Michael P. D'Alessandro, M.D.
Peer Review Status: Internally Peer Reviewed
The thymus is normally prominent in the newborn and increases in size during the first few months of life. The appearance of the thymus may resemble a sail ("sail sign"). The thymic margin may have a wavy appearance ("thymic wave") due to indentations caused by the anterior costal impressions on the soft thymus. A prominent thymus implies a healthy infant, while stressful situations (infection, etc.) lead to thymic atrophy. The thymus decreases in size by 1-3 years old. By 4 years of age it can only be seen on a CXR in 2% of patients, but it is usually seen on CT of the chest in patients less than 20 years old. The thymus changes in size and shape during inspiration and expiration with a relative increase in transverse thymic diameter during expiration that returns to normal with inspiration.
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