An unusual mediastinal mass

We report a case of a mediastinal mass indenting the left lateral tracheal wall of a 35-year-old male who presented with weight loss, cough and breathlessness. Flow volume loop and thyroid function tests were normal and thyroid peroxidase antibodies were negative. Technetium scintigraphy and positron emission tomography both showed no uptake. Endobronchial ultrasound-guided fine needle aspiration confirmed ectopic mediastinal thyroid tissue. Mediastinal ectopic thyroid tissue is very rare. Most patients are asymptomatic and euthyroid with positive signals on scintigraphy. False negative technetium scintigraphy can occur in areas of necrosis, carcinoma and from substernal tissue. Ectopic thyroid tissue is a rare but important differential diagnosis when investigating mediastinal lesions and should be considered even if scintigraphy is negative in the right clinical context. Endobronchial ultrasound-guided fine needle aspiration can be used when scintigraphy is not diagnostic.