Ectopic thyroid tissue (ETT) is a rare condition that predominantly affects women, often during periods of hormonal stimulation. Mediastinal involvement is even more uncommon. We present a case of ETT in a male patient with atypical demographics and a history of renal cell carcinoma, presenting as a large mediastinal mass measuring 6.0 × 4.6 × 4.5 cm. The mass had been slowly enlarging over 14 years without prior tissue diagnosis and was compressing the esophagus. Due to high surgical risk, endoscopic ultrasound (EUS) with fine‐needle biopsy (FNB) was performed, revealing benign thyroid tissue. No further intervention was required. Twelve‐month follow‐up imaging confirmed lesion stability. This case underscores the importance of including mediastinal ETT in the differential diagnosis of thoracic masses and highlights the utility of EUS–FNB as a safe and minimally invasive diagnostic tool for establishing a definitive diagnosis, particularly valuable in elderly or high‐risk patients. It also reinforces the expanding role of gastroenterologists in thoracic diagnostics using EUS.
Dimitrov et al. (Thu,) studied this question.