Neck mass with marked squamous metaplasia: a diagnostic pitfall in aspiration cytology.

Fine-needle aspiration cytology (FNAC) is a highly accurate tool for the diagnosis of pleomorphic adenomas; however, this common salivary gland neoplasm can be diagnostically challenging, causing pitfalls in cytodiagnosis. A 50-year-old woman suffered from a painless, slowly-growing mass in the right posterior upper neck for 5 months. FNAC from this mass revealed many discohesive parakeratotic cells and keratin flakes, and a few stromal elements. Under the impression of metastatic well-differentiated squamous cell carcinoma, the tumor mass was totally excised. Histology confirmed a pleomorphic adenoma with marked squamous metaplasia and frequent keratin pearl formations without the evidence of malignancy. Pleomorphic adenoma occasionally reveals focal squamous metaplastic changes, when extensive, it may be misdiagnosed as metastatic well-differentiated squamous cell carcinoma in FNAC, particularly in the neck region.