Fig 23.40 
Intrathoracic Goitre: CT scans. 
These are of a diffrerent Patient to 23.39. The higher scan (a) shows bilateral thyroid enlargement with narrowing and displacement of the trachea. The density of thyroid tissue on unenhanced CT is usually  than that of other soft tissues because of the iodine content of the gland. This is not particularly obvious in this patient. The lower scan (b) shows extension of the right lobe into the posterior mediastinum with patchy enhancement following intravenous contrast.