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Benign tumors of salivary glands:

The benign tumors of salivary gland most often appear in fifth to seventh decades and come into attention due to their rapid growth.

    1. Pleomorphic Adenoma:

These are benign tumors of salivary gland tha consist of mixture of ductal (epithelial) and myoepithelial cells showing both epithelial and mesenchymal differentiaition. These tumors are also called mixed tumors because of their diverse histological components and morphological appearance.

Location:

60-75% arise in parotid gland, 5 to 10% in submandibular gland and are relatively rare in minor salivary gland.

Clinical features:

They can occur at any age but third to fifth decade is common. These tumors present as painless, persistent, slow-growing, mobile, discrete masses within parotid, submandibular or buccal cavity.

Gross findings:

Sharply demarcated or encapsulated. Smooth, shiny gray-white cut-surface. Delicate fibrous septa can be seen. Areas of chondroid differentiation and small cysts are also observed grossly.

Microscopic findings:

  capsule is seen but finger-like projections of tumor can be seen extending through capsule. Epithelial component is arranged in trabeculae, tubules, ductules or non-keratinizing  squamous aggregates. The stromal component is also variable and may include mucoid, myxoid, fibroblastic, cartilaginous, osseus and lipogenic elements.

Pathogenesis:

little is known about origin of these neoplasms except that radiation exposure increases the risk.  A high fraction of these cases is associated with chromosomal rearrangements involving PLAG1. Its over-expression leads to up-regulate genes involved in cell growth.

Treatment and recurrence:

Improperly resected tumor often recurs as multicentric nodules. It happens as a result of shelling out the tumor and leaving behind the transcapsular fingerlike projections of tumor in the adjacent salivary gland tissue. The recurrence rate is as high as 25% in comparison to 4% associated with parotidectomy.

    1. Warthin tumor:

It is second most common salivary gland tumor representing 15% of epithelial tumors. It has strong association with smoking increasing the risk to eight times the non-smokers.

Location: 

almost exclusively in parotid gland and peri-parotid lymph node.

Clinical presentation:

These are more common in males, usually in fifth to seventh decade. 10% are multifocal and 10% are bilateral. Palpable round to oval masses usually 2-5 cm in diameter.

Gross examination:

pale gray cut-surface showing narrow, cystic and cleft-like spaces filled with mucinous or serous  secretions. The cyst contents may even resemble dark motor oil.

Microscopic examination:

An oncocytic epithelial component and a prominent lymphoid stroma. The epithelial component have cells arranged  in two layers forming papillary projections in the cystic lumina.  The cells have eosinophilic granular cytoplasm, hence called oncocytic. Lymphoid stroma resembles normal lymph node with germinal centre formation. The lymphoid stroma can give rise to lymphoma or be a site of metastasis of carcinoma or melanoma.

Genetics:

6p re-arrangements. T(11;19)

Recurrence:

it is only 2% after resection.

    1. Basal cell adenoma:

Precursor of basal cell adenoma is intercalated duct hyperplasia.

Location:

about 70% occur in parotid gland. Rest of them occur in submandibular gland and oral cavity.

Age:

Sixth decade or older

Gross appearance:

sharply circumscribed encapsulated masses.

Microscopic appearance:

Capsule is present. Peripheral cell palisading is a characteristic feature. Two patterns are observed. Tubulotrabecular  showing trabecular arrangement of cells with ductlike lumina. Other is membranous pattern that constitutes of nests of cells separated by hyaline stroma.

Immunohistochemistry:

The tumor cells are positive for Carcinoembryonic antigen (CEA), epithelial membrane antigen (EMA )and cytokeratin.

    1. Canalicular adenoma:

Location: Upper lip

Gross appearance:

It may be well-demarcated nodule, single encapsulated lesion or multinodular growth pattern.

Microscopic appearance:

Small cuboidal or columnar cells arranged in tubules or ducts giving a beaded appearance. Stroma is loose and myxoid showing prominent vascularity.

Immunohistochemistry:

cytokeratin and S-100 are positive. Glial fibrillary acidic protein (GFAP) is focal positive

    1. Myoepithelioma:

These are benign salivary gland tumors composed entirely of myoepithelial cells.

Location:

Parotid gland is most common location. Around 50% of such lesions arise in parotid gland. Rest of the tumor arise in minor salivary glands mainly palatal in location.

Clinical presentation:

slow growing masses usually in fourth decade

Gross appearance:

encapsulated or well-demarcated lesions.

Microscopic appearance:

Three types of cell variants are seen. Spindle cell variant composed of spindle cells arranged in storiform, herringbone or fascicular patterns with little or almost no stroma in between. Plasmacytoid or hyaline cell variant consists of cells with eccentrically place nucleus, eosinophilic glassy cytoplasm arranged in nests and groups. Myxoid stroma is present in the background. Third variant is composed of clear cells

Terminology shifts in WHO classification:

    • Sebaceous and non-sebaceous lymphadenomas have been joined under the heading of Lymphadenoma
    • Inverted and ductal papilloma are now considered under the heading of Ductal papilloma
    • Metastasizing pleomorphic adenoma is shifted to subcategory of Benign Pleomorphic adenoma

New benign entities added:

    • Hemangioma
    • Lipoma
    • Nodular fasciitis   

 

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