Phantom Nodules Detected by Ultrasound Examination of the Neck: The Possibility of Ectopic Cervical Thymic Tissue in Adults

PURPOSE: The aim of this study was to investigate the ultrasound characteristics and clinical significance of slightly hyperechoic lesions, referred to as phantom nodules, in the perithyroidal area in patients. MATERIALS AND METHODS: A total of 128 patients who underwent thyroidectomy with central neck lymph node dissection at Kuma Hospital in Hyogo, Japan were included in the study. We detected 16 phantom nodules during preoperative ultrasound examinations, defined as slightly hyperechoic masses located in the perithyroidal areas, in 13 of these 128 patients (10.2%; mean age: 55.6 years, range: 36–75 years). RESULTS: All phantom nodules were located in the caudal region of the thyroid gland, and the mean maximum dimension was 7.2 mm. 12 of the 16 nodules were round or oval, while the remaining 4 were fusiform and molded by the surrounding tissue. All nodules were well-defined, solid, homogeneous, hyperechoic masses. No speckled echo pattern, internal linear echo, or vascular flow signal was observed. All 4 nodules subjected to histological examination were composed of ectopic thymic tissue. In 2 of these 4, the parenchyma was severely involuted and almost entirely replaced by adipose tissue. CONCLUSION: To the best of our knowledge, this is the first report wherein some of the detected hyperechoic perithyroidal masses were composed of ectopic thymic tissue, and some were primarily composed of adipose tissue that completely replaced involuted ectopic thymic tissue. The results of the study suggest that these so-called phantom nodules are clinically insignificant and do not require fine needle aspiration cytology or further investigation.