Sialadenoma Papilliferum: An Uncommon Verruco-Papillary Lesion of the Oral Cavity

Abstract

Sialadenoma papilliferum (SP) is a rare benign neoplasm, commonly affecting the minor salivary glands of the palate. Here we report a case SP, clinically presenting as a verruco-papillary lesion, which was diagnosed based on its characteristic histopathologic features, along with a brief review of literature.

Introduction

Sialadenoma papilliferum (SP) is a rare, benign neoplasm, commonly affecting the minor salivary glands of the palate. SP frequently appears as a well-circumscribed, white, exophytic, asymptomatic, slow-growing mass with a papillary surface, often mimicking other verruco-papillary lesions of the oral cavity, making its diagnosis a challenging process [1]. Histologically it bears close resemblance to cutaneous syringadenoma papilliferum of sweat gland origin [2]. The lesion usually arises from the posterior part of the hard palate in middle aged or elderly men. Here, a case of minor salivary gland SP is presented.

Case Report

A 62 years old male patient reported with the complaint of growth on the right side of the palate which increased to the present size over a period of 2 years. Although the growth is not associated with pain, patient complained of local discomfort due to the lesion. On intra-oral examination a pedunculated lesion which measured approximately 1 × 0.5 × 0.5 cm³ was seen 1 cm away from the midpalatal raphae on the right side, just behind the rugae area. The growth was pinkish with whitish areas of keratinization, and showed few papillary verrucous projections over the surface (Fig. 1). The clinical provisional diagnosis was made as squamous papilloma or irritational fibroma. The H&E sections of the excised specimen showed hyperkeratinized, hyperplastic stratified squamous epithelium with exophytic projections supported by fibro-vascular connective tissue core. Beneath the epithelium, glandular component composed of irregular, dilated tortuous convoluted duct/ cyst like spaces with papillary infoldings, lined by a bilayered epithelium of columnar cells resting on cuboidal cells, was noted (Fig. 2a, b). Areas showing ductal epithelium in direct connection with squamous epithelium were also seen in the clefts produced between the epithelial papillary projections (Fig. 2c). Moderate amount of chronic inflammatory cell infiltrate along with epithelial microabscess was also evident. All these characteristic histopathologic features were suggestive of SP without necessitating immunohistochemical analysis.

Fig. 1.

Verruco-papillary lesion on the hard palate in a geriatric male patient

Fig. 2.

a, b Exophytic epithelial projections overlying endophytic convoluted ductal proliferations, lined by bilayered epithelium (H&E, 100X) and c Transition from squamous epithelium to ductal epithelium at epithelial clefts (H&E, 400X)

Discussion

Salivary gland tumors are a relatively rare and morphologically diverse and complex group of neoplasms, considered as one of the most difficult areas of diagnostic pathology. With the introduction of sophisticated techniques, the salivary gland tumors are now classified not just based on the histomorphological similarity (pattern matching), but based on immunohistochemistry and molecular techniques [3]. In the current classification, SP is given its own category and is no longer a “ductal papilloma” [4].

SP is a rare benign neoplasm estimated to account for less than 1% of all minor salivary gland tumors and 3–5% of head and neck tumors [5]. Since the first documentation by Abrams and Finck in 1969, only 64 intraoral SP have been reported till now in the English literature [1], although about 25 cases have been reported in extra-oral sites like nasal cavity, parotid glands, and rarely in the bronchus, trachea and esophagus also [5–6]. SP shares a histopathologic similarity and harbor the same genetic alterations, BRAF V600E or HRAS mutations, with syringocystadenoma papilliferum originating from the sweat glands [7]. SP has a controversial histogenesis. Based on light microscopy, immunohistochemistry, and electron microscopy, variable results have been suggested for SP’s cell of origin, including excretory duct or excretory duct reserve cells, intercalated duct cells or myoepithelial cells, while some other investigators believe it to be a result of focal hyperplastic and metaplastic process after salivary duct obstruction rather than a true neoplasm [1, 5, 8]. Despite the disputed histogenesis, BRAF analysis and SOX10 immunostaining can be useful to make a definite diagnosis [5]. Two distinct molecular sub-types of SP are identified: (1) classic SP, which is strongly positive for SOX10 BRAF V600E mutations; and (2) oncocytic SP, which is SOX10 negative and is BRAF wild-type. However, both the types are analogous morphologically based on their similarities in anatomic distribution (oral cavity), tumor growth pattern (exophytic squamous and inverted glandular components), and immunohistochemistry (CK13 positive squamous elements, CK7 positive glandular elements with p63-positive basal layer) [2].

SP presents as a slow growing neoplasm with limited growth potential with an average size of less than 1 cm at diagnosis [9]. It shows a wide range (2 to 96 years) of age distribution with highest incidence in the sixth to seventh decades, with a higher prevalence among males. Intra-orally, the most affected site is the palate, particularly the hard palate and other sites include the junction of the hard and soft palate, soft palate, buccal mucosa, upper lip, mandibular retromolar area, floor of the mouth, tongue, and left faucial pillar [1, 5]. Clinically, SP often mimics squamous papilloma, but other considerations for provisional diagnosis includes verrucous hyperplasia, exophytic ductal papilloma, fibroma, hemangioma, mucocele, salivary gland neoplasm, warty dyskeratoma, cystadenoma, cystadenocarcinoma or verrucous carcinoma [5, 7, 9]. However, the characteristic histopathologic features of an exophytic proliferation of papillary stratified squamous epithelium and a contiguously endophytic salivary ductal proliferation underneath with stellate to fissure-like lumens and distinct distribution of different cell types in SP, unambiguously distinguishes the lesion from the remaining entities [2, 7].

Conservative surgical excision is the treatment of choice considering its nonaggressive biological behavior with good prognosis. However, there are few odd case reports of possible recurrence and malignant transformation published in the literature, although there is insufficient evidence to support malignant transformation from preexisting SP [1, 7].

Conclusion

In conclusion, although rare, SP should be considered for the differential diagnosis of the exophytic oral lesions, specially occurring on the palate. More studies are required to understand its origin, and biological behavior and malignant transformation.

Author contributions

Conceptualization, S.P.G; Data curation, S.P.G., V.W., N.K.; Formal analysis: S.P.G., V.W., N.K.; Resources, S.P.G., V.W., N.K.; Writing- Original draft, S.P.G.; Writing-review and editing, S.P.G., V.W., N.K. All authors have read and reviewed the submitted manuscript and agree to be accountable for all aspects of the work.

Funding

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