Infant who was ill one month ago and now has recovered and presents for followup

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.

The diagnosis was thymic rebound.