Ultrasonographic findings of tracheal adenoid cystic carcinoma with thyroid invasion and mimicking thyroid tumors: a case report.

Background: Tracheal adenoid cystic carcinoma (TACC) is a rare, low-grade malignant tumor. The primary TACC usually metastasizes to the lung and bone, rarely involving the thyroid. Although some previous reports have described the imaging features of TACC with thyroid invasion, the multimodal ultrasound findings of TACC with thyroid invasion and mimicking thyroid tumors have not been reported before. Case Description: A 69-year-old woman who had been experiencing hoarseness for 2 years and a thyroid nodule for 2 months was presented to our clinic. Conventional ultrasound showed a hypoechoic nodule about 33×25×50 mm in the left lobe and isthmus of the thyroid, adjacent to the trachea and extending to the right lobe. Contrast-enhanced ultrasound (CEUS) showed that the nodule was unevenly enhanced, with iso-enhancement in the periphery and hypo-enhancement in most of the central area. Shear wave elastography showed that the maximum Young's modulus of nodules was 237.5 kPa, the minimum was 0.1 kPa, and the average was 60.5 kPa. Triiodothyronine, thyroxine, thyroid stimulating hormone and calcitonin were within the normal range. The patient underwent radical surgery with an uneventful postoperative recovery. Combined with the intraoperative findings and pathological examination, the diagnosis of TACC with thyroid invasion was made. Conclusions: This rare case shows that TACC invading the thyroid may be manifested as a thyroid tumor on ultrasound. Preoperative pathological examination and comprehensive imaging examination are of great significance for the clinical management of patients. We also reviewed the literature on the imaging findings and clinical performance for TACC with thyroid invasion.