Differential diagnosis of pediatric thymus mass

Approach to the differential diagnosis of thymus mass:

  • On CXR look for thymic wave sign + thymic sail sign to determine whether you are looking at a normal thymus
  • US is a great way to differentiate a prominent thymus with the starry sky appearance of normal thymus from a thymus mass
  • If the thymus appears absent in a newborn, consider DiGeorge syndrome
  • Thymic rebound must be differentiated from recurrent tumor in anterior mediastinal mass patients (leukemia / lymphoma) who have finished their chemotherapy
  • Fat and calcium in a thymus mass usually indicates teratoma, fluid in a thymus mass usually indicates thymic cyst or lymphatic malformation, a solid homogenous thymus mass is usually a thymoma