| Abstract|| |
Ameloblastoma is a benign, locally aggressive tumor originating from the odontogenic epithelium. It manifests as a slow growing swelling, causing expansion of the jaw bones. Radiologically, it presents as a unilocular or multilocular radiolucency exhibiting a characteristic soap bubble or honeycomb appearance. Ameloblastoma exhibits several histologic patterns of which basal cell variant is a rare entity. The present case report is that of a maxillary ameloblastoma exhibiting a basaloid differentiation that may put one in the mind of a basaloid squamous cell carcinoma or a basal cell carcinoma. Confirmation of such rare variants should be done not only based on histopathology but with the help of supplemental immunohistochemical analysis. The present case report helps in exposing a rare variant of ameloblastoma and emphasizes the role of advanced diagnostic aids such as immunohistochemistry in establishing the diagnosis.
Keywords: Basal cell ameloblastoma, cytokeratin 19, maxillary ameloblastoma
|How to cite this article:|
Ghattamaneni S, Guttikonda VR, Kumari M G, Kumar D R. Maxillary plexiform ameloblastoma showing basaloid differentiation: Report of a rare case with review of literature. Indian J Dent Res 2015;26:633-6
Ameloblastoma is benign, locally aggressive tumor arising from the odontogenic epithelium. Falkson in 1879 gave the detailed characterization of the tumor while the term "Ameloblastoma" was coined by Churchill in 1933.  The lesion accounts for 1% of all tumors of the head and neck region and approximately 11% of all odontogenic tumors. , Potential sources for the development of ameloblastoma in the oral cavity include (1) enamel organ, (2) cell rests of Malassez and Serres, (3) reduced enamel epithelium, and (4) epithelial lining of an odontogenic cyst.  The most common location of ameloblastoma is the posterior region of the mandible with a mandibular to the maxillary ratio of 5:1.  Ameloblastomas of the maxilla are comparatively rare, and the molar area is the most commonly affected site compared to premolar and anterior regions.
|How to cite this URL:|
Ghattamaneni S, Guttikonda VR, Kumari M G, Kumar D R. Maxillary plexiform ameloblastoma showing basaloid differentiation: Report of a rare case with review of literature. Indian J Dent Res [serial online] 2015 [cited 2019 May 24];26:633-6. Available from: http://www.ijdr.in/text.asp?2015/26/6/633/176930
Basal cell variant of ameloblastoma is infrequent and histologically mimic a basaloid squamous cell carcinoma (BSCC) or a basal cell carcinoma (BCC). The intention of the aforementioned case report is to expose such an exceptional variant that has occurred in an unusual location and to provide a brief review of the literature. To the best of our knowledge, this is the 13 th case to be reported in the literature.
| Case Report|| |
A 30-year-old male patient reported to the outpatient department of our institution with a chief complaint of swelling and loosening of teeth in his upper right back tooth region since 2 months. He gave a history of difficulty in breathing through right nostril associated with a change in phonation. Patient's past medical and dental histories were insignificant.
On extraoral examination, a single right submandibular lymph node measuring about 1 cm × 1.5 cm in size was palpable which was tender and firm in consistency. On an intraoral examination, a solitary, painless, diffuse swelling in the right posterior palatal region extending from the mesial aspect of 17 to the distal aspect of 18 was noticed with an obliteration of the right buccal vestibule and Grade III mobility was noticed in relation to 17 and 18. The mucosa over the swelling was erythematous [Figure 1].
An intraoral periapical radiograph revealed root resorption in relation to 17 and 18 [Figure 2]. Orthopantomogram showed a diffuse unilocular radiolucency in the region of 17 and 18 [Figure 3]. Axial section of computerized tomography of the lesion at the level of maxillary sinus revealed a solid lesion occupying the right maxillary antrum with extension into the posterior wall of sinus involving the pterygoid plates posteriorly [Figure 4].
|Figure 3: Diffuse unilocular radiolucency in maxillary right posterior region with haziness in right maxillary sinus|
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|Figure 4: Computed tomography scan showing lesion in the right maxillary sinus|
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Based on the clinical and radiological appearance, a provisional diagnosis of primary intraosseous carcinoma was made. Differential diagnosis included was ameloblastoma, odontogenic myxoma, and central mucoepidermoid carcinoma. An incisional biopsy was performed and sent for histopathological examination. The histological picture displayed an ameloblastomatous epithelium arranged as interconnecting strands, cords, and sheets in a loose connective tissue background.
