Pediatric Thymus Rebound

  • Etiology:
    — Thymus shrinks due to stress (pneumonia, steroid therapy, chemotherapy, radiation therapy, surgery, burns)
    — Thymus returns to normal or increased size when patient recovers over several months
    — Thymus is normal microscopically
  • Imaging: Thymus disappears and then reappears but stops growing when it reaches its normal size and has homogenous appearance
  • Imaging US: Normal thymus can be confirmed which shows characteristic starry sky or dot-dash appearance of thymus
  • DDX: Recurrent tumor in a patient with an anterior mediastinal tumor
    — Thymus is soft and is displaced by surrounding structures
    — Anterior mediastinal tumor is hard and displaces surrounding structures
  • Complications:
  • Treatment:
  • Clinical:

Radiology Cases of Thymus Involution and Thymus Rebound

Radiology Cases of Thymus Involution and Thymus Rebound Due to Bacterial Pneumonia

CXR of thymic rebound
CXR AP from one month ago (left) shows evidence of a right lower lobe infiltrate and right pleural effusion due to bacterial pneumonia. The superior mediastinum is narrow. CXR AP taken today (right) shows resolution of the pneumonia and interval reappearance of the thymus.

Radiology Cases of Thymus Involution and Thymus Rebound Due to Viral Pneumonia

CXR of thymus rebound
CXR AP (left) shows central airway thickening and lung hyperexpansion. The thymus is not visible. Repeat CXR AP obtained 3 months after resolution of respiratory symptoms (right) shows normal central airways and lung expansion. The thymus is now well visualized and is normal in appearance.