Parotid gland, Warthin tumour

Warthin tumour (papillary cystadenoma lymphomatosum) is a benign salivary gland tumour strongly associated with cigarette smoking. It is the second most common benign salivary gland tumour behind pleomorphic adenoma and is almost exclusively found in the parotid gland. It can involve bilateral parotid glands in approximately 10% of cases. Malignant transformation is rare. Surgical resection is curative.
Grossly, the tumour is round to oval, soft, encapsulated with a smooth-lobulated surface. Sectioning reveals tan-brown mucoid contents resembling motor oil.

Microscopically, the tumour is characterized by cystic and papillary growth patterns. It is composed of an oncocytic epithelial layer comprised of a bilayer of granular eosinophilic cells (columnar luminal cells and cuboidal basal cells) overlying a dense lymphoid stroma comprised of mature lymphocytes with lymphoid follicles and germinal centres. Less than 10% of Warthin tumours contain metaplastic changes (squamous or mucous cell) or infarction (following prior manipulation).