The whole lesion was then excised under general anesthesia. On subsequent histopathological examination of deeper sections, the peripheral cells of the amelobastomatous epithelium were appearing cuboidal with hyperchromatic nuclei and lacking a characteristic peripheral palisading arrangement [Figure 5]. Characteristic color gradation was also not apparent toward the center of the odontogenic epithelium for the reason that the center being occupied by basaloid appearing in cells in place of stellate reticulum like cells [Figure 6]. There was also no evidence of cystic degeneration in any of the islands. A diagnosis of plexiform ameloblastoma showing basal cell differentiation was considered based on the cellular architecture.
|Figure 5: Plexiform arrangement of ameloblastic epithelium, (H and E, ×100)|
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|Figure 6: Basaloid arrangement of cells in the center and periphery of the epithelial sheet, (H and E, ×400)|
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An immunohistochemical (IHC) analysis with cytokeratin 19 marker was performed to confirm the diagnosis. IHC revealed diffuse positivity for the tumor cells at the periphery and center of the ameloblastic epithelium [Figure 7].
|Figure 7: Tumor cells diffusely positive of cytokeratin 19 marker, (IHC, ×400)|
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| Discussion|| |
Ameloblastomas occurring in the maxilla are relatively rare, usually asymptomatic, and occasionally tooth movement is the first initial presenting sign.  Nasal obstruction with localized facial enlargement associated with swelling of the gingiva or hard palate of the affected region are the usual presenting signs of maxillary ameloblastomas.  As reported in the present case, the patient presented with the loosening of teeth in relation to 17 and 18 associated with difficulty in breathing and change in phonation.
Ameloblastomas exhibit varying histological patterns of which basal cell ameloblastoma (BCA) is a rare entity, and its incidence was reported to be around 2.02%. 
A literature search was done from 1987 to 2014 on the number of published case reports and reviews on basal cell ameloblastoma, and information that was obtained on demographic variables such as age, sex, site along with histopathological features from 12 reported cases are presented [Table 1].
|Table 1: Demographics and histopathological features of previously reported cases |
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BCA was found to be occurring in a wider age group ranging from 12 to 72 years, with a mean age at the time of diagnosis being made in a 4 th decade with an equal incidence among males and females. Literature review also showed more number of cases occurring in the Indian sub-continent. The present case occurred in a 30-year-old male patient.
The most common presenting symptom in basal cell variant is swelling followed by ulceration of the oral mucosa.  In the present case, the patient presented with a diffuse swelling in the right posterior region of the maxilla with the mucosa over the swelling being erythematous.
In terms of histopathology, BCA is usually composed of multiple follicles, strands, and cords of odontogenic epithelium in minimal connective tissue stroma. Therefore, the general histologic pattern of BCA resembles, to an extent, that of a follicular ameloblastoma. Nevertheless, many authors have stated a predominant net-like pattern in BCA. ,, One case of desmoplastic ameloblastoma featuring a basal cell ameloblastoma was reported by Hirota et al. in 2005.  In the present case, a plexiform ameloblastoma showed a basaloid differentiation.
In BCA peripheral cells of the follicles or strands have cuboidal to low columnar cells that exhibit basaloid appearance with lack of reversal of polarity of the nucleus. There is the absence of characteristic color gradation toward the center of the follicle as the center is occupied by basaloid cells replacing the stellate reticulum like cells. , In this case, all the above features were present.
The similarity in the histopathology of BCA with BCC and BSCC might point toward the aggressiveness of this lesion. Therefore, an IHC analysis using cytokeratin marker 19, amelogenin or enamelin can be done as these will stain for the odontogenic epithelium. In the present case, an IHC analysis was performed using cytokeratin 19 marker that revealed the tumor cells that were diffusely positive for the marker indicating that the cells have retained the basal cell characteristics suggesting a high proliferative activity.
Maxillary ameloblastomas are particularly dangerous partly because the bones are considerably thinner than those of the mandible and present weak barriers to spread. Maxillary ameloblastomas tend to form in the posterior segment and to grow upward to invade the sinonasal passages, pterygomaxillary fossa, orbit, cranium, and brain frequently making them lethal. 
Invasive maxillary ameloblastomas with extension into the orbit, frontal sinus, skull base, middle cranial fossa, and petrous apex resulting in the death of the patient have been reported.  Surgical resection of the tumor remains the mainstay treatment modality.
No recurrence of BCA has been reported in the literature, except that one case of recurrent ameloblastoma was a BCA.  Thirty months follow-up of the lesion showed no evidence of recurrence. However, considering the aggressive nature of the lesion long-term follow-up at regular intervals is recommended.
| Conclusion|| |
The occurrence of maxillary basal cell ameloblastoma is very rare and a plexiform ameloblastoma exhibiting a basaloid pattern is the first of its kind to be reported in the literature. Long-term follow-up of the lesion is necessary owing to its site of occurrence and the nature of the lesion.
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Dr. Sravani Ghattamaneni
Department of Oral Pathology and Microbiology, Mamata Dental College, Khammam, Telangana
Source of Support: None, Conflict of Interest: None
[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7]