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A 42-year-old woman presented with a gingival mass in the lingual vestibule of the mandibular incisor premolar region. On intraoral examination, the swelling was non-tender and firm. Surgical excision was carried out and subsequent histopathological examination revealed areas resembling ameloblastoma-like and basaloid areas with atypical features suggestive of basal cell carcinoma. Immunohistochemical analysis was carried out to ascertain the origin of the lesion.
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Correspondence to Professor Shivjot Chhina, [email protected]
Background
These lesions rarely occur in the gingiva. Owing to the overlapping histological features with basal cell carcinoma (BCC) and ameloblastic carcinoma, diagnosis is challenging. A proper assessment of the case by conferring with a periodontist and an oral pathologist is warranted, so as delineate a proper treatment plan.
Case presentation
A 42-year-old woman presented with a painless gingival swelling. The lesion presented on the lingual aspect extending from the permanent mandibular right incisor up to the mesial of the right mandibular first molar. The patient reported of difficulty in speech, as the lesion was interfering with her tongue. On intraoral examination, the swelling was non-tender and firm, and measured 2×1.5 cm (approximately) (figure 1). General examination was unremarkable and no associated lymphadenopathy was detected.
Investigations
Haematological and biochemical values were in the normal range. Orthopantomogram and intraoral periapical X-ray did not reveal any bony involvement.
Differential diagnosis
The preoperative differential diagnosis included: gingival tumours, such as peripheral ossifying fibroma, peripheral odontogenic fibroma and inflammatory hyperplastic lesions such as pyogenic granuloma or peripheral giant cell granuloma.1
Peripheral ossifying and odontogenic fibromas show varied clinical appearances that may closely resemble those of peripheral ameloblastoma (PA). Therefore, clinical features of these lesions are not pathognomonic, and histopathological examination is essential for the definitive diagnosis. On the other hand, peripheral fibromas usually lead to a separation between adjacent teeth and radiopaque foci, which can be appreciated radiographically.2
Inflammatory gingival hyperplasias are a second group of conditions that need to be considered in the differential diagnosis. Commonly, these are associated with chronic irritants, such as calculus or overhanging margins of dental restorations, which on elimination usually result in regression. Pyogenic granuloma is an asymptomatic mass that appears red and bleeds readily and presents a rough, ulcerated necrotic surface. Peripheral giant cell granuloma appears red, pink or bluish in colour, is most often nodular or polypoid in shape, and may be soft to hard in consistency.2
PA presents histological characteristics that can be similar to BCC, basaloid variant of squamous cell carcinoma and ameloblastic carcinoma (dedifferentiated),3 as these tumours exhibit similar basal cell proliferation forming epithelial strands. PAs usually arise from the gingival epithelium,45 whereas oral BCCs rarely, if ever, originates from gingival epithelium.67 BCC is a neoplasm occurring on the skin, with a variable morphology and a wide age range of incidence. Therefore, previously reported cases of so-called intraoral BCCs (of the gingiva) may, in retrospect, be considered to be ameloblastic carcinoma of the secondary type (dedifferentiated).8 Ameloblastic carcinoma, however, can be differentiated due to presence of mitotic figures, areas of necrosis and varied degree of anaplasia.
Treatment
Complete surgical excision of the lesion followed by curettage was carried out.
Outcome and follow-up
Microscopic evaluation revealed parakeratinised stratified squamous epithelium with basal cell layer showing proliferation at multiple sites into the underlying connective tissue as strands, nests and islands of tumour cells. Follicular islands showed peripheral palisading, with cells in the centre resembling stellate reticulum. Other areas displayed a basaloid appearance with a few atypical cells (figure 2). Cytokeratin (CK) 19 analyses revealed expression in the basal cells, stellate reticulum cells and a few peripheral cells (figure 3). These features are considered characteristic of PA.
The patient has been on regular, periodic follow-up for more than 2 years and has not presented with any recurrence of the lesion.
Discussion
PA is a painless, sessile, firm and exophytic growth with no radiographic involvement, as also seen in the present case. However, a few of the reported cases have shown radiographically superficial erosion, depression or saucerisation of the involved bone.5 The mandible is a more common site than the maxilla, with the ratio being 2.5:1. In the mandible, the lingual aspect of the premolar region, with 32.6% incidence, is the most common site for PA, as described in our case, followed by the anterior mandibular region, with 20.7% incidence. In the maxilla, the soft palatal tissue of tuberosity accounts for 11.1% of cases. The male to female ratio is 1.9:1 compared with 1.2:1 seen in solid multicystic ameloblastoma (SMA).9 Mean age of occurrence is 52.1 years with mean age of men 52.9 years, slightly higher than that of women, for whom it is 50.6 years; however, in the present case, the age of occurrence was 42 years.
Microscopic examination revealed a tumour consisting of proliferating odontogenic epithelium that exhibited the same histomorphic cell types and patterns seen in SMA. In some cases, a basaloid lesion without classic follicular component is seen, which shows a similarity to BCC.
Two main theories regarding the histogenesis of PA are conjectured. Some tumours are located completely within the gingival connective tissue derived from the dental lamina.51011 On the other hand, many cases of PA present in a very close relationship with the surface epithelium, suggestive of an origin from the surface epithelial layer.12
Immunohistochemical analysis using CK, mainly CK 19, has been carried out to ascertain the odontogenic origin as opposed to origin from the basal cell of gingival epithelium. CK 19 expression is seen in basal cells, suprabasal cells and stellate reticulum-like cells of the tumour,1013 as also discerned in the present case. A study by Hakamawa gave insight into CK 19 expression in poorly differentiated carcinoma of the oral cavity, suggesting that tumour cells retain an immature phenotype of their differentiation.14
The current treatment of choice for these lesions is a conservative subperiosteal surgical excision with adequate disease-free margins. Recurrence rate is 16–19%, which is lower than that of SMA.1516 Most commonly, recurrence is attributed to incomplete removal. Long-term follow-up is necessary, as cases of benign PA have been reported to recur and present as ameloblastic carcinoma.1718
Learning points
Although uncommonly, peripheral ameloblastoma does present in the gingiva and should be considered as a part of the differential diagnosis.
Atypical areas with mitotic activity need to be analysed, as a very thin line differentiates peripheral ameloblastoma from ameloblastic carcinoma.
Follow-up is mandated as a few of the reported cases have recurred as ameloblastic carcinoma.
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