Salvatore. Incidental detection of a mediastinal mass in a asymptomatic patient poses a not easy diagnostic problem. For solid masses or cysts, histology or cytology is often necessary. Although substernal extension of a cervical goiter is common, totally intrathoracic primary thyroidal mass is unusual. We describe a rare case of heterotopic accessory mediastinal thyroid in a patient completely asymptomatic both for signs of thyroid dysfunction and mechanical compression. Radiological and hormonal 6 and 12 months follow-up is reported
