Warthin’s tumor (WT) is considered a benign primary parotid gland neoplasm, which is composed of a mixture of oncocytic cells, basal cells, and stroma that contains numerous lymphocytes. Usually, the mixture is arranged in papillary and cystic structures.
The tumor involves the parotid gland almost exclusively and sometimes the intraparotid and periparotid lymph nodes. It is the second most common primary salivary gland tumor preceded only by pleomorphic adenoma. It comprises approximately 4% and up to 30% of all epithelial salivary gland tumors. Geographical variations have been reported. The tumor occurs most commonly after the age of 40 years with a mean age around the sixth decade. It is known to be more common in Caucasians and Asians than in African Americans. A strong association between cigarette smoking and Warthin’s tumor is well known, but the exact mechanism is unclear. An additional association was reported with history of radiation and pre-existing autoimmune diseases. With the increasing numbers of female smokers in the recent decades, the previously male predilection is now much weaker. WT is a salivary tumor that can be multicentric and is commonly bilateral. The most common presentation is painless mass or swelling of variable duration. Pain or facial paralysis are rare and occur when associated significant inflammation and fibrosis are present. Radiologically, WT is characteristically well circumscribed, partially cystic, and exhibits strong enhancement.
While aspirating a WT and because of the cystic nature of the lesion, sometimes a dirty, dark brown, thick fluid (it has been commonly described in the literature as machine-oil-like content) can be observed. The aspirate smears characteristically contain numerous lymphocytes admixed with epithelial oncocytic cells and a protein-rich background. The background can be appreciated easily on Diff-Quik stain. The lymphocytes are small and appear mature and more commonly monotonous in nature. The epithelial cells are large and polygonal, and they exhibit an abundant, slightly granular cytoplasm. Usually, they are arranged in two-dimensional sheets (Figure 6.1) rather than three-dimensional groups, and occasionally they form papillae. The granular cytoplasm is more evident on Diff-Quik stain (Figure 6.2) where it is deep blue, and it appears grayish blue on the Papanicolaou stain (Figure 6.3). The nuclei are round to occasionally ovoid and can be located centrally or eccentrically with evenly distributed chromatin (Figure 6.4). Small and occasionally larger nucleoli are present. Cell block stained with hematoxylin and eosin stain will recapitulate the features of cytological smears and the histological correlates (Figure 6.5). The oncocytic cells show their bright eosinophilic and granular cytoplasm, as well as the attached underlying lymphocytic rich stroma. Table 6.1 summarizes the key characteristic cytological features. Attention has to be paid for occasional additional features that sometimes can be observed in WT cases, such as squamous and mucinous metaplasia that will be translated to observing few squamous and mucinous cells. The presence of these occasional cells raises the possibility of mucoepidermoid carcinoma and metastatic squamous cell carcinoma. However, identifying the previously mentioned components and the lack of cytological atypia help to support the diagnosis of WT. The other differential is oncocytoma and acinic cell carcinoma. These two neoplasms will not have the additional two components: lymphocytes and the proteinaceous background In addition, oncocytomas are usually solid and not cystic. Therefore, the presence of cystic tumor areas with oncocytes always supports WT diagnosis. Although rare, the presence/>