Clinical Utility of Fine Needle Aspiration Cytology for Adenoid Cystic Carcinoma of the Trachea with Thyroid Invasion: A Case Report.

BACKGROUND Adenoid cystic carcinoma of the trachea (ACCT) is a rare cancer; ACCT with thyroid invasion is particularly rare. We first suspected anaplastic thyroid carcinoma (ATC) but diagnosed ACC after performing fine needle aspiration cytology (FNAC). A tracheal origin was confirmed after operation. CASE DESCRIPTION We report the case of a 77-year-old female presenting to our hospital with acute inspiratory dyspnea requiring emergency tracheotomy. Physical examination revealed a right anterior neck swelling with a hard and unmovable mass. Computed tomography (CT) and ultrasonography (US) showed tumor extension to the right thyroid lobe, and between the first and third tracheal rings, which caused severe stenosis of the lumen. Next, we performed FNAC. Clinical findings were highly suspicious for ACCT with thyroid invasion. Thirty-five days after the first visit to our department, the patient underwent total laryngectomy, cervical esophagectomy, and thyroidectomy with bilateral selective neck dissections at another hospital. The tumor was located in the right posterior wall of the trachea, with extension into the right thyroid gland. Pathological examination showed an infiltrative carcinomatous proliferation with tubular and cribriform patterns. The tumor was classified as pT4N1. A definite diagnosis was made after histopathological analyis of the surgical specimen confirmed ACCT. The tumor was found to be positive for FABP7, a putative prognostic marker of ACC, and metastasized to the lungs 3 years after the surgery. CONCLUSIONS ACCT with thyroid invasion is an extremely rare malignant neoplasm. FNAC was useful for differentiating ACCT from other diagnoses and enabled appropriate surgical treatment.