Ductal papillomas are a group of relatively rare, benign, papillary salivary gland tumours known as inverted ductalpapilloma, intraductal papilloma, and sialadenoma papilliferum. They represent adenomas with unique papillary features with a common relationship to the excretory salivary duct system, a non aggressive biologic behaviour, and a predilection for the minor salivary glands.They tend to occur in the middle-aged and elderly and rarely in children. The three types of ductal papillomas possess distinct clinical and histologic features allowing differentiation from each other and other adenomas with a papillary pattern.

Inverted ductal papilloma

Definition

Inverted ductal papilloma is a luminal papillary proliferation arising at the junction of a salivary gland duct and the oral mucosal surface epithelium and exhibits an endophytic growth pattern that forms a nodular mass.

ICD-O code 8503/0

Synonym

Epidermoid papillary adenoma

Epidemiology

The true incidence of inverted ductalpapilloma (IDP) is unknown, but it is thought to be relatively rare based on the sparse number of reported cases.Lesions have arisen in adults with an age range of 28-77 years and a male predilection {264}.

Localization

All of the reported sites have been in the minor salivary glands—the most common location is the lower lip followed bythe buccal mucosa/mandibular vestibule. Other reported sites have been the palate and the floor of mouth{264}.

Clinical features

IDP typically presents as a pain less nodular submucosal swelling, often with a dilated pore or punctum surfacing the swelling {1046}. Lesions have bee ndescribed as being present from months to several years.

Macroscopy

Lesions have ranged from 0.5-1.5 cm.They are nodular masses that are oftenpapillary and occasionally cystic.

Histopathology

The neoplasms are unencapsulated.Well demarcated endophytic epithelial masses that are typically continuous with the mucosal epithelium. The mucosal epithelium has a central pore-like opening in the mucosal surface. The peripheral borders of the epithelial mass show abroad, smooth “pushing” interface juxtaposed to the connective tissue stroma.The epithelium proliferates in broad papillary projections that extend into the luminal cavity and are composed predominantly of epidermoid and basal cells that show columnar epithelium on thesurface of the papillae. Acinar aggregatesor individual mucocytes can befound in the columnar epithelial layer and/or in the subjacent epidermoid component.The epithelial cells are cytologically bland with little or no pleomorphism.Mitotic figures are rare.

Differential diagnosis

IDP must be differentiated from mucoepidermoid carcinoma since both have epidermoid and mucous cells. Invertedductal papilloma does not have the multicystic, multinodular, and infiltrative growth pattern of mucoepidermoid carcinoma. Papillary features are rarely found in mucoepidermoid carcinomas.

Prognosis and predictive factors

There have been no reported recurrences following conservative surgical excision based on 12 cases with adequate follow-up time {264}.

Intraductal papilloma

Definition

Intraductal papilloma is a luminal papillary proliferation of duct epithelium that arises from a segment of the inter lobularor excretory duct and causes unicystic dilatation.

ICD-O code 8503/0

Epidemiology

The intraductal papilloma is very rare. Age range is 8-77 years with most cases occurring in the 6th and 7th decade of life {264,1375}. Sex distribution is essentially even.

Localization

The minor salivary glands are more frequently involved than the major glands. Intraductal papillomas are most commonly found in the lips and buccal mucosa. Tumours have been reported in the palate and tongue as well. Of the major glands the parotid is most frequently involved, but cases in the submandibular and sublingual glands have also been cited {264,1008,1749}.

Clinical features

Intraductal papillomas of major andminor salivary glands present as painless,well-defined solitary masses or swellings. Duration can range from weeks to years.

Macroscopy

Grossly, intraductal papillomas are well circumscribed,unicystic nodules that range in size from 0.5-2.0 cm. The lumina contain finely granular, often friable tissue and mucinous material.

