[Cystic myoepithelioma. A rare differential diagnosis of a cystic lesion of the parotid gland].

By sonography, we found a sharply demarcated tumor with cystic areas in the parotid gland of a 41 year old male, indicating Warthin's tumor. Subtotal parotidectomy was performed. Microscopy showed an encapsulated tumor with myoepithelial cells and, in particular, central pseudocysts. Immunohistochemically, the tumor cells expressed cytokeratin 5/6 and S-100 protein as well as smooth muscle-actin. These features led to the diagnosis of a cystic myoepithelioma. Histopathologically, several different lesions of the salivary glands should be considered in the differential diagnosis of myoepithelioma, especially of this hitherto unique case in the parotid gland. The differential diagnoses are reviewed and discussed. Treatment is by surgical resection. Because of the tendency of myoepitheliomas to recur and to malignant transformation, tumor-free margins are recommended.