Hyperplastic intraparotid lymph nodes with incipient Warthin's tumor presenting as a parotid tumor

Reactive follicular hyperplasia of the intraparotid lymph nodes (IPLs) forming a parotid tumor has rarely been reported, and the pathogenesis of Warthin's tumor has not been determined. A case of hyperplastic IPLs with incipient Warthin's tumors presenting as a parotid tumor is presented. A 68-year-old Japanese patient presented with a tumor of the right parotid gland, and the tumor was resected. Pathologic examination showed seven hyperplastic IPLs (3–15 mm in diameter) with follicular hyperplasia with a capsule, marginal sinuses, and high endothelial venules. Very small foci of Warthin's tumor were recognized in two of the IPLs. Non-tumorous ductules were scattered in four IPLs. Immunohistochemical studies showed that the oncocytes of the small Warthin's tumor and the ductular elements were positive for cytokeratin, but negative for carcinoembryonic antigen, vimentin, α -smooth muscle antigen, and S100 protein. The ki-67 labeling was 3%. CD20-positive B lymphocytes were located in the germinal center and peripheral B zone, and CD3-positive T lymphocytes in the interfollicular T zone. The present case suggests that reactive hyperplastic IPLs may form a parotid tumor, and that Warthin's tumor may develop in hyperplastic IPLs at the inception of its tumorigenesis.