Unusual presentation of metastatic adenoid cystic carcinoma: a challenge in aspiration cytology of the thyroid

Introduction. Adenoid cystic carcinoma is a malignant neoplasm most commonly originating in the salivary glands. Its occurrence elsewhere is rare and its metastasis to the thyroid gland has been described only once. Case report. We describe the case of a 66-year-old man who presented for a swelling in the midline neck of six months duration. A solitary palpable nodule was identified in the isthmic region of the thyroid. Fine needle aspiration of the nodule revealed high cellularity, a partial microfollicle-like pattern and the presence of small hyaline globules. The neoplastic population was composed of monomorphic cells with basaloid appearance. Thyroid primitivity was excluded on the basis of the negativity for TTF1 and thyroglobulin. As the patient referred an ulcerative lesion of the inferior lip, fine needle aspiration cytology of the lesion was performed, yielding a diagnosis of adenoid cystic carcinoma. Conclusion. The present case highlights the need to be aware of possible metastatic thyroid localisation of adenoid cystic carcinoma also originating in minor salivary glands of the oral cavity. This is a very rare event, but it should be taken into consideration and clinical and cytological findings must be carefully examined.