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). Tracheal origin was confirmed postoperatively.Case Description: A 77-year-old woman presented to our hospital with acute inspiratory dyspnea requiring emergency tracheotomy. Physical examination revealed swelling of the right anterior neck and a hard, immobile 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. We performed FNAC. Clinical findings were highly suggestive of ACCT with thyroid invasion. She underwent total laryngectomy, cervical esophagectomy, and thyroidectomy with bilateral selective neck dissection at another hospital. The tumor was located in the right posterior wall of the tra-chea and extended into the right thyroid gland. Pathological examination showed infiltrative carcinomatous proliferation with tubular and cribriform patterns. The tumor was classified as pT4N1. A definite diagnosis was made after histopathological analysis of the surgical specimen confirmed ACCT. The tumor was positive for FABP7, a putative prognostic marker of ACC, and metastasized to the lungs 3 years after 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.(J Nippon Med Sch 2022; 89: 460 465)