As the clinical history and features could not help to rule out the possibility of BCC, en bloc resection with safe margins was performed. Immunohistochemically, the tumor cells showed positivity for CK19 and p63 but Ber-EP4 was negative for tumor cells. The final histopathological diagnosis was peripheral ameloblastoma. © 2016 Asian AOMS, ASOMP, JSOP, JSOMS, JSOM, and JAMI. Published by Elsevier Ltd. All rights reserved.夽

1. Introduction

2. Case report

According to the 2005 World Health Organization classification, benign ameloblastoma is divided into four types: solid/multicystic, extra-osseous/peripheral, desmoplastic, and unicystic [1]. The extra-osseous/peripheral ameloblastoma (PA) develops in the soft tissues of the gingiva and mucosa and shows an innocuous clinical behavior. It comprises about 2–10% of all ameloblastomas. PA exhibits histopathological cell types and patterns similar to those of solid/multicystic type ameloblastoma [1,2]. Most cases of PA arise from the tooth bearing region and differential diagnosis include various inflammatory diseases and benign and malignant tumors. PA and basal cell carcinoma (BCC) have similar histological appearance and growth patterns and it is often hard to differentiate them [3]. In this article, we present a case of PA which was difficult to distinguish from BCC based on clinical features and histological examination of the initial biopsy specimen. Immunohistochemical staining of Ber-EP4 for diagnosis is also discussed.

A 70-year-old male was referred by his dentist to our clinic for evaluation of a painless gingival swelling in the right mandible. He noticed the swelling one year before and the swelling had gradually increased in size. He had a past history of angina pectoris and hypertension and these were well controlled by medication. On oral examination, a firm, pedunculated mass with a granular surface and partial ulceration was found on the lingual gingiva of the right mandibular first premolar to the first molar (Fig. 1). There was no obvious lymphadenopathy or other abnormalities in the head and neck region. Computed tomography (CT) demonstrated a mild depression of the lingual alveolar bone in the right mandibular premolar region (Fig. 2). Magnetic resonance imaging (MRI) showed a heterogeneous high signal intensity mass in T2-weighted images, measuring 15 mm × 10 mm and a low signal intensity mass in T1weighted images (Fig. 3A and B). Peripheral bone invasion was not found. The pathological diagnosis of the incisional biopsy specimen was highly suspected to be PA with difficulty to differentiate from BCC because of the small size of the biopsy specimen. As the clinical history and features could not help to rule out the possibility of BCC, en bloc resection with safe margins was performed. The post-operative course was uneventful and there was no recurrence during the one-year follow-up period. Histopathologically, the resected specimen showed that the tumor had continuity with the surface epithelium. The tumor islands consisted of a central mass of loosely connected stellate reticulum-like cells with acanthomatous areas surrounded by a

夽 AsianAOMS: Asian Association of Oral and Maxillofacial Surgeons; ASOMP: Asian Society of Oral and Maxillofacial Pathology; JSOP: Japanese Society of Oral Pathology; JSOMS: Japanese Society of Oral and Maxillofacial Surgeons; JSOM: Japanese Society of Oral Medicine; JAMI: Japanese Academy of Maxillofacial Implants. ∗ Corresponding author at: Department of Oral and Maxillofacial Surgery, Saitama Medical Center Saitama Medical University, 1981 Kamoda, Kawagoe, Saitama 350-8550, Japan. Tel.: +81 49 228 3687; fax: +81 49 225 1677. E-mail address: t [email protected] (T. Kaneko).

http://dx.doi.org/10.1016/j.ajoms.2016.01.008 2212-5558/© 2016 Asian AOMS, ASOMP, JSOP, JSOMS, JSOM, and JAMI. Published by Elsevier Ltd. All rights reserved.夽

Please cite this article in press as: Kaneko T, et al. Peripheral ameloblastoma of the mandible: A case report. J Oral Maxillofac Surg Med Pathol (2016), http://dx.doi.org/10.1016/j.ajoms.2016.01.008

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Regarding the clinical features, PA is usually painless and the surface is relatively smooth but, in several cases, it has been described as ‘granular’, ‘pebbly’, ‘papillary’ or ‘warty’ in appearance [4] and the irregular surface of PA might lead to a misdiagnosis of malignant disease [5]. In oral BCC, the surface commonly showed non-healing ulceration with or without pain [3]. Ulceration was observed in the present case, probably due to a traumatic bite. In PA, no radiological evidence of bone invasion is usually detected. A superficial erosion of the bone or a superficial bony depression, known as “cupping” or “saucerization” that is thought to be due to pressure resorption may be noticed [4]. BCC may show local bone invasion [6]. Our case also showed a mild depression of lingual alveolar bone in the right premolar region of the mandible.

