Fine-needle aspiration biopsy of cystic pleomorphic adenoma with adnexa-like differentiation mimicking mucoepidermoid carcinoma: a case report.

Although pleomorphic adenomas (PAs) usually can be diagnosed very accurately with fine-needle aspiration biopsy (FNAB), even this common salivary gland neoplasm can be diagnostically challenging and cause pitfalls in cytodiagnosis. In particular, the presence of either cystic changes or squamous, mucinous, or sebaceous metaplasia can lead to a false positive diagnosis of mucoepidermoid carcinoma (MEC). Here, we present a case of a 70-yr-old man with an asymptomatic left deep lobe parotid mass for which CT-guided FNAB was performed. The FNAB cytology revealed cohesive clusters of squamous epithelial cells, sebaceous cells, oncocytes, macrophages, and rare myoepithelial cells. Characteristic metachromatic fibrillar chondromyxoid stroma, which usually is seen in PAs, was not seen in the aspirate. Although cytodiagnosis of PAs was suggested based on the presence of other cellular components, resection was recommended. The subsequent parotidectomy specimen revealed an encapsulated cystic PA with mixed appendageal differentiation including areas of squamous, mucinous, sebaceous, and oncocytic metaplasia. Chondromyxoid stroma was only focally present. Presence of squamous, mucinous, and/or sebaceous metaplasia, especially in the absence of chondromyxoid stroma, presents the potential for misinterpretation of the FNAB as indicative of malignancy in general and MEC in particular. Copyright 2005 Wiley-Liss, Inc.