Mucoepidermoid carcinoma of the thyroid: a case report.

Primary mucoepidermoid carcinoma (MEC) of thyroid is an uncommon tumour and reports on its' cytology are consequently scanty. A 46-year-old male presented with a thyroid nodule of nine months duration. Fine needle aspiration (FNA) cytology of the nodule showed features of a malignant tumor that was different from the usual types of thyroid carcinoma. Monolayers and syncytial clusters of round and spindle tumour cells with large vesicular nuclei and single macronucleoli were present. A diagnosis of carcinoma was given with the comment that this was unlike any of the usual types of thyroid cancer and that a metastatic malignancy should be ruled out. The cytological picture of MEC may not always be distinctive enough for accurate tumour typing. Nevertheless the cytological features are usually sufficiently different to rule out all of the usual types of thyroid carcinoma. This distinction may be important from the point of view of differing prognosis in MEC of thyroid (as compared to differentiated thyroid cancers) and the need to exclude a metastatic carcinoma, especially from a primary in one of the salivary glands.