MR imaging of posterior mediastinal thymus.

The diagnosis of posterior mediastinal extension of thymus was made by magnetic resonance imaging, which showed (a) continuity of the normally placed thymus with a posterior mediastinal mass, (b) identical signal characteristics between the anterior and posterior components, (c) homogeneous signal intensity greater than muscle and less than fat on T1- and moderately T2-weighted images which is characteristic of thymic tissue, and (d) characteristic posterior extension of the thymus between the superior vena cava and trachea.