Ectopic Mucoepidermoid Carcinoma: A Pitfall on Fine-Needle Aspiration Biopsy

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Mucoepidermoid carcinomas (MECs) can rarely arise outside normal major and minor salivary gland sites in the head and neck. Ectopic MECs are believed to arise from ectopic salivary gland tissue, which most often occurs in cervical lymph nodes, but can rarely be found in other sites throughout the head and neck. Fine-needle aspiration biopsy of MECs at ectopic sites can be confusing, as the clinical differential diagnosis usually does not initially include a salivary gland tumor. In addition, MEC is one of the most common causes of a false-negative fine-needle aspiration biopsy, particularly for low-grade tumors, which are frequently extensively cystic and may be acellular. Features that would support a diagnosis of ectopic MEC on fine-needle aspiration biopsy include abundant thick extracellular mucin, mucinous epithelium, and epidermoid cells. Awareness that salivary gland tumors can occur at unusual sites is key for the pathologist evaluating the aspirate to arrive at the correct interpretation.

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