title: Sialadenoma Papilliferum with Inverted Pattern in a Young Patient: A Case Report.
abstract: BACKGROUND
  Sialadenoma papilliferum (SP) is a rare, benign neoplasm of salivary gland origin which manifests as an exophytic papillary excrescence of the mucosa. Indeed, SP is both an exophytic proliferation of papillary stratified squamous epithelium above the mucosal surface and an endophytic salivary ductal proliferation beneath the mucosa. It arises predominantly in minor salivary glands and usually affects patients in the age range of 32-87 years, with reports in young patients being exceedingly rare.
  
  
  METHODS
  We report the case of a previously healthy 20-year-old man diagnosed with a nodular mass in the upper lip buccal mucosa. The tumor was excised and submitted for microscopic examination. Histologic examination revealed a biphasic proliferation of papillary stratified squamous and salivary ductal epithelia, both underneath the mucosal surface.
  
  
  CONCLUSIONS
  In this unique case, as the classical SP, the tumor had a biphasic proliferation of squamous and ductal epithelia. However, unlike the classical SP, both epithelia grew under the mucosal surface. As a result, it did not manifest as an exophytic proliferation, but as a nodule. We excluded squamous papilloma, inverted ductal papilloma, intraductal papilloma and mucoepidermoid carcinoma, the principal entities in the differential diagnosis of SP, and concluded it was an SP with inverted pattern.
authors.affiliation: Department of Pathology, Hospital de Santo António - Centro Hospitalar do Porto, Porto, Portugal.
authors.forename: Francisca Emanuel
authors.initials: FE
authors.lastname: Reis de Sá Silva e Costa
authors.affiliation: Department of Pathology, Hospital de Santo António - Centro Hospitalar do Porto, Porto, Portugal.
authors.forename: José Ramón
authors.initials: JR
authors.lastname: Vizcaíno Vázquez
mesh_terms: D000328:Adult; D001706:Biopsy; D003937:Diagnosis, Differential; D006801:Humans; D008297:Male; D012468:Salivary Gland Neoplasms / Q000473:pathology*; D012470:Salivary Glands, Minor / Q000473:pathology*