Adenoid cystic carcinoma: a pitfall in aspiration cytology of the thyroid.

While adenoid cystic carcinoma is not an uncommon tumor in the salivary glands, its occurrence in the larynx and trachea is rare. Extension of an adenoid cystic carcinoma of the larynx and trachea to the thyroid with manifestation as a thyroid nodule is extremely rare. However, this possibility always should be considered whenever there are cytologic features suggestive of adenoid cystic carcinoma in thyroid aspirates and when there is a history of adenoid cystic carcinoma in the trachea or larynx or in any part of the body.