Histopathology

The tumour is entirely confined within a circumscribed or encapsulated unicystic cavity. The lumen is partially or completely filled with many branching papillary elements consisting of fibrovascular cores surfaced by columnar to cuboidal cells of one to two layers that originate from a focal point in the wall. Mucocytes, often goblet-like, are interspersed throughout the epithelium lining the papillary elements. These mucous-containing cells can be few to many in number.The epithelium that lines the cyst-likecavity is composed of the same type of epithelium as the papillary fronds. In many instances, the cystic structure has a dense fibrous connective tissue wall surrounding it. Cytologic atypia and mitotic figures are virtually absent {264}.

Differential diagnosis

In contrast to intraductal papillomas,papillary cystadenomas are morphologically multicystic with numerous small to medium-sized cystic spaces. In the papillary cystadenoma the intra luminal growth is often characterized by multiple papillary projections with a variety of epithelial cell types, but usually the papillary growth occupies the lumen to a limited degree.

Prognosis and predictive factors

Excision appears to be curative based on five cases with an adequate follow-up of 2-5 years {1186,1302,1375,1829,2039}.

Sialadenoma papilliferum

Definition

Sialadenoma papilliferum is an exophytic papillary and endophytic proliferation of mucosal surface and salivary duct epithelium.

ICD-O code 8406/0

Epidemiology

Sialadenoma papilliferum is a rare neoplasm{2711}. The age range is 31-87years (mean age 59) with a male to female ratio of 1.5:1 {264}.

Localization

The vast majority of cases have occurred in the minor salivary glands. Major salivary gland involvement is very rare with the parotid gland being the most frequently involved. Over 80% of the neo-plasms occur on the hard and/or soft palate. Buccal mucosa is the second most common site. Other intraoral sites are the upper lip, the retromolar pad, and the faucial pillar {264}.

Clinical features

The sialadenoma papilliferum typicallymanifests as a painless, exophytic papillarygrowth that is often interpreted clinicallyas a squamous papilloma. Durationranges from months to several years.

Macroscopy

Gross findings usually show a well demarcated papillary or verrucoid, sessileto pedunculated surface morphology.Overall, the tumours generally range from 0.5-1.5 cm in size.

Histopathology

The neoplasm consists of a biphasic pattern with a glandular component consisting of collections of cysts and duct-like spaces underlying a papillary or verrucous type proliferation of squamous epithelium. These papillary extensions of squamous epithelium are supported by fibrovascular cores and extend above the level of the adjacent mucosa. At or near the base of the fronds there is a transition from squamous epithelium to columnar ductal epithelium, which lines the proliferating ductal elements. These ductal elements consist of small and ectatic ducts, some of which show cystic enlargement. The ducts and their papillary folds are lined by a double row of cells showing a basal layer composed of cuboidal cells and a luminal lining of low columnar cells. Mucocytes can be interspersed throughout the lining of ductal cells as well as in the squamous component.Columnar oncocytic cells may also be present {2344}. The lack of encapsulation of the ductal structures can at times give the false impression of an invasive growth pattern.

Differential diagnosis

The differential diagnosis typically centres around three lesions: squamous papilloma, inverted ductal papilloma,and mucoepidermoid carcinoma.Squamous papilloma is composed entirely of squamous epithelium and lacks the endophytic growth pattern and glandular differentiation of sialadenoma papilliferum. Inverted ductal papilloma incontrast to the sialadenoma papilliferum,lacks the glandular complexity, and is a well-circumscribed tumour with blunted, pushing non-infiltrative margins. The invasive pattern and variable mixture of epidermoid, intermediate, mucous, and clear cells found in mucoepidermoid carcinoma set it apart from sialadenoma papilliferum.

Prognosis and predictive factors

The recurrence rate for sialadenoma papilliferum is in the 10-15% range based on 20 reported cases with adequate follow-up {264}. Therefore, it is characterized by a higher risk of recurrence than the other types of ductal papillomas of the salivary gland.Complete surgical excision is the treatment of choice.