Warthin's tumor.

Warthin's tumor, classed as a monomorphic adenoma, ranks second to pleomorphic adenoma in the incidence of benign neoplasms of the parotid gland. By embryologic and clinicopathologic definitions, it is a neoplasm of the parotid gland and its environs, including parotid lymph nodes. Histopathologic diagnosis requires an oncocytic (mitochondria-rich) epithelium and lymphoid stroma. Malignant Warthin's tumors are rare and are carcinomas arising from the ductal component, or non-Hodgkin's lymphomas arising from the lymphoid tissue.