Fine needle aspiration diagnosis of ipsilateral synchronous neoplasm - mucoepidermoid carcinoma with warthin tumor in parotid gland.

Warthin tumor (WT) owing to its heterogeneous appearance, biological behavior and multicentricity poses a diagnostic challenge to cytologists worldwide. We report a rare double pathology of mucoepidermoid carcinoma (MEC) with WT which was diagnosed by fine needle aspiration (FNA). Cytological smears revealed sheets of epithelial cells and small clusters of squamous cells in a background of mucoid material along with a few small groups and scattered oncocytic cells and inflammatory cells (mainly lymphocytes). In view of the cytological findings various differentials such as oncocytic lesions, benign lesions of the parotid with extensive lymphoid reaction, necrotizing sialometaplasia, WT with extensive squamous/mucoid metaplasia, metastatic squamous cell carcinoma (SCC) with or without cystic change, oncocytic variant of MEC and a possibility of a synchronous MEC with WT were considered. By means of extensive review of the smears and clinic-pathological meets as discussed below, 2 differential diagnoses were given- MEC with WT versus an oncocytic variant of MEC with "?" lymphoid (tumor response) reaction. Subsequent histopathological examination confirmed the diagnosis of MEC with WT. Recent discovery of t(11; 19) translocation generating a novel fusion gene CRTC1/MAML2 which has been demonstrated in both MEC and WT has helped in providing the missing link in confirming the genetic relatedness and proof of development of a subset of WT with concomitant MEC. The case discusses the FNA findings of a rare collision tumor (MEC with WT), its possible differentials and highlights the importance of noting the background material in a case of double pathology on FNA.