Pleomorphic adenoma (PA), the most common salivary gland tumor, accounts for 54 to 65% of all salivary gland neoplasias and 80% of the benign salivary gland tumors. It most frequently affects the parotid gland, followed by the submandibular and the minor salivary glands. Microscopically, mucous, sebaceous, oncocytic and squamous metaplasia, sometimes with the formation of keratin pearls, may be present, but the latter rarely results in the formation of extensive keratin-flled cysts lined by squamous epithelium. Extensive squamous metaplasia can be mistaken for malignancy, including mucoepidermoid carcinoma and squamous cell carcinoma. Here, we present an unusual case of PA with extensive squamous metaplasia and keratin cyst formations in a minor salivary gland, and discuss its microscopic features, including the immunohistochemical characteristics, and differential diagnosis of this uncommon presentation.

A paracoccidioidomicose é uma doença granulomatosa crônica que induz resposta inflamatória e imune específica. A participação do óxido nítrico (NO), produto da enzima óxido nítrico sintase induzível (iNOS), como uma importante molécula fungicida contra o fungo Paracoccidioides brasiliensis tem sido demonstrada. Com o objetivo de melhor caracterizar as lesões orais da paracoccidioidomicose (OP), propusemos estudo imunohistoquímico das células iNOS+ e das células CD45RO+, CD3+, CD8+, CD20+, CD68+ e mastócitos. As amostras foram distribuídas em grupos de acordo com o número de fungos viáveis por mm². Nossos resultados demonstraram leve imunomarcação para iNOS nas células gigantes multinucleadas (MNGC) e na maioria das células mononucleares (MN), e a proporção de células MN/MNGC iNOS+ na OP foi comparável a do grupo Controle (tecido bucal clinicamente saudável). Adicionalmente, nossa análise revelou similaridade no número de células CD4+ entre o Controle e o grupo de OP com elevado número de fungos. Estes achados sugerem que a baixa expressão de iNOS e a diminuição de células CD4+ na OP podem representar possíveis mecanismos que permitiram a multiplicação local do fungo e a manutenção das lesões bucais ativas.

Paracoccidioidomycosis is a chronic granulomatous disease that induces a specific inflammatory and immune response. The participation of nitric oxide (NO), a product of the inducible nitric oxide synthase enzyme (iNOS), as an important fungicidal molecule against Paracoccidioides brasiliensis has been demonstrated. In order to further characterize the Oral Paracoccidioidomycosis (OP), we undertook an immunohistochemical study of iNOS+, CD45RO+, CD3+, CD8+, CD20+, CD68+ cells and mast cells. The samples were distributed in groups according to the number of viable fungi per mm². Our results showed weak immunolabeling for iNOS in the multinucleated giant cells (MNGC) and in most of the mononuclear (MN) cells, and the proportion of iNOS+ MN/MNGC cells in the OP were comparable to Control (clinically healthy oral tissues). Additionally, our analysis revealed a similarity in the number of CD4+ cells between the Control and the OP groups with higher numbers of fungi. These findings suggest that a low expression of iNOS and a decrease in the CD4+ T cells in OP may represent possible mechanisms that permit the local fungal multiplication and maintenance of active oral lesions.