Fig. 1. Intraoral photograph of a painless firm and pedunculated mass with granular surface on the lingual attached gingiva of the right first premolar to the first molar in the mandible.

layer of columnar cells with well-polarized nuclei (Fig. 4A and B). Immunohistochemically, the tumor cells showed moderate positivity for CK19, strong positivity for p63 but Ber-EP4 was negative for tumor cells (Fig. 5A and B). The final histopathological diagnosis was peripheral ameloblastoma. 3. Discussion Though PA and BCC exhibit similar growth patterns and histological features, they are supposed to be two distinct and separate entities [3,4]. PA is thought to arise from extraosseous rests of dental lamina (rests of Serres) beneath the oral mucosa or from surface epithelium having potential to differentiate into odontogenic epithelium, and BCC is thought to arise from pluripotent basal cells present within the surface epithelium and adnexal structures [1]. BCC is a malignant lesion; therefore, this should be the first consideration in differential diagnosis [3]. In most cases, PA is an exophytic growth localized to the soft tissues overlying the tooth-bearing area of the jaws. The age of the patients ranges from 16 to 92 years with a mean age of 50.2 years. About 50% of the lesions occurred between the ages of 40 and 60. The average size of the lesion measures between 1 and 2 cm. PAs are commonly seen in mandible, especially in the premolar region. The maxilla/mandible ratio was 1:2.4 [2]. In addition, the majority of mandibular PA cases occur in the lingual aspect of gingiva. In the maxilla, however, the most common location was the soft, palatal tissue of the tuberosity area. There was no difference in location between the left and right sides of the jaws [2]. In oral BCC, Woods et al. [3] reported that the mean age of occurrence was 66 years and male to female ratio was 1:2. The most common oral site was buccal mucosa.

Fig. 2. Computed tomography (CT) demonstrating a mild depression of lingual alveolar bone in the right premolar region of mandible (arrow).

Fig. 3. Magnetic resonance imaging (MRI) findings. (A) A heterogeneous high signal intensity mass in T2-weighted images, measuring 15 mm × 10 mm (arrow). (B) A low signal intensity mass in T1-weighted images (arrow).

The histological feature of PA is identical to that of classic intraosseous ameloblastoma. PA exhibited typical odontogenic differentiation mimicking dental lamina or enamel epithelium connected with a basal layer of gingival epithelium [7]. The basal layer cells of the tumor islands of PA are well polarized in a reverse manner and arranged in a palisading fashion [8]. Most of the differential diagnoses can be ruled out by traditional histological examination. But it is often difficult to distinguish between PA and BCC based on histological examination because PA and BCC share similar histological features [3,4]. According to Woods et al., the main histological differences between BCC and PA are as follows: in BCC, the tumor arises from the surface epithelium, mitotic figures and apoptotic cells are scattered, mucoid ground substance is present and the tumor infiltrates widely throughout the connective tissue often exhibiting a prominent retraction artifact [3].

Please cite this article in press as: Kaneko T, et al. Peripheral ameloblastoma of the mandible: A case report. J Oral Maxillofac Surg Med Pathol (2016), http://dx.doi.org/10.1016/j.ajoms.2016.01.008

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Recently, immunohistochemical examination has been suggested to be a useful tool to differentiate between PA and BCC [3,7]. Above all, Ber-EP4, an epithelial cell adhesion molecule which stains the neoplastic basal cells, has been considered to be a consistent and reliable marker in distinguishing between PA and BCC [3]. BCC was positive for Ber-EP4, but PA was negative as in our case [3,8]. Woods et al. described that oral BCC was an extremely rare lesion and that only six cases of oral BCC have been identified by immunohistochemical examination of Ber-EP4 [3]. In addition, epithelial membrane antigen (EMA), a mucin-like glycoprotein, and calretinin, which is considered to be a useful marker for neoplastic ameloblastic epithelium, were positive in PA, but negative in BCC [3,9]. In our case, immunohistochemical staining of CK19 and p63 were also performed and they showed positive staining. CK19, a small (40 kDa) acidic keratin, has been reported to be a marker of odontogenic origin but BCC was also positive for CK19. p63, a transformation-related oncoprotein, has been proposed to be a specific marker of precursor/stem cells in many epithelial tissues and represents a useful marker for assessing the proliferative activity of cells. Both ameloblastoma and BCC showed positive staining of p63 [4]. PA is considered to be less invasive than intraosseous ameloblastoma [1]. The ideal treatment of PA is local excision including a small margin of healthy tissue [4]. BCC is a malignant lesion, and therefore needs wide local excision or resection [3]. The recurrence rate of PA is 16% with an average follow-up of about 3 years [10]. Periodic follow-up is necessary because of the possibility of late recurrence, which has been reported to occur as late as 8 years

Fig. 5. Immunohistochemical stainings. (A) Tumor cells show moderate positivity for CK19 (original magnification ×100). (B) Strong positivity for p63 (original magnification ×100).

after initial surgery [10]. In addition, malignant transformation of PA was reported in several cases. In the present case, as the possibility of BCC could not be ruled out from the clinical features and microscopic findings of the biopsy specimen, en-block resection was performed. In this report, we presented a case of PA which was difficult to differentiate from BCC based on histological examination of the initial biopsy specimen and clinical features. Immunohistochemical examination of Ber-EP4 was useful for the diagnosis of PA. The similarity in histological features and growth patterns of PA and BCC makes it difficult to distinguish between them and may result in confusion. Conflict of interest The authors declare no conflicts of interest. References

Fig. 4. Histopathological findings of hematoxylin–eosin stain. (A) The tumor has continuity with the surface epithelium (original magnification ×40). (B) The tumor islands consist of a central mass of loosely connected stellate reticulum-like cells with acanthomatous areas surrounded by a layer of columnar cells with wellpolarized nuclei (original magnification ×100).

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Please cite this article in press as: Kaneko T, et al. Peripheral ameloblastoma of the mandible: A case report. J Oral Maxillofac Surg Med Pathol (2016), http://dx.doi.org/10.1016/j.ajoms.2016.01.008

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Please cite this article in press as: Kaneko T, et al. Peripheral ameloblastoma of the mandible: A case report. J Oral Maxillofac Surg Med Pathol (2016), http://dx.doi.org/10.1016/j.ajoms.2016.01.008