Normal Thymus | Pediatric Radiology Reference Article | Pediatric Imaging

CXR: gone by ~ 5 years old, findings that help diagnose a normal thymus include 1) thymic wave sign = undulating thymus contour caused by ribs making impression on soft thymus that appear like waves and 2) thymic sail sign = triangle-shaped inferior margin of a normal thymus seen more commonly on the right upper lobe than the left upper lobe
US: use a a problem solving tool, thymus has starry sky appearance
CT: gone by ~ 17 years old
Fluoroscopy: moves with inspiration / expiration – increases in size in expiration
Imaging: shrinks when stressed by infection or malignancy, rebounds when disease resolves / treatment is over, make sure enlarging thymus not due to recurrent tumor in oncology patients
DDX: upper lobe consolidation due to pneumonia or atelectasis
— Pulmonary vascularity can be seen through a normal thymus, pulmonary vascularity cannot be seen through pneumonia or atelectasis
DDX: anterior mediastinal tumor
— Thymus is soft and is displaced by surrounding structures
— Anterior mediastinal tumor is hard and displaces surrounding structures
DDX: lymphadenopathy
— Lymph nodes are hard + cause airway obstruction + airway shift and lymph nodes are more mass like + resemble lobes of thymus less
— Thymus is soft + compresses + displaces nothing, moves with inspiration / expiration – increases in size in expiration